The Autecology of Eudiaptomus cf drieschi (Poppe & Mrazek 1895 ...
The Autecology of Eudiaptomus cf drieschi (Poppe & Mrazek 1895 ...
The Autecology of Eudiaptomus cf drieschi (Poppe & Mrazek 1895 ...
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<strong>The</strong> <strong>Autecology</strong> <strong>of</strong> <strong>Eudiaptomus</strong> <strong>cf</strong> <strong>drieschi</strong> (<strong>Poppe</strong> & <strong>Mrazek</strong> <strong>1895</strong>)<br />
(Copepoda, Calanoida) in Lake Kinneret, Israel<br />
<strong>The</strong>sis submitted for the degree <strong>of</strong> Doctor <strong>of</strong> Philosophy<br />
Bonnie Rochelle Azoulay.<br />
Submitted to the senate <strong>of</strong><br />
<strong>The</strong> Hebrew University <strong>of</strong> Jerusalem<br />
November, 2001.
This thesis was completed under the supervision <strong>of</strong><br />
Pr<strong>of</strong>essor F. D. Por<br />
Dept. Evolution, Systematics and Ecology,<strong>The</strong> Hebrew University <strong>of</strong> Jerusalem<br />
Pr<strong>of</strong>essor Moshe Gophen<br />
<strong>The</strong> Yigal Allon Kinneret Limnological Laboratory.<br />
Israel Oceanographic & Limnological Research Ltd.
Table <strong>of</strong> Contents<br />
Page<br />
Abstract<br />
Research Objectives 1<br />
1. Introduction 2-8<br />
1.1 Lake Kinneret Background 2-5<br />
Biota 3<br />
1.2 Long-term changes in the Kinneret Ecosystem 5-6<br />
Biological 5<br />
Physical 6<br />
1.3 Previous Diaptomid Data from Lake Kinneret and Israel 6-8<br />
2. Material and Methods 9-19<br />
2.1 Seasonal Abundance 10<br />
2.2 Benthic Resting eggs 10-12<br />
2.3 Diel Survey 12-13<br />
2.4 Experimental studies 14-16<br />
2.4.1 Development 14<br />
Biometrics 14<br />
Stock preparation 15<br />
2.4.2 Data analysis 16-17<br />
2.4.3 Salinity tolerance 18<br />
2.4.4 Food requirements 19<br />
3. Results 20-44<br />
3.1 General Taxonomy 20-22<br />
Description <strong>of</strong> E. <strong>drieschi</strong> from Kinneret 21-24<br />
3.2 Seasonal distribution 24-31<br />
3.3 Sex ratios 32<br />
3.4 Vertical distribution 32-34<br />
3.5 Resting egg distribution 34-36<br />
3.6 Development 38-41<br />
Development Time 39<br />
Development and growth rate 40-42
3.7 Salinity tolerance 43-44<br />
3.8 Food requirements 44<br />
4. Discussion 45-59<br />
4.1 Taxonomical Position 45-46<br />
Biometrics 46<br />
4.2 Ecological implications <strong>of</strong> development 47-49<br />
P/B Ratio 49-50<br />
4.3 Ecological Role <strong>of</strong> resting eggs 50-53<br />
4.4 Vertical distribution 53-55<br />
4.5 Experimental studies 55-59<br />
4.5.1 Salinity 55-56<br />
4.5.2 Temperature 56-58<br />
4.5.3 Food 58-59<br />
5 Conclusions 60-63<br />
6 References 67-77<br />
7 Appendix 78<br />
A 1. Abstract <strong>of</strong> conference presentation<br />
Hebrew Summary
Abstract<br />
Prior to the mid-eighties, diaptomid copepods were only “accidental visitors” in<br />
Lake Kinneret. Early surveys reported sporadic appearances <strong>of</strong> diaptomids in the littoral,<br />
especially after winter floods, but not from other regions. Samples collected after 1986<br />
showed the presence <strong>of</strong> the diaptomid <strong>Eudiaptomus</strong> <strong>drieschi</strong> (<strong>Poppe</strong> & Marzek <strong>1895</strong>)<br />
throughout the pelagic regions <strong>of</strong> the lake. This is the first record <strong>of</strong><br />
E. <strong>drieschi</strong> outside <strong>of</strong> its previous range, as well as the first report <strong>of</strong> a diaptomid species<br />
invading Lake Kinneret. It had been previously recorded from Sri Lanka, Yugoslavia,<br />
Greece, and Turkey. Records <strong>of</strong> the population were begun in 1994. Population densities<br />
and life history parameters <strong>of</strong> this organism have been monitored from a fixed sampling<br />
site, (Station F, 20 m depth) in the northwest region <strong>of</strong> the lake (this study) from 1996.<br />
E. <strong>drieschi</strong> does not appear to produce identifiable cohorts, but reproduces<br />
continuously throughout the time it is present in the water column. In order to obtain<br />
production and biomass estimates, growth and development were measured in the lab.<br />
Individuals were reared at different temperatures and salinity. Duration <strong>of</strong> stage<br />
development and growth increments were measured. Results indicate that temperatures<br />
> 24 0 C are lethal to <strong>Eudiaptomus</strong>, and in chloride concentrations<br />
> 250 ppm, this organism does not develop naturally.<br />
A number <strong>of</strong> noticeable biological and chemical changes have occurred in Lake<br />
Kinneret since 1969. <strong>The</strong> diversity <strong>of</strong> the pelagic zooplankton has increased, with<br />
formerly rare individuals; Chydorus sphaericus (By Birge), Moina rectirostris (Leydig)<br />
appearing more frequently. Also, Conchiloides sp., a colonial rotifer and, Anuraeopsis<br />
fissa (Gosse), a brachionid, are found seasonally in plankton samples. Long – term<br />
records also indicate changes in phytoplankton biomass, particularly the Chlorophyta,
Pyrrhopyta, and Cyanophyta. Salinity, (chloride concentration) decreased from 400 ppm<br />
in the late 1960’s to 208 ppm in the 1980’s. Reduction <strong>of</strong> salinity concentrations is<br />
considered to be the primary driving factor in the establishment <strong>of</strong> E. <strong>drieschi</strong><br />
throughout the lake. Salinity has begun to increase recently and is currently 280 ppm Cl - .<br />
E. <strong>drieschi</strong> shows a strong seasonal periodicity with densities highest in the<br />
winter / spring and very low in summer / fall. Many freshwater diaptomids, produce two<br />
types <strong>of</strong> eggs: a subitaneous or immediately hatching egg and a diapausing or benthic<br />
resting egg. <strong>The</strong> pelagic population <strong>of</strong> E. <strong>drieschi</strong> recovers annually (after overturn)<br />
from a “bank” <strong>of</strong> these benthic resting eggs which were laid down the previous season<br />
when lake temperature increased above their range <strong>of</strong> thermal tolerance (> 22 0 C). <strong>The</strong><br />
benthic resting eggs <strong>of</strong> E. <strong>drieschi</strong> collected from the sediments are not morphologically<br />
different from subitaneous eggs when examined with a scanning electron microscope,<br />
however, they can be distinguished under a light microscope using Lugol’s stain<br />
(Lohner 1990). <strong>The</strong> SEM revealed that the eggs’ surface were smooth, with no spines or<br />
projections. This proposes a potential vector for resting egg transport via the gut<br />
contents <strong>of</strong> fish. Viable resting eggs were found in the gut <strong>of</strong> larval Clarias gariepinus<br />
from the lake. It is possible that E. <strong>drieschi</strong> may have been introduced into the lake by<br />
migrating, piscivorous birds, and distributed by benthic feeding fish.<br />
<strong>The</strong> biological invasion <strong>of</strong> an ecosystem by any organism may be indicative that<br />
the system has undergone modifications, (usually man-made) which allow the invading<br />
species to become established. An invading organism is defined as one that is found<br />
anywhere outside its previous range. A small percentage <strong>of</strong> invasions however, are<br />
actually successful. E. <strong>drieschi</strong> appears to have successfully invaded the Kinneret<br />
system by taking advantage <strong>of</strong> a period <strong>of</strong> low chloride concentration (
occupying a niche and using its adaptive ability to produce resting eggs to escape the<br />
high summer temperatures.
Research Objectives<br />
<strong>The</strong> object <strong>of</strong> this research is to present documentation <strong>of</strong> the life cycle <strong>of</strong> the<br />
diaptomid copepod <strong>Eudiaptomus</strong> <strong>drieschi</strong> (<strong>Poppe</strong> & <strong>Mrazek</strong> <strong>1895</strong>) in Lake Kinneret<br />
during the years 1994-2000, specifically, to follow population dynamics in the field by<br />
measuring secondary production, seasonal distribution patterns, and life stage<br />
development in the laboratory. Preliminary studies were conducted in 1994-95, and<br />
continuous monitoring began in 1996. Ontogenetic distribution, diel changes in the<br />
pelagic population, and benthic resting egg distribution are also investigated. Field<br />
observations in conjunction with laboratory measurements will be used to examine the<br />
temperature and salinity tolerances <strong>of</strong> E. <strong>drieschi</strong>. <strong>The</strong> physical and biological changes<br />
that have occurred in Lake Kinneret which have allowed for the invasion <strong>of</strong> this species<br />
to the pelagic regions <strong>of</strong> the lake will be discussed. A possible vector for resting egg<br />
distribution will be suggested.
1. General Introduction<br />
1.1 Kinneret Background<br />
Lake Kinneret (32 0 42’ and 32 0 53’N) is located in northern Israel in the Syrian-<br />
African Rift Valley. It is a subtropical, monomictic lake, and the only natural freshwater<br />
lake in Israel (Gophen 1984, 1989). Mixing usually begins in early winter (December),<br />
and turnover is usually completed by mid- January, which means the lake is thermally<br />
stratified early summer through late fall (June-December). <strong>The</strong> lake surface area is 170<br />
km 2 with a mean minimum depth <strong>of</strong> 24 m and maximum <strong>of</strong> 42 m when the lake level is<br />
at 209 m below Mean Sea Level. <strong>The</strong> average yearly temperatures range from 14 0 C to<br />
30 0 C. Historically, the lake level has been seen to vary widely from -212 m to -209 m.<br />
Currently, due to consecutive drought years, the lake is at a previously unrecorded low<br />
level <strong>of</strong> –214.23.<br />
<strong>The</strong> lake is situated at the boundary <strong>of</strong> semi-arid and moist climatic conditions. As a<br />
result, there are strong seasonal patterns <strong>of</strong> wind and rainfall in the lake area. <strong>The</strong><br />
amount <strong>of</strong> rainfall throughout the winter period (October-April) is highly variable and<br />
not uniform across the lake. <strong>The</strong> monthly average wind speeds are higher in summer<br />
than in winter, and winter winds are predominantly from the east, while summer winds<br />
are from the west. Two periods <strong>of</strong> “weak wind” generally occur in spring and autumn<br />
(Serruya 1978). <strong>The</strong> external winds in conjunction with the internal temperature regime<br />
greatly influence water movement. A thermal gradient, some 2-3 0 C difference from the<br />
surrounding waters, begins to develop during the spring (March–April) which generates<br />
a changeable barrier (thermocline) in the upper water body (8-10 m). Below this barrier,<br />
oxygen and pH begin to decrease and CO 2 is present on the bottom. Towards the<br />
summer, the increased warming causes the thermocline to deepen which effectively
divides the lake with a warm, oxygenated, CO 2 depleted epilimnion, and a cold, anoxic<br />
hypolimnion with H 2 S and CO 2 .<strong>The</strong> general circulation patterns are seasonal and<br />
determine the formation <strong>of</strong> the thermocline and movement <strong>of</strong> the internal seiche.<br />
<strong>The</strong> main source <strong>of</strong> water to the Kinneret is the Jordan River system. <strong>The</strong>re are also<br />
thermal-mineral springs along the shores and on the lake bottom. <strong>The</strong>se springs<br />
influence the chloride concentration <strong>of</strong> the lake waters. <strong>The</strong> pH values <strong>of</strong> the lake water<br />
are also seasonal, with the lowest values observed during the turnover and highest values<br />
in late spring (7.5-8.9). Oxygen levels in the epilimnion and hypolimnion are influenced<br />
by external weather conditions and consequently vary from year to year.<br />
Bottom sediments are made up <strong>of</strong> a dark, flocculent upper layer <strong>of</strong> 2-5 cm. thickness,<br />
and a more compact, gray material below. Sedimentation rates vary at specific locations:<br />
higher in the north and lowest in the central deep waters. <strong>The</strong>re is also a seasonal<br />
difference in sediment deposition. (Serruya 1978).<br />
Biota<br />
<strong>The</strong>re are over 250 species <strong>of</strong> phytoplankton in the Kinneret including the<br />
din<strong>of</strong>lagellate Peridinium spp. (Gophen & Pollingher 1985). <strong>The</strong> bloom season <strong>of</strong> the<br />
Peridinium occurred with great regularity from late winter to early spring (February-<br />
May) but the highest number <strong>of</strong> species in the lake is represented by the Chlorophytes.<br />
<strong>The</strong> presence <strong>of</strong> such temperate species as Rhodomonas sp. and Cryptomonas sp.,<br />
indicates that cold stenothermic forms can survive during the winter period in warm<br />
lakes. <strong>The</strong> fall season is dominated by nanoplanktonic species with low species<br />
diversity, however during the winter, species diversity is highest. Phytoplankton<br />
biomass peaks in the spring and the diversity begins to decline. Summer shows a drastic<br />
decrease in algal species diversity, with the nanoplanktonic green algae predominating
Over 30 different zooplankton species occur in Lake Kinneret. Zooplankton biomass<br />
is dominated by the Cladocera (58%). <strong>The</strong> most prevalent species are Bosmina<br />
longirostris (O. F. Muller), B. longirostris var. cornuta (Jurine), Ceriodaphnia reticulata<br />
(Jurine), C. rigaudi (Richard), Diaphanosoma lacustris (Korinek), and D. brachyurum<br />
(Lieven). <strong>The</strong> pelagic Copepoda (35%) are represented primarily by the cyclopoids<br />
Mesocyclops ogunnus Onabamiro, 1957 and <strong>The</strong>rmocyclops dybowskii (Lande).<br />
Eucyclops serrulatus (Koch, Sars), a benthic form, appears occasionally in the pelagic<br />
waters. <strong>The</strong>re is a rich benthic harpacticoid fauna (Por 1966, 1968a, 1968b) in the<br />
shallow waters, representatives <strong>of</strong> which appear sporadically among the pelagic<br />
plankton after severe storm events. <strong>The</strong> Rotifera have the lowest biomass (7%), but the<br />
highest number <strong>of</strong> species. <strong>The</strong> predominant forms are Keratella cochlearis (Gosse), K.<br />
valga tropica (Ehrenberg), Synchaeta pectinata Ehrenberg, Asplanchna brightwelli<br />
Gosse, Polyarthra remata Skorikov, and Hexarthra fennica (Levander). Less frequent<br />
members <strong>of</strong> the rotifer plankton are Ascomorpha saltans Bartsch, Trichocerca sp.,<br />
Filinia longiseta (Ehrenberg.) Brachionus angularis (Gosse) and Collotheca sp.. Total<br />
zooplankton biomass is high throughout the winter / spring (42-55 g m -2 ) and ranges<br />
from 25-36 g m -2 during summer/fall. Cyclopoid copepod biomass averages 18 g m -2<br />
and shows little seasonal variation. Cladocera and rotifer biomass is reduced throughout<br />
the summer months.<br />
<strong>The</strong> first report <strong>of</strong> the zooplankton <strong>of</strong> Lake Kinneret was the work <strong>of</strong> Richard<br />
(1890). This work was based on material collected by Barrois who made observations on<br />
the vertical distribution <strong>of</strong> the predominant cyclopoid species in the lake (Serruya 1978).<br />
Zooplankton collected by Annandale in 1912 was analyzed and described by Gurney<br />
(1913). He mentioned the presence <strong>of</strong> Daphnia lumholtzi (Sars) which had not been
found previously. <strong>The</strong> early faunistic survey <strong>of</strong> Bodenheimer (1935) from Lake<br />
Kinneret, listed four cyclopoid species including Cyclops varicans (Sars) which Barrois<br />
had considered as non-resident. Both Gurney and Bodenheimer list species that were not<br />
mentioned by previous surveys: Daphnia lumholtzi and Cyclops leuckarti (Claus) 1857.<br />
<strong>The</strong>se early investigations, however, dealt primarily with samplings from the shallow<br />
littoral (Gitay 1968).<br />
Samples collected from 1948-1950 by Dr. H. Lissner, <strong>of</strong> the Sea Fisheries Research<br />
Station, were examined and reported on in the work published by Komarovsky (1959).<br />
This paper is the first to give a detailed list <strong>of</strong> 22 zooplankton species from the open<br />
water, as well as quantitative data on their seasonality. Yashuv and Alhunis in 1961,<br />
published information from a study conducted in shallow water, during May 1956 to<br />
July 1957, where they listed 35 zooplankton species. In 1968, the newly established<br />
Kinneret Limnological Laboratory began a routine, interdisciplinary monitoring<br />
program <strong>of</strong> the lake. Pelagic zooplankton have been surveyed continuously on a bimonthly<br />
basis, since 1969 to the present, under the supervision <strong>of</strong> Pr<strong>of</strong>. Moshe Gophen.<br />
This investigator has been responsible for the inventory <strong>of</strong> the routine zooplankton<br />
samples from 1980 to the present.<br />
1. 2 Long- term Changes in Kinneret Ecosystem:<br />
Physical<br />
<strong>The</strong> building <strong>of</strong> a dam at the southern end <strong>of</strong> the lake in 1932 at Degania, brought<br />
under man-made control the natural rise and fall <strong>of</strong> the lake level. Operation <strong>of</strong> the dam<br />
caused an overall decrease <strong>of</strong> the average water level, however, the dam ceased active<br />
operation in 1948 and is only used to regulate floodwaters <strong>of</strong> the Southern Jordan River.
<strong>The</strong> National Water Carrier, which was constructed in 1964, is used to pump water from<br />
the lake in order to distribute it to other areas <strong>of</strong> the country, and as a result, also<br />
influences the lake water level. In 1965, a saline spring diversion canal was constructed<br />
to aid in reducing the high concentrations <strong>of</strong> sodium chloride in the lake. Before the<br />
construction <strong>of</strong> the canal, salinity varied from 380-400 ppm Cl - . Since the canal began<br />
operation and in conjunction with heavy flood years, salinity has declined by nearly<br />
30%. <strong>The</strong> annual average for 1988 was 208 ppm Cl - and in the early ‘90’s, it was 218<br />
ppm Cl - . Recently, due to the low lake level caused by severe drought conditions,<br />
diversion <strong>of</strong> spring waters to the canal has ceased and chloride concentration for the lake<br />
is currently (2001) 380 ppm Cl - .<br />
Biological<br />
Changes in the plankton population dynamics reflect some <strong>of</strong> the physical changes<br />
that have recently occurred in the lake. Phytoplankton diversity (non-Pyrrophyta) was<br />
seen to have increased (Berman et al. 1992). Although total zooplankton biomass<br />
declined for a number <strong>of</strong> years (Gophen et al. 1990), zooplankton species diversity <strong>of</strong><br />
the pelagic waters has increased. <strong>The</strong> cladocerans Moina rectirostris (Leydig) 1860 and<br />
Chydorus sphaericus (O. F. Müller) 1785 which had previously been considered<br />
incidental members <strong>of</strong> the benthic fauna (Gophen 1978), are currently routinely found in<br />
pelagic samples. Among the rotifers, Collotheca sp., Anueriopsis fissa (Gosse) and the<br />
colonial Conochiloides coenobasis Hlava, are also regularly found in pelagic samples<br />
(Gophen 1992). <strong>The</strong> copepod <strong>Eudiaptomus</strong> <strong>drieschi</strong> (<strong>Poppe</strong> & <strong>Mrazek</strong> <strong>1895</strong>) is the first<br />
diaptomid copepod to be reported among the “new” members <strong>of</strong> the open water fauna.
1.3 Previous Diaptomid Data from Israel and the Kinneret<br />
Komarovsky’s paper (1959), the first to give a detailed list <strong>of</strong> 22 zooplankton species<br />
including those from the open water, notes especially, “the complete absence <strong>of</strong><br />
Diaptomids among the Copepoda” in the lake, (although they were found in rainpools in<br />
the area). <strong>The</strong> Yashuv & Alhunis paper (1961) listed the diaptomid <strong>Eudiaptomus</strong><br />
gracilis (Sars) among the plankton from a shallow water station in the southwest region<br />
<strong>of</strong> the lake. Por (1968, 1984) recognized E. gracilis as an accidental “visitor”, not<br />
belonging to the Kinneret fauna. Gophen (1972) also recorded the presence (rare) <strong>of</strong> E.<br />
gracilis in the lake and found them represented in the gut contents <strong>of</strong> gray mullet<br />
fingerlings collected from the littoral (Gophen 1979, Shapiro 1998). Dimentman & Por<br />
(1985) collected Arctodiaptomus similis similis (Baird 1859) from the lake during the<br />
winter months, but it was considered to be the incidental result <strong>of</strong> winter floods. Adult<br />
Arctodiaptomus similis similis are occasionally found in inshore waters, in close<br />
proximity to commercial fish pond establishments. Juvenile stages <strong>of</strong> A. similis similis<br />
have never been found in routine samples (pers. obs., author). In 1987, Por (in litteris)<br />
identified the diaptomid copepod that was appearing with increasing frequency in<br />
routine, bimonthly zooplankton samples from pelagic stations in Lake Kinneret as<br />
<strong>Eudiaptomus</strong> <strong>drieschi</strong> (<strong>Poppe</strong> & <strong>Mrazek</strong> <strong>1895</strong>). Pr<strong>of</strong>. Dr. Ertunc Gunduz <strong>of</strong> Hacettepe<br />
University, Turkey, concurred with this identification (pers. comm). It is suspected<br />
(although not validated), that the sporadic reports <strong>of</strong> E. gracilis in the Kinneret may, in<br />
fact, have referred to E. <strong>drieschi</strong>. Specimens <strong>of</strong> E. <strong>drieschi</strong> from the Kinneret are<br />
deposited in the Aquatic Invertebrate Collection at the Hebrew University <strong>of</strong> Jerusalem.<br />
In Israel, the Diaptomidae are represented by four taxa: Lovenula (Neolovenula)<br />
alluaudi (de Guerne & Richard 1890); Arctodiaptomus (Arctodiaptomus) similis similis
(Baird 1859); Arctodiaptomus (Arctodiaptomus) similis irregularis.; and Hemidiaptomus<br />
(Hemidiaptomus) gurneyi canaanita, Dimentman & Por 1985. Lovenula, distributed<br />
throughout Africa and around the Mediterranean, typically inhabits semi-permanent<br />
water bodies and spring basins with chloride concentrations <strong>of</strong> 788 mg l -1 . A. similis<br />
similis is the most common diaptomid in Israel. It is found in temporary rainpools<br />
where salinity is typically low. Hemidiaptomus also inhabits rainpools in the northern<br />
and Coastal Plain areas.<br />
In <strong>1895</strong>, <strong>Poppe</strong> and <strong>Mrazek</strong> found Diaptomus <strong>drieschi</strong> among the material collected<br />
by H. Driesch for the Hamburg Zoological Museum in Sri Lanka (Ceylon). Almost no<br />
work had been done on this species until its revision by Kiefer, in 1932. Kiefer placed<br />
D. <strong>drieschi</strong> in the new genus <strong>Eudiaptomus</strong> because <strong>of</strong> substantial differences in the male<br />
and female 5th legs. E. <strong>drieschi</strong> has been recorded later from southern Yugoslavia<br />
(Lake Skadar, Montenegro), northern Greece (Corfu), and Turkey (Lakes Beysihir,<br />
Egridir, and Kovada), (Kiefer 1968, Gunduz 1998). <strong>The</strong>se water bodies are all<br />
characterized by low salinity, and moderate temperatures.
Fig 1<br />
Map <strong>of</strong> Lake Kinneret -Israel<br />
Kinneret Limnological<br />
Laboratory<br />
F<br />
-220<br />
-230<br />
32<br />
o<br />
50<br />
/<br />
-240<br />
-250<br />
N<br />
o<br />
32 45<br />
/<br />
35 o /<br />
32<br />
5 Km<br />
35 o 35<br />
/<br />
35<br />
o<br />
38<br />
/<br />
Figure 2: Map <strong>of</strong> Lake Kinneret (Seruuya, 1978) showing sampling station F.
2. Methods and Materials<br />
2.1 Seasonal Abundance Studies (Routine Field Sampling)<br />
Samples were collected weekly from Station F (fig 1) using a 20 L plexiglass<br />
Schindler - Patalas trap. Duplicate water samples from 1, 5, 10, and 20 meters were<br />
concentrated through a 20 m mesh sieve net and preserved separately, in 4% sugar<br />
(Haney & Hall 1972) formalin (32g sugar / liter formalin).<br />
<strong>The</strong> entire sample was counted at 20x on a Wildco plankton wheel (10 ml vol.)<br />
with a Wild binocular dissecting microscope All life stages were identified (NI - VI, CI -<br />
V, adult males and females) and counted separately. Egg bearing females were noted<br />
separately from adult females without eggs, and the numbers <strong>of</strong> eggs per female were<br />
counted. Samples from fixed depths were counted separately to examine vertical<br />
distribution, then the counts were pooled for population dynamics.<br />
Diapausing (resting) eggs were distinguished from subitaneous (immediately<br />
hatching) eggs (for one season) in preserved samples by adding Lugol’s solution to the<br />
samples and examining them under an inverted microscope (Lohner 1990).<br />
Sex ratios were compiled using a chi – square test for goodness <strong>of</strong> fit:<br />
X 2 = (f – f^) 2 (1)<br />
f^<br />
f is the observed frequency, and f^ the expected (Sokal & Rohlf 1973).<br />
2.2 Benthic Resting Eggs<br />
Lake bottom sediments were collected monthly using a standard gravity corer<br />
with plexiglas cores (inner diameter: 5.2 mm, length: 47.0 cm.) from the RV Hermona<br />
at sampling station F (maximum depth 22 meters). Cores were also taken from random<br />
sites around the lake. <strong>The</strong> cores were removed to the lab and sediments were processed<br />
within one hour <strong>of</strong> collection, or held upright in cold (4 0 C) storage until sliced. <strong>The</strong><br />
entire core (38.5 cm.) was sectioned into 1 cm. slices. (Investigations showed that viable<br />
resting eggs were rarely found at depths below 12 cm. in the sediments. For that reason,<br />
subsequent cores were sectioned only to 15 cm. depth.) Sediments were weighed and<br />
divided; half for dry weight determination and half for egg counts. Sediment samples for<br />
establishing dry weight were put into pre-weighed foil containers and placed in a drying<br />
oven (100 o C) for 48 hours. <strong>The</strong> sediment portions containing the eggs were processed
using a modification <strong>of</strong> the sugar flotation method introduced by Onbe (1978) and<br />
described in Ban & Minoda (1992). Sediments were washed with filtered lake water<br />
(0.45 µm) through a 45.0 µm mesh sieve. Material remaining on the sieve was rinsed<br />
into 250 ml. Nalgene centrifuge bottles, combined with a supersaturated sugar solution<br />
(1 kg per 1 liter), and centrifuged at 3,000 rpm for 5 minutes. <strong>The</strong> supernatant was then<br />
washed through a 20 µm mesh net to remove the sugar and collect the eggs. Eggs were<br />
carefully rinsed into petri-dishes and counted under a Wild binocular dissecting<br />
microscope. Diaptomid eggs were incubated in controlled light and temperature<br />
conditions (Shel-Lab Low Temperature Incubators) in filtered (0.45µm) lake water and<br />
hatching <strong>of</strong> new - born nauplii was recorded.<br />
<strong>The</strong> number <strong>of</strong> benthic resting eggs per gram <strong>of</strong> dry weight sediment was obtained by:<br />
(a / b) * (# eggs / DW (g) ) = # eggs / g (DW) (2)<br />
where a is the wet weight (g) <strong>of</strong> the sediment portion to be dried, b is the wet weight (g)<br />
<strong>of</strong> the sediment portion for egg counts. <strong>The</strong> number <strong>of</strong> eggs per portion is then divided<br />
by the dry weight (DW) <strong>of</strong> sediments. <strong>The</strong>n the density (number <strong>of</strong> eggs per square<br />
meter) was calculated for each sample by finding the number <strong>of</strong> eggs in the surface area<br />
<strong>of</strong> the core ( S.A. = square <strong>of</strong> r * ), which is divided into the number <strong>of</strong> eggs multiplied<br />
by 10 3 .<br />
.2. 3 Diel Survey<br />
Diel sampling took place at Station F on April 1-2 (spring), September 29-30<br />
(fall) 1997, and June 9-10 (summer) 1998. <strong>The</strong> research vessel (RV Hermona) was on<br />
station throughout the survey periods. Duplicate zooplankton samples were taken every<br />
2 hours with a 20 L Schindler - Patalas trap over a 24 hour period (dawn / dusk / dawn).<br />
Zooplankton samples were taken from depths 1, 3, 5, 7, 10, 15, and 1meter from bottom.<br />
Samples were filtered through a 20µm mesh net and preserved in 4% buffered formalin.<br />
Samples were concentrated through a 20µm mesh net to a smaller volume in the lab.<br />
<strong>The</strong> entire sample was counted and all life stages were enumerated with a Wild<br />
binocular, dissecting microscope. <strong>The</strong> parameters: chlorophyll, oxygen, temperature,<br />
light, and Secchi disc depth were measured.<br />
Phytoplankton chlorophyll a samples were taken with a 5-liter Van Dorn bottle<br />
at each sampling depth. <strong>The</strong> water was filtered on-board for size fractionation <strong>of</strong> net
(>20 µm) and nano (20<br />
m) and nano (
2.4. Experimental Studies<br />
2.4.1. Development<br />
E. <strong>drieschi</strong> was collected from the lake (in the vicinity <strong>of</strong> Station F)<br />
by 5 minute, horizontal plankton net (500 m mesh) tows from the RV Hermona .<br />
Mature adults were individually selected using a modified Pasteur pipette attached to<br />
flexible tubing and controlled by mouth. Animals were maintained in 1liter vessels with<br />
filtered lake water (0.45 m) under controlled laboratory conditions. Prior to each<br />
experiment, animals were incubated for at least one generation at treatment conditions<br />
(temperature and light) and given food ad libitum. Food was a mixture<br />
<strong>of</strong> the algae Chlamydomonas sp. and Rhodomonas sp. (0.6ml in a 1 : 1 ratio) obtained<br />
from stock cultures maintained at the Kinneret Limnological Laboratory.<br />
Length measurements<br />
Body length measurements <strong>of</strong> E. <strong>drieschi</strong> were obtained by using a computer<br />
assisted video camera system, CAPAS (Computer Assisted Plankton Assessment<br />
System, (Hambright 1996) with an inverted microscope. <strong>The</strong> system was calibrated with<br />
a Wild stage micrometer for 500 m (+ 0.15). Copepods were pipetted into 5 ml.<br />
phytoplankton settling chambers (Hydro-Bios, Kiel), and copepod lengths were<br />
measured from the top <strong>of</strong> the head to the end <strong>of</strong> the anal somite (excluding the caudal<br />
ramus). <strong>The</strong> setae were excluded in the naplii length measurements. Although the sex<br />
can be distinguished at developmental stage CIV, males and females were only counted<br />
as such after they had completed the CV molt. At least 50 individuals <strong>of</strong> each life stage<br />
were measured.
Stock preparations<br />
Females with ripe ovaries for the growth and development studies were isolated<br />
and pipetted into 100 ml. Erlenmeyer flasks containing 50 mls. filtered (0.45 m) lake<br />
water. <strong>The</strong> total alga cell concentration <strong>of</strong> the feeding suspension was kept in excess <strong>of</strong><br />
5 x 10 4 cells ml -1 . Algal cell concentration was maintained by determining the<br />
concentration <strong>of</strong> the stock culture by direct cell counts with a hemocytometer ( 0.100mm<br />
x 0.0025 mm 2 ) and adding the appropriate volume to maintain experimental<br />
concentrations. <strong>The</strong> average concentration <strong>of</strong> Chlorophyta in the lake throughout the<br />
period that E. <strong>drieschi</strong> is present, ranges from 1.31 x 10 4 – 9.76 x 10 3 cells ml -1 .<br />
<strong>The</strong>refore it is assumed that experimental conditions provided sufficient nutrition, and<br />
food was not a limiting factor in these experiments<br />
Culture vessels were maintained in temperature controlled (+ 0.1) incubators<br />
(Shel – Lab) in a constant dim light regime. <strong>The</strong> water and food suspension was changed<br />
twice a week. Observations were made at least twice daily for the duration <strong>of</strong> the<br />
experiments.<br />
Mature males, for the development studies, were paired with gravid females, and<br />
pairs were observed regularly until the females produced a clutch <strong>of</strong> eggs. Time elapsed<br />
from successful mating to hatching <strong>of</strong> the eggs was recorded for all pairs. Ten newly<br />
hatched (pre-molt) nauplii from each clutch were removed to new flasks and<br />
development followed and documented to adulthood. Egg development, duration <strong>of</strong> each<br />
naupliar stage, and time spent in each copepodite stage was examined at a range <strong>of</strong><br />
temperatures: 12 0 , 18 0 , 20 0 , 22 0 , and 24 0 C. This range include those temperatures E.<br />
<strong>drieschi</strong> would normally experience in the lake throughout January - June. Animals
incubated at 24 0 C exhibited extremely high mortality, and did not reach the third<br />
naupliar stage. <strong>The</strong>se results were not included in the analysis.<br />
2.4.2 Data Analysis<br />
Secondary production (P) <strong>of</strong> the lake population was calculated based on experimental<br />
measurements utilizing the growth increment method from Downing and Rigler (1984):<br />
P = N (m max - m min ) / D (3)<br />
In this calculation, N, is the average number <strong>of</strong> individuals in a size class at a specific<br />
time. Maximum and minimum biomass (m min and m max ) was measured from the<br />
experiments. Development time (D), was taken as the time it took an individual to grow<br />
from m min to m max .<br />
Finite birth rate (B) was obtained by measuring embryonic development (D) over a<br />
series <strong>of</strong> temperatures in the laboratory, which was then related to the number <strong>of</strong> eggs<br />
from the field data (recruitment <strong>of</strong> eggs to nauplii):<br />
Eggs / L / day = Eggs / Liter / day (4)<br />
D<br />
This is then divided by the size <strong>of</strong> the population at the specific time to give the birth<br />
rate relative to the field population sampled at the time:<br />
B = Eggs / L / day<br />
No./L<br />
(4a)<br />
<strong>The</strong> instantaneous birth rate (b), was calculated as:<br />
b = ln (1+B) (5)
when the population meets conditions where b and d are both constant from t 1 to t 2 as<br />
estimated by the rate <strong>of</strong> change <strong>of</strong> the population:<br />
r =, lnN t – lnN 0 (6)<br />
t<br />
where N 0 is the initial population and N t is the number <strong>of</strong> individuals at a specific time<br />
sampled and t is the time interval.<br />
Instantaneous death rate (d) is then calculated:<br />
d = b – r (7)<br />
Specific length growth rates (C L )were calculated using:<br />
C L = ln (L 2 –L 1 )<br />
t 2 – t 1 (8)<br />
In which L and t are measured initial and final lengths (geometric mean) and<br />
development times found in Tables 1 and 2, respectively.<br />
Biomass was calculated by using the number <strong>of</strong> individuals (N) and their average<br />
weight (M, mg ww ): B = N * M.<br />
Production to biomass ratios (P/B) were calculated for the field population.<br />
Length was measured and weight (biovolume) calculated:<br />
Prolapsed sphere = 4 / 3 (a / 2) * (b / 2) 2 (9)<br />
Where a is measured length in mm and b is width (Bird & T-Praire 1985, Culver et al<br />
1985, Lawrence et al 1987).
2.4.5 Salinity tolerance<br />
Salinity tolerances were measured using varying concentrations <strong>of</strong> an artificial saline<br />
solution for Kinneret water, “Salina” (A. Nishri, pers comm):<br />
NaCl<br />
KCl<br />
MgCl 2 6H 2 0<br />
CaCl 2<br />
Na 2 S0 4<br />
8700 mg / l FLW<br />
350 mg / l FLW<br />
7000 mg / l FLW<br />
147 mg / l FLW<br />
77 mg /l FLW<br />
Table 4: Artificial saline solution (“Salina”) used in salinity tolerance experiments.<br />
<strong>The</strong> following concentrations were used in the experiments: High - 400 mg Cl - / l,<br />
Medium - 280 mg Cl - / l, Lake - 225 mg Cl - /l, and Low - 100 mg Cl - / l. Experimental<br />
concentrations were obtained using “Salina” with filtered Lake Kinneret water (FLW<br />
0.2µm). <strong>The</strong> low concentrations were obtained by diluting filtered lake water (FLW)<br />
with filtered water from the upper Jordan River (20 mg Cl - / l).<br />
Adult animals (5 females, 2 males) were each placed in 32, 50 ml Erlenmeyer flasks<br />
with 25 ml experimental solution. Half <strong>of</strong> the flasks were placed in a temperature / light<br />
controlled incubator at 18 0 C, with dim light conditions and the remaining half were at<br />
12 0 C. Flasks were examined regularly until over 50% mortality was reached.
2.4.4. Food Requirements<br />
Mature adult females (30) were placed in individual cell chambers (Corning cell<br />
wells, 3 mls.), and given high (10 5 cells / ml) and low (7 x 10 3 cells / ml) concentrations<br />
<strong>of</strong> algal food (Chlamydomonas sp.). Concentration <strong>of</strong> algal cells were determined by<br />
direct count <strong>of</strong> observed changes in number <strong>of</strong> cells in suspension, with a<br />
hemocytometer. Percentage survival <strong>of</strong> individuals at the different levels <strong>of</strong> food<br />
concentrations were compared.
3. Results<br />
3.1 Descriptive taxonomy (General)<br />
<strong>The</strong> diaptomid copepods are members <strong>of</strong> the most common group <strong>of</strong> freshwater, filter<br />
feeding calanoids, the Diaptomidae. <strong>The</strong>re are over 400 species in about 50 genera.<br />
<strong>The</strong>y play an important role in freshwater ecosystems as food for fish and invertebrate<br />
predators. As is typical in crustacean morphology, the diaptomid metasome (prosome)<br />
or cephalothorax is divided into a head and thorax, and the urosome is made up <strong>of</strong> the<br />
abdominal and genital segments. <strong>The</strong> urosome terminates with a pair <strong>of</strong> structures called<br />
caudal rami, which end in caudal setae (Williamson 1991). <strong>The</strong> metasome may have<br />
between 4 to 6 segments depending on the species. <strong>The</strong> head bears the first antenna or<br />
antennules, second antenna, mandibles, maxillules, and maxillae. <strong>The</strong> thorax has the<br />
maxillipeds, four pairs <strong>of</strong> swimming legs and a pair <strong>of</strong> modified 5 th legs. Diaptomids are<br />
sexually dimorphic. <strong>The</strong> female 5 th legs are symmetrical and well developed (Fig. 2a),<br />
while the male 5 th legs are highly asymmetrical and modified for reproduction (Fig. 2b).<br />
<strong>The</strong> setation and armature <strong>of</strong> the male right anntenule is also <strong>of</strong> key significance in<br />
species identification (Fig 2c-d). <strong>The</strong> first antennae posses both chemoreceptors and<br />
mechanoreceptors that function in feeding, locomotion, and reproduction. <strong>The</strong>y are not<br />
flexible and are raised or relaxed by increased or decreased blood pressure.<br />
<strong>The</strong> shape and armature <strong>of</strong> the female genital and last thoracic segment are<br />
important morphological features for distinguishing between species (Fig 2e). <strong>The</strong><br />
female genital segment is composed <strong>of</strong> 3 fused segments. <strong>The</strong> antennules <strong>of</strong> the male<br />
diaptomids are asymmetrical, the right antennula is geniculate for grasping the female<br />
during copulation (Fig 3b). It is made up <strong>of</strong> 21-22 segments that can be divided into<br />
three sections.
c)<br />
b)<br />
a)<br />
d)<br />
e)<br />
• Figure 2: a) female 5th leg (P5), b) male 5th leg, c) Detail <strong>of</strong> penultimate segment <strong>of</strong> male right antenna,<br />
• d) detail <strong>of</strong> setation <strong>of</strong> male right antenna, e) Female genital segment showing armature. (Drawings courtesy<br />
<strong>of</strong> F.D. Por).
a.)<br />
b.)<br />
c.)<br />
d.)<br />
• Figure 2a-d.: a)Male fifth leg (P5).,b).Adult male.,<br />
• c). Adult female with egg clutch., d). Adult female with<br />
attached spermatophore.
23<br />
<strong>The</strong> female antennules are symmetrical. <strong>The</strong>y are thin and usually as long or longer than<br />
the length <strong>of</strong> the body. <strong>The</strong>y consist <strong>of</strong> 25 segments (Fig. 3c).<br />
Diaptomids pass through six naupliar (NI-VI) and six copepodid (CI-V) stages by<br />
molting, the final molt produces the adult which does not molt further. Adult females are<br />
fertilized by a spermatophore, which is attached by the male to the female genital<br />
segment (Fig 3d). Females require a new mating for each clutch produced. Eggs are<br />
carried in a single sac under the genital segment.<br />
Developmental Stages<br />
Average body length (in mm) <strong>of</strong> naupliar stages (excluding setae) and average body<br />
length <strong>of</strong> copepodite stages <strong>of</strong> <strong>Eudiaptomus</strong> <strong>drieschi</strong> from Lake Kinneret (excluding<br />
setae) are given in Table 1. Average <strong>of</strong> 50 individuals from each stage.<br />
Table 1: Average body length (in mm.) <strong>of</strong> naupliar and copepodite stages <strong>of</strong> <strong>Eudiaptomus</strong> <strong>drieschi</strong><br />
(average <strong>of</strong> 50 individuals <strong>of</strong> each stage) with standard deviations.<br />
(in mm) NI NII NIII NIV NV NVI CI CII CIII CIV CV<br />
Average 0.141 0.180 0.213 0.252 0.358 0.393 0.499 0.655 0.798 1.107 1.165<br />
St.Dev. 0.002 0.010 0.013 0.01 0.019 0.013 0.019 0.014 0.030 0.105 0.097<br />
<strong>The</strong> NI stage is characterized by 3 pairs <strong>of</strong> incompletely developed appendages (first<br />
antennae, second antennae, mandibles) and no caudal setae. <strong>The</strong> first maxillae appears in<br />
NII. In the later or metanaupliar stages, maxillule develop (NIII, NIV). In the fifth stage<br />
(NV), the maxilla become visible. <strong>The</strong> maxilliped and rudimentary legs are present in<br />
the sixth and final naupliar stage. <strong>The</strong> second pair <strong>of</strong> legs appears in NVI as<br />
unsegmented buds.<br />
<strong>The</strong> copepodite stages are recognized by the number and segmentation <strong>of</strong> legs: 2-5.<br />
In C I, legs 1 and 2 are recognizably developed, but the endopod and exopod are<br />
unsegmented. Leg 3 appears as a “bud”, and after the CII molt, the “bud” becomes a
segmented leg and the next leg bud appears. It is possible to distinguish between the<br />
sexes by stage C IV as all five legs are present, but not fully developed. Development is<br />
completed by stage C V.<br />
<strong>Eudiaptomus</strong> <strong>drieschi</strong> densities in Lake Kinneret,<br />
Station A<br />
Number <strong>of</strong> organisms L -1<br />
20<br />
10<br />
0<br />
1970<br />
3.2 Seasonal Distribution<br />
Figure 6: Multi annual population density <strong>of</strong> E. <strong>drieschi</strong> in<br />
the Kinneret<br />
Densities (number per liter) <strong>of</strong> E. <strong>drieschi</strong> from the KLL database (Fig. 6) show the<br />
appearance in the lake <strong>of</strong> this organism from 1986.<br />
Overall copepod biomass (g m -2 ) over the study period is shown in Fig. 7a. <strong>The</strong><br />
Copepoda make up approximately 35% <strong>of</strong> total zooplankton biomass. E. <strong>drieschi</strong><br />
contributes less than 3% to the total zooplankton biomass (Fig. 7b).
25<br />
Monthly Copepod Biomass<br />
25.0<br />
20.0<br />
15.0<br />
10.0<br />
5.0<br />
0.0<br />
Jan-96<br />
Apr<br />
Jul<br />
Oct<br />
Jan-97<br />
Apr<br />
Jul<br />
Oct<br />
Jan-98<br />
Apr<br />
Jul<br />
Oct<br />
Jan-99<br />
Apr<br />
Jul<br />
Oct<br />
Jan-00<br />
Apr<br />
g -1 m 2<br />
Jul<br />
Oct<br />
a.)<br />
Contribution <strong>of</strong> E. <strong>drieschi</strong> biomass to Total Zooplankton<br />
Biomass<br />
2.4%<br />
2.0%<br />
1.6%<br />
1.2%<br />
0.8%<br />
0.4%<br />
0.0%<br />
b.)<br />
Figure 7: a) Total monthly copepod biomass (g/m 2 ) in L. Kinneret.<br />
b) Percent E. <strong>drieschi</strong> biomass to total zooplankton biomass.<br />
E. <strong>drieschi</strong> does not produce identifiable cohorts, but reproduces continuously<br />
throughout the months it is found in the water column (Dec-Jul) as indicated by the rate<br />
<strong>of</strong> change (Fig. 8a). Instantaneous birth rate (b) is quite similar to instantaneous death<br />
rate (d) shown in Figs, 8b, c. <strong>The</strong> calculated instantaneous rate <strong>of</strong> change is small, thus<br />
giving the population the appearance <strong>of</strong> being in “steady-state”.<br />
Daily secondary production (biomass accumulated per unit time) to biomass was<br />
calculated for the years 1996-98. <strong>The</strong> P/B ratios for cyclopoid copepods in the Kinneret<br />
range from: 0.10-0.16. <strong>The</strong> P/B ratios <strong>of</strong> E. <strong>drieschi</strong> from 1996-97 show a slightly higher<br />
secondary production rate with a decline beginning in 1998 (Fig. 9a-d). Ratios <strong>of</strong> 0.1-<br />
0.22 have been found for species <strong>of</strong> Diaptomus in eutrophic lakes (Ponyi et al 1982).
26<br />
Rate <strong>of</strong> Change<br />
0.300<br />
0.200<br />
0.100<br />
0.000<br />
-0.100<br />
-0.200<br />
-0.300<br />
a).<br />
b).<br />
Instantaneous Birth rate<br />
4.0<br />
3.0<br />
2.0<br />
1.0<br />
0.0<br />
Jan-96<br />
Apr-96<br />
Jul-96<br />
Oct-96<br />
Jan-97<br />
Apr-97<br />
Jul-97<br />
Oct-97<br />
Jan-98<br />
Apr-98<br />
Jul-98<br />
Oct-98<br />
Jan-96<br />
Apr-96<br />
Jul-96<br />
Oct-96<br />
Jan-97<br />
Apr-97<br />
Jul-97<br />
r = ln(N t - lnN 0 ) / t<br />
Oct-97<br />
Jan-98<br />
Apr-98<br />
Jul-98<br />
Oct-98<br />
Instantaneous Death Rate<br />
3.0<br />
d = b - r<br />
1.5<br />
0.0<br />
Jan-96<br />
Mar-96<br />
May-96<br />
Jul-96<br />
Sep-96<br />
Nov-96<br />
Jan-97<br />
Mar-97<br />
May-97<br />
Jul-97<br />
Sep-97<br />
Nov-97<br />
Jan-98<br />
Mar-98<br />
May-98<br />
Jul-98<br />
Sep-98<br />
Nov-98<br />
b = ln (1 + B)<br />
c).<br />
Figure 8: a) Rate <strong>of</strong> change (r), b) Instantaneous death rate (d), c) Instantaneous<br />
birth rate (b) for E. <strong>drieschi</strong> population in Lake Kinneret.
E. <strong>drieschi</strong> has a strong seasonal periodicity (Figs. 10a-c). <strong>The</strong> population begins to<br />
appear in mid-winter (late December/January), and continues to increase throughout<br />
winter into spring. <strong>The</strong> population reaches peak abundance in April-May,<br />
after which numbers decline through June. By the end <strong>of</strong> June/July, numbers have<br />
declined to the point <strong>of</strong> being undetectable with routine sampling methods (< 0.03/ m 3 ).
Total E. <strong>drieschi</strong> biomass ( mg / m 3 )<br />
120<br />
100<br />
80<br />
60<br />
40<br />
20<br />
0<br />
1994<br />
Daily<br />
P / B = 0.33<br />
50<br />
45<br />
40<br />
35<br />
30<br />
25<br />
20<br />
15<br />
10<br />
5<br />
0<br />
Net biomass Production (mg / m 3 /<br />
d)<br />
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec<br />
Total E. <strong>drieschi</strong> biomass ( mg / m 3 )<br />
600<br />
500<br />
400<br />
300<br />
200<br />
100<br />
0<br />
1996<br />
Daily<br />
P / B = 0.22<br />
140<br />
120<br />
100<br />
80<br />
60<br />
40<br />
20<br />
0<br />
Net biomass Production (mg / m 3 /<br />
d)<br />
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec<br />
450<br />
80<br />
Total E. <strong>drieschi</strong> biomass ( mg / m 3 )<br />
400<br />
350<br />
300<br />
250<br />
200<br />
150<br />
100<br />
50<br />
1997<br />
Daily<br />
P / B = 0.20<br />
70<br />
60<br />
50<br />
40<br />
30<br />
20<br />
10<br />
Net biomass Production (mg / m 3 / d)<br />
Total E. <strong>drieschi</strong> biomass ( mg / m 3 )<br />
0<br />
180<br />
160<br />
140<br />
120<br />
100<br />
80<br />
60<br />
40<br />
20<br />
0<br />
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec<br />
1998<br />
Daily<br />
P / B = 0.12<br />
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec<br />
40<br />
35<br />
30<br />
25<br />
20<br />
15<br />
10<br />
5<br />
0<br />
0<br />
Net biomass Production (mg / m 3 / d)<br />
Figure 9: Seasonal Productivity / Biomass ratios (P/B) for E. <strong>drieschi</strong> in<br />
L. Kinneret for the years 1994, 1996-1998.
Total Number <strong>of</strong> Organisms, L -1<br />
80<br />
70<br />
60<br />
50<br />
40<br />
30<br />
20<br />
10<br />
0<br />
1996<br />
30<br />
26<br />
22<br />
18<br />
14<br />
10<br />
Average Water Temperature ( 0 C)<br />
a.)<br />
Jan<br />
Feb<br />
Apr<br />
May<br />
Total Number <strong>of</strong> Organisms, L -1<br />
Jul<br />
Sep<br />
Nov<br />
40<br />
35<br />
30<br />
25<br />
20<br />
15<br />
10<br />
5<br />
1997<br />
30<br />
26<br />
22<br />
18<br />
14<br />
Average Water Temperature ( 0 C)<br />
b.)<br />
0<br />
Jan<br />
Jan<br />
Feb<br />
Feb<br />
Mar<br />
Mar<br />
Apr<br />
Apr<br />
M…<br />
M…<br />
Jun<br />
Jul<br />
Jul<br />
Jul<br />
Aug<br />
Sep<br />
Sep<br />
Oct<br />
Oct<br />
Nov<br />
Dec<br />
10<br />
1998<br />
c.)<br />
Total Number <strong>of</strong> Organisms, L -1<br />
12<br />
10<br />
8<br />
6<br />
4<br />
2<br />
0<br />
Jan<br />
Feb<br />
Mar<br />
May<br />
Jul<br />
Sep<br />
Oct<br />
Average Water Temperature ( 0 C)<br />
30<br />
26<br />
22<br />
18<br />
14<br />
10<br />
Figure 10: a. – c.) Seasonal periodicity <strong>of</strong> E. <strong>drieschi</strong> at Station F,<br />
1996 – 98.
Reproduction is continuous throughout the period that E. <strong>drieschi</strong> occurs in the<br />
water column, as seen by the presence <strong>of</strong> nauplii, copepodites, and both sexes in all<br />
samples. Number <strong>of</strong> eggs per clutch varies greatly (8-26). <strong>The</strong> highest number <strong>of</strong> eggs<br />
per female occurs in Jan./Feb. (16-22). (One female, sampled in February, was found<br />
carrying a clutch <strong>of</strong> 66 eggs.) <strong>The</strong> number <strong>of</strong> females carrying eggs increases in spring<br />
with an average clutch size <strong>of</strong> 12-18. Total annual biomass averaged between 1-1.4<br />
mg/ l (wet weight). <strong>The</strong> greatest biomass occurred in the spring with values reaching<br />
2.01 mg/l (wet weight). Figure 11 shows the percentage <strong>of</strong> egg bearing females present<br />
in the water column plotted with average water temperature (r 2 = 0.56, P5) in relation to Lake<br />
Temperature, 1997 - 98<br />
Females with eggs (%)<br />
100%<br />
80%<br />
60%<br />
40%<br />
20%<br />
0%<br />
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec<br />
28<br />
26<br />
24<br />
22<br />
20<br />
18<br />
16<br />
14<br />
Lake Temperature<br />
12<br />
10<br />
Figure 11: Seasonality <strong>of</strong> egg-carrying adult female E. <strong>drieschi</strong> (percent <strong>of</strong> total<br />
females) versus lake temperature (1997-1998)<br />
<strong>The</strong>re was a tendency for individuals to occur at greater depths as the seasons<br />
progressed. By early to mid summer, very low numbers <strong>of</strong> organisms were found in the<br />
upper water column (
decline <strong>of</strong> E. <strong>drieschi</strong> in the water column, and increasing salinity (Fig. 12a), and<br />
increasing temperature (r 2 = 0.75, P
3.3 Sex Ratio<br />
<strong>The</strong> ratio <strong>of</strong> adult females to males is given in Table 2 .<strong>The</strong> years 1995-97 showed a<br />
slightly male biased sex ratio (P
Average Depth <strong>of</strong> Individual = x 1 z 1 + x 2 z 2 + ….+ x n z n (10)<br />
x 1 + x 2 + …x n<br />
where z 1 is depth 1 and z 2 is depth 2, x 1 is the number <strong>of</strong> individuals at depth 1, x 2 is the<br />
number <strong>of</strong> individuals at depth 2 and so on to depth n (Wetzel 1991). Table 3 gives the<br />
average depth distributions for the spring 24 hour survey:<br />
Table 3: Average depth distribution <strong>of</strong> E. <strong>drieschi</strong> life stages, Station F, Spring survey, April 1997<br />
----------------------------------------------------------------------------------------------------------<br />
Day<br />
Mean Depth Distribution (m)<br />
-----------------------------------------------------------------------------------------------<br />
Adults 13.48<br />
Juveniles 8.26<br />
Nauplii 9.62<br />
--------------------------------------------------------------------------------------------------------<br />
Night<br />
Mean Depth Distribution (m)<br />
--------------------------------------------------------------------------------------------------<br />
Adults 7.50<br />
Juveniles 5.72<br />
Nauplii 8.76<br />
----------------------------------------------------------------------------------------------------------<br />
Spring temperature pr<strong>of</strong>iles showed an average temperature difference <strong>of</strong> 3 0 C from<br />
surface to bottom. <strong>The</strong> lake is mixed with no distinct thermocline. Chlorophyll<br />
concentrations (g/l Chl) show maximums during full daylight in the upper depths.<br />
Nanoplankton (20 m) plankton in the<br />
water column. Oxygen pr<strong>of</strong>iles are typical for the season. Average Secchi depth was<br />
2.42 meters, and visible light diminished below 5 meters depth.
An ANOVA analysis <strong>of</strong> spring abiotic parameters versus organism density showed a<br />
significant effect (P
Resting Egg Distribution in the<br />
Sediments 1997 - 98<br />
Percent <strong>of</strong> total number eggs<br />
0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%<br />
1<br />
2<br />
3<br />
Sediment Depth (cm)<br />
4<br />
5<br />
6<br />
7<br />
8<br />
9<br />
10<br />
11<br />
12<br />
Figure 13: Vertical distribution <strong>of</strong> resting eggs in the sediments at Station F for<br />
1997 (cross fill), 1998 (solid fill).<br />
E. <strong>drieschi</strong> produces two distinct types <strong>of</strong> eggs: subitaneous (immediately hatching ),<br />
and diapausing (benthic resting) egg (Figs. 14a, b). <strong>The</strong> presence <strong>of</strong> an “extravitelline<br />
space” in the subitaneous eggs <strong>of</strong> preserved E. <strong>drieschi</strong> can be detected, in most cases,<br />
without the use <strong>of</strong> the Lugol’s solution stain (Lohner et al. 1990). <strong>The</strong> type <strong>of</strong> eggs<br />
carried by live females can be distinguished when viewed against a light background<br />
(Fig 14b). <strong>The</strong>re are no outstanding morphological features <strong>of</strong> the eggs when viewed<br />
with a scanning electron microscope (Figs 14c, 15 a-b).
Over 80% <strong>of</strong> the resting eggs in the upper sediment layers were viable and hatched out<br />
after incubation, but those from the lower layers were less abundant and in poorer<br />
condition. Resting eggs that did not hatch within 14 days <strong>of</strong> incubation were considered<br />
infertile. Eggs that were damaged or deteriorated did not hatch.<br />
Female E. <strong>drieschi</strong> produce eggs continuously throughout the entire period they are<br />
found in the water column <strong>of</strong> the Kinneret. Large clutches (>22 eggs clutch –1 ) <strong>of</strong><br />
subitaneous eggs are produced in the early part <strong>of</strong> the season (Jan-Mar) as the water<br />
begins to warm (15.9-17.0 0 C). By mid-April–May, resting eggs make up about 33.5%<br />
<strong>of</strong> total eggs produced and clutch sizes range from 8-22. Production <strong>of</strong> diapausing eggs<br />
increases to about 50% <strong>of</strong> total eggs from May to June when the water temperature<br />
ranges from 18-23 0 C. Subitaneous and diapausing eggs were never observed together in<br />
the same clutch. <strong>The</strong> size <strong>of</strong> the eggs within each clutch is varied. <strong>The</strong> average size <strong>of</strong><br />
subitaneous eggs is 0.142 (+ 0.04) mm (n=300), and diapause eggs 0.153 (+ 0.04) mm<br />
(n= 250).<br />
37<br />
a)
)<br />
c)<br />
Figure 14: (a) resting egg from sediments (0.153 mm), (b) subitaneous egg from<br />
live egg-bearing female (0.140 mm), (c) detail resting egg from sediment<br />
(SEM x 2000)
a).<br />
b).<br />
Figure 15: a). Resting egg extracted from bottom sediments (distortion from<br />
drying process). b). Subitaneous egg from clutch <strong>of</strong> adult female (distortion from<br />
drying process).
3.6 Development<br />
Development Time<br />
Development time (number <strong>of</strong> days required) <strong>of</strong> <strong>Eudiaptomus</strong> <strong>drieschi</strong> life stages at<br />
the different experimental temperatures are shown in Table 4. It can be seen that<br />
development times are longer in animals that were reared at low temperatures, than<br />
those reared at higher temperatures This is compatible with previous work by Geiling<br />
and Campbell 1972, Landry 1975, Kamps 1978, Ban 1994, and Klein Breteler et al.<br />
1994. E. <strong>drieschi</strong> reared at high temperatures (>24 0 C), did not produce eggs, became<br />
covered in fungus and died.<br />
Table 4: Mean stage development time in days (average percent) with standard deviations <strong>of</strong><br />
<strong>Eudiaptomus</strong> <strong>drieschi</strong> at experimental temperatures, (N=19,20)<br />
Temperature 12 0 C 15 0 C 18 0 C 22 0 C<br />
egg 10.60 (3.89) 4.58 (1.24) 1.11 (0.24) 0.85 (0.09)<br />
NI 2.65 (0.46) 1.71 (0.55) 0.88 (0.10) 0.93 (0.10)<br />
NII 3.18 (0.66) 1.74 (0.54) 1.23 (0.34) 1.00 (0.19)<br />
NIII 3.18 (0.59) 1.78 (0.44) 1.29 (0.30) 1.24 (0.26)<br />
NIV 3.25 (0.73) 1.72 (0.48) 1.33 (0.41) 1.33 (0.32)<br />
NV 3.13 (0.86) 1.79 (0.48) 1.60 (0.50) 1.32 (0.29)<br />
NVI 3.23 (0.61) 1.84 (0.24) 1.56 (0.37) 1.48 (0.40)<br />
CI 2.50 (0.85) 1.65 (0.40) 1.05 (0.33) 0.92 (0.17)<br />
CII 2.95 (0.68) 2.04 (0.70) 1.42 (0.30) 0.95 (0.21)<br />
CIII 2.95 (0.69) 2.05 (0.55) 1.45 (0.30) 1.06 (0.24)<br />
CIV 3.03 (0.51) 2.15 (0.73) 1.51 (0.41) 1.10 (0.28)<br />
CV 3.11 (0.93) 2.36 (0.74) 1.68 (0.43) 1.15 (0.25)<br />
<strong>The</strong>re were clear differences in duration <strong>of</strong> embryonic development at low temperatures.<br />
Duration was longest (10.6 + 3.89 days) at 12 0 C.<br />
Development times ranged from 4.58 + 1.2, 1.11 + 0.24 and 0.85 +0.09 days for 15,<br />
18 and 22 0 C respectively. As temperature increased, eggs developed more rapidly; day<br />
at 22 0 C. Early naupliar (NI-NIII), and copepodite stages (CI-III) have shorter (p
duration <strong>of</strong> naupliar stages from copepodite stages, but a general trend in postembryonic<br />
development across the different temperatures was seen for all treatments. In<br />
many species, nauplii develop somewhat faster than copepodites, however it has been<br />
shown that at optimal temperature and food conditions, stage duration can be very<br />
similar (Fig. 15). <strong>The</strong> data show a very gradual increase in development time from NII<br />
through NV with a slight drop at NVI. Development time in copepodites is seen to<br />
increase, generally, from CI to CV.<br />
13%<br />
Stage Duration (%)<br />
11%<br />
9%<br />
7%<br />
5%<br />
NI NII NIII NIV NV NVI CI CII CIII CIV CV<br />
Stage<br />
Figure 15: Relative stage duration <strong>of</strong> E. <strong>drieschi</strong>.<br />
In Lake Kinneret, average yearly temperature ranges from 14 to 28.5 0 C. At optimal<br />
temperatures, (18-20 0 C) females can produce eggs within 24 hours <strong>of</strong> mating.<br />
Subsequent clutches are produced within 1-1.5 days (+ 0.45) at 18 0 C. Under low<br />
temperature conditions, females can take up to 2.5 days to produce eggs. At<br />
temperatures >23 0 C, females were not seen to produce eggs. E. <strong>drieschi</strong> is more<br />
commonly found in waters with temperatures that range from 7-22 0 C (Kiefer, 1968,<br />
Beeton 1981, Gunduz 1998). During the summer months when, water temperatures in<br />
the Kinneret can reach 30 0 C in the epilimnion E. <strong>drieschi</strong> is absent from the upper<br />
water column and if at all present, found only in the metalimnion (>10 m depth) where<br />
the temperature is less than 20 0 C.
Development Rate<br />
Post-embryonic development rates (amount <strong>of</strong> development per day) at the different<br />
experimental temperatures are shown in Figures 16 and 17. It can be seen that naupliar<br />
development rate proceeds fairly linearly at lower temperatures (
Specific length growth rate<br />
Specific growth rates in relation to temperature can be seen in Fig. 18.<br />
1.5<br />
y = 0.1063x - 0.7525<br />
R² = 0.9971<br />
C L (T)/C L (St)<br />
1<br />
0.5<br />
0<br />
5 10 15 20 25<br />
Temperature<br />
Figure 18: Specific length growth rate (C L ) <strong>of</strong> each life stage at a given temperature<br />
(T), in relation to intrinsic length growth rate (C L (St)).<br />
Specific length growth rates (C L ) <strong>of</strong> life history stages at any two temperatures were<br />
highly correlated (r 2 >0.9, p
3.7 Salinity tolerance<br />
Survival <strong>of</strong> <strong>Eudiaptomus</strong> at the different experimental salinities and temperatures is<br />
shown in Table 5.<br />
Table 5: Results <strong>of</strong> ANOVA analysis <strong>of</strong> effects <strong>of</strong> different salinity concentrations on the survival <strong>of</strong><br />
E. <strong>drieschi</strong>.<br />
---------------------------------------------------------------------------------------------------------<br />
Salinity Effect Temperature P value<br />
--------------------------------------------------------------------------------------------------------<br />
Males<br />
18 o C<br />
High vs. Low
higher tolerance for colder temperatures at medium and low salinities. It was found that<br />
at low temperatures (0.001) greater percent <strong>of</strong> adult females survived at the higher food<br />
concentration. Since nanaplankton concentrations in the Kinneret can reach as low as 9.8<br />
x 10 3 cells ml –1 , wild populations <strong>of</strong> E <strong>drieschi</strong> may be able to utilize alternative food<br />
sources that would enable them to survive at very low food concentrations. However, at<br />
low concentrations <strong>of</strong> a uni-algal diet, percent survival is reduced.
4. Discussion<br />
4.1 Taxonomical Position<br />
Upon examining the original material <strong>of</strong> H. Driesch from the Hamburg Museum<br />
collection (1935), Kiefer declared that E. <strong>drieschi</strong> was closely affiliated to E. vulgaris. In his<br />
revision <strong>of</strong> the genus, Kiefer (1968) described 6 forms <strong>of</strong> E. <strong>drieschi</strong> from different<br />
geographic locations; Yugoslavia (Montenegro), Corfu, Turkey, and Ceylon (Sri Lanka). He<br />
wrote that the distribution <strong>of</strong> E. <strong>drieschi</strong> included the Mediterranean region <strong>of</strong> the Palearctic<br />
and, 6 0 North <strong>of</strong> the equator in the tropics. He considered this to be a very unusual<br />
geographic distribution <strong>of</strong> Diaptomids. Kiefer suspected that the specimen from Ceylon (Sri<br />
Lanka), was not actually E. <strong>drieschi</strong>, but indeed, a different species. <strong>The</strong> specimen from<br />
Ceylon was taken from fish ponds, where temperatures are considerably high (29-36 0 C,<br />
www. EDRC/ Statistics). <strong>The</strong> present research study showed categorically, that E. <strong>drieschi</strong><br />
does not tolerate high (tropical) temperatures and would then confine E. <strong>drieschi</strong>’s<br />
distribution to Anatolia and the Levant (Dumont 1994). Based on drawings <strong>of</strong> the material,<br />
there are similarities in the structures <strong>of</strong> the male right antenna and the P 5 leg as well as the<br />
positioning <strong>of</strong> spines on the female last thoracic and genital segments, between the Kinneret<br />
form and those specimens which are found in Corfu. Based on these morphological<br />
similarities, it is highly reasonable to infer that this species may have originally been brought<br />
to the Kinneret via migrating water birds.<br />
E. <strong>drieschi</strong> from the Kinneret can be distinguished from other species <strong>of</strong> <strong>Eudiaptomus</strong><br />
primarily by the P 5 appendages <strong>of</strong> the 2 sexes, and the male antenna.<br />
E. <strong>drieschi</strong> has a short endopod as opposed to the long, stout endopod <strong>of</strong> the male right P 5<br />
found in E. gracilis (Sars 1863) whose range includes most <strong>of</strong> Europe, Great Britain, and<br />
Russia. <strong>The</strong> endopod <strong>of</strong> the female right P 5 E. gracilis is covered with an apical fringe <strong>of</strong><br />
hairs while that <strong>of</strong> E. <strong>drieschi</strong> is not. <strong>The</strong> distal corner process <strong>of</strong> the second exopod <strong>of</strong> male
left P 5 E. <strong>drieschi</strong> is blunter (rounded) with a sharp inner process. In E. gracilis, the distal<br />
process is sharper and the inner process has feather-like setae near the terminus. E. vulgaris<br />
(Schmeil 1898) which is found throughout Europe, Russia, central Asia, and northern Africa,<br />
has a hyaline membrane laying obliquely to the P 5 basipod, as well as a sharp projection from<br />
the outer distal corner <strong>of</strong> the first exopod. In E. <strong>drieschi</strong>, the hyaline membrane is parallel,<br />
and the projection from the outer distal corner <strong>of</strong> the first exopod is blunter. A newly<br />
described, closely related species, E. anatolicus n. sp., found in Turkey (Gunduz 1999),<br />
differs from E. <strong>drieschi</strong> in the absence <strong>of</strong> a “semicircular chitinous plate on the distal inner<br />
corner” <strong>of</strong> the coxopod <strong>of</strong> the male right P 5.<br />
Biometrics<br />
Kiefer (1935) described E. dreischi adult body length for males as 1.02-1.05 mm<br />
with a maximum 1.60 mm, and females as 1.17-1.20 mm with a maximum<br />
1.70 mm. <strong>The</strong> mean body length value (1.14mm) <strong>of</strong> adult male <strong>Eudiaptomus</strong> from Lake<br />
Kinneret is somewhat larger than the average values given by Kiefer (1935) but well<br />
within his range. It is known that body length <strong>of</strong> adult copepods can vary during a<br />
season, because temperature and food availability influence growth and adult body size.<br />
Elmore (1982) showed experimentally that body length <strong>of</strong> adult Diaptomus dorsalis<br />
(Marsh) increased at high food concentrations (10 x 10 4 cells /ml, Chlamydomonas).<br />
<strong>The</strong>re is evidence that copepod body size decreases with increasing temperatures (Jacobs<br />
& Bouwhuis 1978, Kamps 1978, Hopcr<strong>of</strong>t 1998, Gillooly 2000).
4.2 Ecological Implications <strong>of</strong> Development<br />
In copepod populations that have more than 1 generation per year, it is laborious to<br />
determine production values in situ. <strong>The</strong> presence <strong>of</strong> several generations at any one time<br />
makes it necessary to experimentally determine stage development times in the lab. <strong>The</strong><br />
development cycles <strong>of</strong> calanoid and cyclopoid species have long been the subject <strong>of</strong><br />
intense and varied studies (Gophen 1976, Ban 1991, 1992, 1992a, 1994, Chen 1993,<br />
Davis 1992, Durbin 1992). Knowledge <strong>of</strong> an organisms’ developmental history enables<br />
us to understand their population dynamics as well as intra-species relationships under<br />
natural conditions (Kawabata 1989, Atkinson 1991, Giangrande 1994, Kiorboe 1994,<br />
Toth 1996). Variations in life cycle patterns (sex ratios, P/B ratios, body size) may<br />
indicate adaptations to environmental changes such as predation pressure, food<br />
availability or abiotic factors like temperature and salinity (Allan 1976). Food type and<br />
quality as well as temperature and photo-periodicity affect the life span and stage<br />
development times <strong>of</strong> zooplankton species (Bogdon & McNaught 1975, Gophen 1976,<br />
Bergmans 1984, Santer 1994, Watson 1984, Burns & Hegarty 1994). A species’ life<br />
cycle may respond and adjust to seasonal differences in temperature and day-length<br />
(Hairston Jr. 1990, 1995, Hairston & Olds 1986).<br />
<strong>The</strong> instantaneous rate <strong>of</strong> change <strong>of</strong> the E. <strong>drieschi</strong> population in the Kinneret is<br />
small, which supports the observation that distinct cohorts cannot be distinguished from<br />
the weekly sampling series. <strong>The</strong> instantaneous birth rate is very similar to the<br />
instantaneous death rate (mortality), indicating the population is in a “steady state” for<br />
the period <strong>of</strong> time (approx. 6 months) it can be found in detectable numbers.<br />
It is worth noting that in Lake Skadar, Montenegro, E. <strong>drieschi</strong> exhibits rapid<br />
turnover and almost continuous reproduction and mortality, as it does in the Kinneret.<br />
However, no pattern <strong>of</strong> seasonality was observed. It occurs throughout the year with
peak abundance in October where water temperatures vary from 15- 18 0 C (Petkovic<br />
1981), not during winter/spring as in the Kinneret when water temperatures are low<br />
(16-20 0 C).<br />
Upon hatching from the egg, diaptomid copepods pass through 6 naupliar (NI – NVI)<br />
and 5 copepodite (CI – CV) stages during their development to adulthood. <strong>The</strong>y undergo<br />
periods <strong>of</strong> intense metabolic activity prior to these molts (Carrillo 2001). Naupliar stage<br />
NI , (and in some species, NII & NIII ) is a non-feeding stage (Burns 1988, Hart 1990),<br />
and therefore more influenced by temperature than food concentration. <strong>The</strong>se stages also<br />
suffer high mortality (Elmore 1983, Ban 1994, Kawabata 1995, Gillooly 2000). Each<br />
developmental stage shows a specific response to environmental conditions by its varied<br />
feeding habits, locomotion, vertical distribution, and rate <strong>of</strong> mortality. Determining the<br />
development, growth and survival <strong>of</strong> post-embryonic life stages is necessary to analyze<br />
the dynamics <strong>of</strong> the natural populations. Development times <strong>of</strong> diaptomid life stages<br />
have been shown to be temperature and food dependant (Kawabata 1989, Hart 1990,<br />
Ban 1994). Geiling (1972) found development times for Diaptomids varied as much as<br />
66.2 days at low temperatures, to 14.6 days at high temperatures. Hamberger (1987)<br />
found development time <strong>of</strong> E. graciloides from N I to adult to be 23 days at 21 0 C and<br />
42 days at 14.5 0 C. Similar development times were found for E. gracilis (P-Zankai<br />
1978). Similar to those studies, E. <strong>drieschi</strong> from the Kinneret also showed increasing<br />
development with temperature (12 days at 22 0 C and 33 days at 12 0 C from N I to adult).<br />
Gillooly (2000) states that generation time is related to both temperature and adult body<br />
mass. In a review <strong>of</strong> post-embryonic development duration <strong>of</strong> calanoid copepods, Hart<br />
(1990) found ratios <strong>of</strong> duration <strong>of</strong> copepodid development to duration <strong>of</strong> naupliar<br />
development (Dc/Dn) to favor slightly longer duration <strong>of</strong> the larger copepodid stages<br />
regardless <strong>of</strong> temperature. Knowledge <strong>of</strong> this relationship could aid in explaining
seasonal abundance or intra-specific interactions. <strong>The</strong> post-embryonic development<br />
times <strong>of</strong> the Kinneret population <strong>of</strong> E. <strong>drieschi</strong> are very similar, however there are<br />
differences in development times between stages.<br />
Ontogenetic development <strong>of</strong> E. <strong>drieschi</strong> in Lake Kinneret is similar to the patterns<br />
described in the literature for other diaptomids, and highly influenced by temperature.<br />
<strong>The</strong> early stages (NI-NIII) have relatively short development times, but development<br />
times are seen to increase to N IV. <strong>The</strong> stages that undergo the more complex changes<br />
(NVI & CIV) have slightly longer mean development times. That these development<br />
times are highly influenced by environmental parameters is reflected in the seasonal<br />
abundance and the changing P/B ratios.<br />
Production/Biomass Ratios<br />
Changes in the male/female sex ratios are also indicative <strong>of</strong> changes in population<br />
dynamics. Biased ratios, which are more the rule than the exception in freshwater, may<br />
be the result <strong>of</strong> changes in rates <strong>of</strong> development or mortality <strong>of</strong> the different sexes<br />
(Hairston et al. 1983). Ponyi (1982) found a sex ratio <strong>of</strong> 1:1.6 in favor <strong>of</strong> female E.<br />
gracilis in Lake Balaton at the start <strong>of</strong> their study period, which changed the following<br />
year to 1:1.1 in favor <strong>of</strong> males. Maly (1970) showed that selective predation on adult<br />
copepods caused skewed sex ratios. Although E. <strong>drieschi</strong> has been found in the guts <strong>of</strong><br />
zooplanktivorous fish (Gophen 1978, Shapiro 1999) it is doubtful that selective<br />
predation is a causative factor in the dynamics <strong>of</strong> this organism in the Kinneret because<br />
<strong>of</strong> its low density. <strong>The</strong> <strong>Eudiaptomus</strong> population structure was found to favor females in<br />
1994, males from 1995-97, and a 1:1 sex ratio was seen in 1999. Males were found to<br />
develop slightly faster than females in the laboratory, which could account for their
higher numbers. <strong>The</strong> shift in sex ratio is another indication <strong>of</strong> the instability <strong>of</strong> the E.<br />
<strong>drieschi</strong> population in the Kinneret.<br />
Within the study period, the population density varied from 43 ind. l -1 in 1997, to<br />
distinguish resting eggs from subitaneous ones by the presence <strong>of</strong> a space between the<br />
embryo and the chorion in the subitaneous eggs.<br />
<strong>The</strong> resting eggs may also provide a means for dispersal as well as being an energy<br />
saving trait to remain in a specific location (Dahms 1995, Hairston Jr. 1996). Jarnagin et<br />
al. (2000) found that fish act as dispersing agents <strong>of</strong> diapausing invertebrate eggs in their<br />
movements between the pelagic and littoral zones <strong>of</strong> lakes. Viable resting eggs <strong>of</strong> E.<br />
<strong>drieschi</strong> were found in the gut <strong>of</strong> larval catfish (Clarias gariepinus) from the Kinneret,<br />
however their role in the dispersal <strong>of</strong> <strong>Eudiaptomus</strong> resting eggs has yet to be<br />
investigated.<br />
Many species <strong>of</strong> marine planktonic copepods have been shown to produce resting or<br />
diapause eggs as a long-term survival strategy (Marcus 1996). Such strategies are<br />
considered unusual for temperate climates that do not exhibit extreme seasonal<br />
fluctuations. However, examples from tropical and sub-tropical areas have been<br />
recorded. <strong>The</strong>se species usually disappear from the water column for some months, but<br />
the populations recover from resting eggs in the sediment (Marcus 1989). Benthic<br />
resting eggs may be an important source <strong>of</strong> recruitment to the plankton. <strong>The</strong>y do not<br />
utilize benthic food resources, but they may add a potential prey item for benthic<br />
consumers.<br />
E. <strong>drieschi</strong> in Lake Kinneret follows a seasonal pattern characteristic <strong>of</strong> sub- tropical<br />
diaptomid populations. <strong>The</strong>y became very scarce in the water column throughout the<br />
summer/fall seasons, while the population has a higher density throughout the<br />
winter/spring. Subitaneous eggs are produced in Jan-Mar., then the first clutches <strong>of</strong><br />
resting eggs are produced. In April-May the percentage <strong>of</strong> resting eggs increases to<br />
about 33% <strong>of</strong> all eggs produced. Throughout May-June, resting eggs make up<br />
approximately 50% <strong>of</strong> all eggs produced. During this period, the water temperature in<br />
the epilimnion is increasing (Fig. 6). It was found experimentally, that temperatures<br />
above 24 0 C are lethal to E. <strong>drieschi</strong> in the Kinneret., Although development rates are<br />
high at temperatures > 22 0 C, egg production is greatly reduced, thus bringing about the<br />
annual population decline.<br />
<strong>The</strong> source <strong>of</strong> the recovered winter/spring populations in the Kinneret are the resting<br />
eggs produced the previous season. Ban (1992) found viable eggs <strong>of</strong> the freshwater<br />
diaptomid, Eurytemora affinis (<strong>Poppe</strong>) distributed up to sediment depths <strong>of</strong> 10 cm., with<br />
the majority found in the upper 5 cm. Hatching <strong>of</strong> these eggs in the lab was inhibited by
covering them with a layer <strong>of</strong> sediment, which could explain the accumulation <strong>of</strong> viable<br />
eggs at greater sediment depths. This finding eliminates photoperiod as a cue for<br />
inducing or terminating diapause (Ban 1992, Ban & Minoda 1992, Hairston Jr. &<br />
Kearns 1995). <strong>The</strong> maximum sediment depth at which the resting eggs <strong>of</strong> E. <strong>drieschi</strong> in<br />
the Kinneret were found was 15 cm. Eggs were seen to be viable when induced to hatch<br />
in the laboratory, by removal from the sediments. All eggs did not hatch simultaneously,<br />
but over a period <strong>of</strong> weeks. It is assumed that this reflects the order in which they were<br />
laid down.<br />
Resting eggs that are covered by sediment will not hatch. Recent studies have shown<br />
that the accepted rate <strong>of</strong> sedimentation in the Kinneret (mean 0.5 cm./yr.) actually varies<br />
highly with location (Serruya 1978). Presence <strong>of</strong> eggs, coincides reasonably with the<br />
timing <strong>of</strong> their appearance among the pelagic lake zooplankton. Nishri et al. (1998) have<br />
successfully dated sediment layers using 137 Cs activity. <strong>The</strong>y have shown that from the<br />
pelagic regions, (station A, 42 m depth), sedimentation rate is about 3-4 mm per year.<br />
<strong>The</strong>refore it is reasonable to infer that resting eggs found at sediment depths <strong>of</strong> 9- 10 cm<br />
were deposited in the early ‘80’s (1982-1984). Sedimentation rate at sampling station F<br />
(20 m depth) is roughly 50 % higher than station A so that resting eggs found at depths<br />
<strong>of</strong> 10-12 cm were most likely deposited in the mid to late ‘80’s. Those eggs in the<br />
deeper sediment layers act as a stock <strong>of</strong> potential recruits to the planktonic population.<br />
Bioturbation may play a role in exposing the eggs lying under the water-sediment<br />
interface. Bottom feeding fishes or bubbles <strong>of</strong> gas (methane) may disturb the upper<br />
sediment layers, exposing the eggs and allowing them to hatch.<br />
4.4 Vertical Distribution<br />
<strong>The</strong> vertical diel migration <strong>of</strong> a zooplankton species should be differentiated from its<br />
ontogenetic vertical distribution. <strong>The</strong> species show a tendency to be found in deeper<br />
layers <strong>of</strong> the water column during the daylight hours, while their numbers are more<br />
evenly distributed at night. Kawabata (1995) found significant differences in vertical<br />
depth distributions between life stages <strong>of</strong> Eodiaptomus japonicus in Lake Biwa, Japan.<br />
E. japonicus ascended in the early naupliar stages (NI – NIII) and descended in the later<br />
stages (NIV – CII). This could be explained by the developmental changes in swimming
ability as copepods mature. Diaptomid nauplii have poor swimming ability, with no<br />
developed trunk appendages. Early copepodites have not yet developed the five pairs <strong>of</strong><br />
swimming legs, thus are also poor swimmers compared to later copepodite stages and<br />
adults.<br />
<strong>The</strong>re is no difference between the day and night vertical distribution <strong>of</strong> the naupliar<br />
stages <strong>of</strong> E. <strong>drieschi</strong> in the Kinneret, they remain more or less around the same depth (8-<br />
9 m). Copepodids were observed to inhabit similar depths to those <strong>of</strong> nauplii during the<br />
day, but were found at slightly shallower depths (5-6 m) throughout the night. Adults<br />
were distributed primarily at depths
4.5 Experimental Results<br />
4.5.1 Salinity<br />
<strong>The</strong> period 1970-1987 was characterized by a number <strong>of</strong> man-made changes in the<br />
Lake Kinneret ecosystem (Gophen 1992). <strong>The</strong> Degania dam at the southern end <strong>of</strong> the<br />
lake was built in 1932 and caused an overall increase <strong>of</strong> the water level. <strong>The</strong> National<br />
Water Carrier started pumping water from the lake in 1964 and also influences the water<br />
level. In 1965, salt-water diversion canal was constructed to aid in reducing the high<br />
concentrations <strong>of</strong> sodium chloride in the lake. Before the construction <strong>of</strong> the canal,<br />
chloride concentration varied from 380-400 ppm Cl - . <strong>The</strong> operation <strong>of</strong> the canal and the<br />
heavy floods <strong>of</strong> 1968-69 caused a decline in the amount <strong>of</strong> salt in the Kinneret (stock<br />
and concentration) to an annual average (1988) <strong>of</strong> 208 ppm Cl - . Salinity, measured as<br />
Cl - concentration, at the start <strong>of</strong> this study (1996) was 218 ppm Cl - . <strong>The</strong> lake salinity<br />
has recently increased due to three consecutive drought years (1999- 2001) and a<br />
negative water budget during the summers. Because <strong>of</strong> the low water level, the saline<br />
springs are not being diverted through the canal and contribute about 5% to the<br />
increasing lake salinity.<br />
Laboratory experiments in this study showed adult E. <strong>drieschi</strong> reared in chloride<br />
concentrations >225 ppm (lake concentration during experimental period) had lower<br />
percent survival than those reared in
4.5.2 Temperature<br />
Temperature has both direct and indirect effects on zooplankton growth and<br />
development (Geiling & Campbell 1972, Herzig 1983, Edgar 1990,<br />
Ban 1992, 1994). An organisms’ behavior, development, reproduction, as well as the<br />
dynamics <strong>of</strong> an entire population may be directly influenced by changes in temperature.<br />
Zooplankton community responses to thermal dynamics are highly varied even among<br />
co-occurring species. Moore et al. (1996) reviewed effects <strong>of</strong> temperature on the<br />
population dynamics <strong>of</strong> freshwater zooplankton. <strong>The</strong>y observed that in many temperate<br />
lakes, survivorship declines at temperatures greater than 25 0 C. <strong>The</strong>y also observed that<br />
thermal responses are varied among co-occurring species and among cohorts as well.<br />
It appears that under sufficient food regimes, temperature is a major influence on<br />
stage development duration in E. <strong>drieschi</strong> in Lake Kinneret. It has become more<br />
apparent from the literature that differences exist in pre and post embryonic<br />
development times as well as inter-species stage duration from different bodies <strong>of</strong> water<br />
(Jacobs & Bouhuis 1979, Herzig 1983, Hart 1994, Calbet et al. 2000). Differences in<br />
development rates <strong>of</strong> the same species (E. gracilis) from different locations were<br />
suggested to be influenced mainly by temperature (Edgar 1990). <strong>The</strong>refore,<br />
measurements <strong>of</strong> a specific species may only be applicable to the water body in which it<br />
is found.<br />
Klein Breteler et al. (1994) examined the development time <strong>of</strong> five copepod species.<br />
He found the duration <strong>of</strong> the different life stages was not constant, but tended to increase<br />
slightly. <strong>The</strong> duration <strong>of</strong> the later copepodite stages was generally longer than the<br />
younger stages. This is compatible with the generalizations <strong>of</strong> Landry (1983) and with<br />
the results <strong>of</strong> this study. When discussing post-embryonic development <strong>of</strong> several<br />
species <strong>of</strong> <strong>Eudiaptomus</strong>, Jacobs (1979) noted differences in the development times <strong>of</strong><br />
the same species from different locations. Calbet et al. (2000) showed that at some<br />
specific sampling locations, juvenile and adult copepod growth rates were similar, while
at others, adult growth rates were higher. Comparison <strong>of</strong> pre-embryonic development<br />
times <strong>of</strong> tropical and sub-tropical diaptomids by Elmore (1983) showed differences in<br />
egg development most significant at high temperatures.<br />
Experiments showed development times and stage duration <strong>of</strong> E. <strong>drieschi</strong> at low<br />
temperatures were significantly different from the other treatments. Average<br />
development times at optimum temperatures, however, were seen to be comparable.<br />
Lake Kinneret rarely reaches an average temperature <strong>of</strong> 12 0 C in the epilimnion,<br />
therefore it is reasonable to assume that E. <strong>drieschi</strong> would not develop naturally at this<br />
temperature. <strong>The</strong> number <strong>of</strong> egg-bearing females begins to increase when the lake<br />
reaches 15 0 C, with maximum reproduction occurring at 18 -20 0 C. When the temperature<br />
rises above 22 0 C, the number <strong>of</strong> egg-bearing females decreases.<br />
<strong>The</strong> extremely high mortality seen in the lab at 24 0 C, and slow growth rates at 12 0 C<br />
is indicative <strong>of</strong> the thermal- sensitivity <strong>of</strong> E. <strong>drieschi</strong> in the Kinneret. Various authors<br />
have found that post-embryonic development rates are highly variable at higher<br />
temperatures (Huntly & Lopez 1992, Ban 1994). E. vulgaris (Schmeil 1896), a cold<br />
water species, experienced decreased rate <strong>of</strong> development at higher temperatures. This<br />
was attributed to thermal stress at temperatures not usually experienced in the wild<br />
(Kamps 1978).<br />
Indirectly, temperature could affect changes in the structure <strong>of</strong> the algae communities<br />
which provide food for the zooplankton. Rates <strong>of</strong> predation by zooplanktivorous fish are<br />
also influenced by temperature. Thus, investigating the appearance <strong>of</strong> a species in a<br />
previously unrecorded area where the temperature regime differs from its place <strong>of</strong> origin<br />
can be <strong>of</strong> significant interest and lead to understanding the evolutionary factors which<br />
govern species adaptations to new environments.
4.5.3 Food<br />
Calanoid copepods in general, are versatile feeders. <strong>The</strong>y are able to adapt to sudden<br />
changes in available particle size and abundance (Bogdan 1975, Burns 1994, Dumont<br />
1994, DeMott 1995). Food has been assumed to limit production in copepods by<br />
influencing growth and fecundity (Checkley 1980, Butler 1994). Changes in nutrient<br />
levels and community structure <strong>of</strong> phytoplankton assemblages, can result is variation in<br />
food quality and quantity. Although naupliar and copepodid stages need a reliable food<br />
source for natural development, it has been suggested that naupliar growth is less<br />
influenced by food supply (Hart 1990). Female reproduction and adult body size may<br />
also be influenced by food availability and quality.<br />
<strong>The</strong> phytoplankton population in lakes inhabited by <strong>Eudiaptomus</strong> species are<br />
comprised <strong>of</strong> Chlamydomonas and Rhodomonas species, among others (Beeton 1981,<br />
Zankai 1991, Santer 1994), and these genera are present in the Kinneret as well.<br />
Although experiments carried out in this study showed that E. <strong>drieschi</strong> does poorly in<br />
food concentrations less than 7,000 cells ml -1 , nanoplankton concentrations do not drop<br />
below 9.8 x 10 3 cells ml –1 in the Kinneret, suggesting that E. <strong>drieschi</strong> is not food limited<br />
in the Kinneret.
5. Conclusions. <strong>The</strong> Salinity Filter in an Old Lake.<br />
Lake Kinneret is among the early Pleistocene ancient lakes <strong>of</strong> the world. It is<br />
characterized by higher species diversity in the littoral and benthos that is in contrast to<br />
a simpler less diversified pelagic community structure. <strong>The</strong> open water is considered too<br />
homogeneous an environment to allow a high species diversity. Also the number <strong>of</strong><br />
endemic species is relatively small in the Kinneret in comparison to other pre-glacial<br />
lakes. Tchernov (1975) indicates that the small number <strong>of</strong> species found today in the<br />
Kinneret , may be a result <strong>of</strong> geological events that occurred during the Pleistocene<br />
along the Jordan Rift Valley, however Por (1963) attributes it to the oligohaline nature<br />
<strong>of</strong> the lake. A number <strong>of</strong> marine relict species among the lake fauna may be explained as<br />
survivors <strong>of</strong> the receding Pliocene Mediterranean. Representitives <strong>of</strong> the Mollusca and<br />
Harpacticoida, are found to be related to species from the Anatolian lacustrine basin<br />
(Lake Egerdir, Turkey), which suggests a “natural link” for species distribution (Por<br />
1963).<br />
Over the years, there has been no continous survey <strong>of</strong> the species biodiversity <strong>of</strong><br />
the lake. According to Komarovsky (1959), no changes had occurred “in the<br />
composition <strong>of</strong> the plankton during a period <strong>of</strong> over sixty years”. Komarovsky himself<br />
reported on the presence <strong>of</strong> a single female specimen Moina rectirostris in material<br />
collected from 1948-49 which had not been found by other investigators and was<br />
considered “accidental”. Bromley (1993) has identified 4 species <strong>of</strong> Moina in Israel, <strong>of</strong><br />
which Moina micrura dubia (Richard) is now recognized as a regular constituent <strong>of</strong> the<br />
Lake Kinneret cladocera. Daphnia lumholtzi (Sars),was recorded in the lake in the years<br />
prior to and including 1956. D. lumholtzi was previously known from African Rift<br />
valley lakes (Lake Albert) with high salanities. Throughout the period (prior to the<br />
1950’s) that D. lumholtzi was found in the Kinnerert, average salinity was >300 ppm
chloride. Between 1955-69, salinity varied from 350 ppm, to 250 ppm Cl - . Gophen<br />
examined material collected in 1958-1960 and did not find D. lumholtzi . Subsequent<br />
studies (Por 1968, Gophen 1978) were also unsuccessful. <strong>The</strong>r dissappearence <strong>of</strong> D.<br />
lumholtzi and the incorporation <strong>of</strong> M. micrura dubia to the Kinneret plankton, are<br />
indications <strong>of</strong> the changes undergone by the system.<br />
Despite the slightly oligohaline nature <strong>of</strong> the lake, the Kinneret, overall, has<br />
almost no seasonal fluctuations <strong>of</strong> salinity. However, the Kinneret system has undergone<br />
a series <strong>of</strong> temporal modifications, some man-made and some natural, which have<br />
resulted in alterations in its biological regime. <strong>The</strong>se changes may have contributed to a<br />
temporary variation in the “biological filter barrier” and creating an environment<br />
suitable for <strong>Eudiaptomus</strong> <strong>drieschi</strong> to successfully establish itself as a new member <strong>of</strong> the<br />
pelagic fauna <strong>of</strong> Lake Kinneret.<br />
<strong>The</strong> fact that an organism reaches the lake does not necessarily ensure its<br />
incorporation into the lake ecosystem (Williamson 1996). It would require the<br />
breakdown or alteration <strong>of</strong> the natural “fauna filters” i.e.: salinity, temperature, ionic<br />
composition in the system to allow an organism to “invade”.<br />
Since an invading organism is defined as one that is found anywhere outside its<br />
previous range (Williamson 1996), E. <strong>drieschi</strong> may be seen to have successfully invaded<br />
the Kinneret open water system during the period when chloride concentrations were<br />
low. It adapted to the extreme conditions by increasing production <strong>of</strong> resting eggs as the<br />
lake temperature increased. This is the first record <strong>of</strong> E. <strong>drieschi</strong> in Israel, as well as the<br />
first report <strong>of</strong> a diaptomid species becoming established in Lake Kinneret. Previous<br />
reports <strong>of</strong> the diaptomid E. gracilis in the lake may be the result <strong>of</strong> erroneous<br />
identification.
E. <strong>drieschi</strong> has not been recorded from the Hula Reserve, from the waters <strong>of</strong> the<br />
partially re-flooded Hula Lake (Lake Agmon), (Por, pers. comm.), nor has it been found<br />
in any other water body in Israel where diaptomid species are present. <strong>The</strong> relatively<br />
young age <strong>of</strong> the Kinneret bottom sediments (Nishri et al 1998) in which resting eggs<br />
are found, indicate the recent invasion <strong>of</strong> this organism to the pelagic waters <strong>of</strong> the lake<br />
(early to mid 1980’s).<br />
A potential vector for resting egg transport via the gut contents <strong>of</strong> fish is likely,<br />
as the resting eggs have no spines or hooks on the outer surface when examined with a<br />
scanning electron microscope. This would tend to rule out passive transport by air, as a<br />
means <strong>of</strong> dispersion. Viable resting eggs were found in the gut <strong>of</strong> larval catfish (Clarias<br />
gariepinus) from the lake. It is conceivable that E. <strong>drieschi</strong> may have been introduced<br />
into the lake by migrating, piscivorous birds from Turkey or Cyprus.<br />
Although found throughout the year in other locations, e.g.: Lake Skadar<br />
(Scutari) in Montenegro (Petkovic 1981) and Lake Poyraz and L. Egerdir, Anatolia<br />
(Gunguz 1998), it disappears from the water colum in the Kinneret during the summer<br />
and early fall. E. <strong>drieschi</strong> appears to have adapted to the environment fo Lake Kinnerert<br />
by evolving a life history which removres it from the water column during periods <strong>of</strong><br />
high temperature. This is the first mention <strong>of</strong> resting eggs in the copepod fauna <strong>of</strong> Lake<br />
Kinneret.<br />
Salinity, (chloride concentration) decreased from 400 ppm in the late 1960’s to<br />
208 ppm in the late 1980’s. This reduction <strong>of</strong> salinity concentration is considered to be<br />
the primary releasing factor in the establishment <strong>of</strong> E. <strong>drieschi</strong> throughout the lake.<br />
Salinity has begun to increase recently due to successive drought years, ans is currently<br />
(2001) 380 ppm Cl - . E. <strong>drieschi</strong> is presently not encountered in the Lake.
This study <strong>of</strong>fered the rare (and fortuitous) opportunity to witness a temporary<br />
change in the animal realm <strong>of</strong> Lake Kinneret, induced by changes in the salinity regime.<br />
Laboratory studies confirmed the sensitivity and negative response <strong>of</strong> E. <strong>drieschi</strong> to<br />
abrupt changes in salinity concentrations.<br />
<strong>The</strong> very restricted seasonal pattern <strong>of</strong> E. <strong>drieschi</strong> in the lake provides a<br />
sensitive indicator for future changes in the temperature regime <strong>of</strong> the Lake. <strong>The</strong><br />
temperature sensitivity <strong>of</strong> E. <strong>drieschi</strong> may serve as a yardstick for overall global<br />
warming-by signaling warming <strong>of</strong> Lake Kinneret.
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Proceedings <strong>of</strong> the 7 th International Conference on Copepoda<br />
Curitiba, Brazil<br />
25-31 July, 1999<br />
<strong>The</strong> occurrence <strong>of</strong> the diaptomid <strong>Eudiaptomus</strong> <strong>drieschi</strong> (<strong>Poppe</strong> and <strong>Mrazek</strong> <strong>1895</strong>) in<br />
Lake Kinneret, Israel.<br />
B. Azoulay, M. Gophen, F.D. Por<br />
Prior to the mid-eighties, diaptomid copepods were not found in the routine samples <strong>of</strong><br />
the pelagic waters <strong>of</strong> Lake Kinneret. Early surveys reported sporadic appearances <strong>of</strong><br />
diaptomids in the lake, especially after winter floods. After 1986, the consistent presence<br />
<strong>of</strong> the diaptomid <strong>Eudiaptomus</strong> <strong>drieschi</strong> (<strong>Poppe</strong> and <strong>Mrazek</strong> <strong>1895</strong>), in the <strong>of</strong>fshore zone<br />
(pelagic) <strong>of</strong> Lake Kinneret was recorded. Population densities and life stage distribution<br />
<strong>of</strong> copepods have been monitored in the lake since 1996. A strong seasonal periodicity<br />
was indicated with the highest densities in winter / spring and very low in the summer.<br />
Two, 24-hour surveys were conducted during those periods. It was observed that during<br />
the April study (spring) juvenile copepods had a strong association with nanoplankton.<br />
<strong>The</strong> high summer temperatures are apparently one <strong>of</strong> the pressures that drive E. <strong>drieschi</strong><br />
in Lake Kinneret to produce a resting egg. Viable eggs have been extracted from<br />
sediment cores up to a depth <strong>of</strong> 10 cm. Experiments examining temperature and salinity<br />
tolerances were conducted in the lab as well as body length measurements <strong>of</strong> each life<br />
stage. Adult E. <strong>drieschi</strong> do not appear to reproduce in high salinities, and are sensitive to<br />
high temperatures (>22 0 C).
האאוטאקולוגיה של<br />
(<strong>Poppe</strong> and <strong>Mrazek</strong> <strong>1895</strong>) <strong>Eudiaptomus</strong> <strong>drieschi</strong><br />
(קופפודה, קלנואידה) בכנרת.<br />
חיבור מאת: בוני ר. אזולאי<br />
מדרכים אקדמאים:<br />
פרופ. משה גפן<br />
פרופ. פ. דב פור<br />
הוגש לסינט האוניברסיטה העברית, ירושלים<br />
2002 יולי,
מ-<br />
תקציר<br />
עד אמצע שנות השמונים, דיאפטומידים (קופפודה, קלנואידה) היו רק "אורחים מזדמנים"<br />
בכנרת.<br />
במחקרים קודמים דווח על מציאות דלה מפוזרת מאוד בזמן של דיאפטומידים רק באיזור<br />
הליאוראל של הכנרת, במיוחד לאחר שטפונות חורפיים חזקים.<br />
בדגימות שנאספו אחרי 1986<br />
אובחנה נוכחות מתמשכת של אאודיאפטומוס דריישי (<strong>Poppe</strong> & <strong>Mrazek</strong> (<strong>1895</strong> <strong>Eudiaptomus</strong> <strong>drieschi</strong><br />
באיזור הפלגיאל של האגם.<br />
זה הדיווח הראשון ברקורד הזואופלנקטון של הכנרת על תוצאה נרחבת<br />
של א. דריישי באגם, ודווח ראשון על חדירה כל כך נרחבת שלו אל הכנרת.<br />
דווחה בעבר מסרי-לנקה, יוגוסלביה, יון ותורכיה.<br />
מציאותו של א. דריישי<br />
מעקב רצוף ספירה וחקר אוכלוסיתו החלו<br />
ב1994-.<br />
ריכוז האורגניזמים במי האגם, לפי הדרגות במחזור החיים שלו נמדדים בתחנה קבועה<br />
תחנה F<br />
(עומק 20 מ').<br />
שבצפון-מערב הכנרת החל משנת 1996.<br />
לא אובחנו דורות קוהרנטים בתוך אוכלוסיות של א. דריישי בכנרת.<br />
האוכלוסיות שלו<br />
בכנרת מראות על הרכב רב-גילי ורבייה רצופה בעונות בהן הוא נפוץ.<br />
כדי להעריך את הדינמיקה של<br />
הרבייה שלו נמדדו באופן נסיוני במעבדה הביומסה, קצב גידול וזמן ההתפתחות של כל שלב במחזור<br />
חייו. פרטים גודלו בטמפרטורות שונות ובדרגות מליחות שונות של מי אגם.<br />
זמן ההתפתחות של כל<br />
שלב ותוספת הגידול נמדדו ברציפות.<br />
מאז 1969 התרחשו במערכת הכנרת מספר שינויים: עלה מגוון המינים של הזואופלנקטון<br />
באפילימניון של הכנרת ע"י הופעה של מינים חדשים: כידורוס ספריקוס<br />
(Leydig) (Moina retrorostris) מוינה רקטירוסטריס ; ( By Birge) (Chydorus sphaericus)<br />
קונוכלילואידס sp.) (Conochiloides ; אנוריאופסיס פייזה fissa) (Gosse)(Anuraeopsis<br />
אובחנו גם שינויים בפיטופלנקטון (בעיקר ירוקיות, כחוליות ולהוביות), המליחות ירדה מ400<br />
"ג<br />
כלוריד לליטר<br />
(מגכ"ל) בשנות השישים עד ל208 מגכ"ל בשנות ה80-.<br />
נמצא שהירידה במליחות היא כנראה הגורם הראשוני לפלישה של א. דריישי לפלגיאל של הכנרת.<br />
לאחרונה עלתה המליחות שוב עד ל283- מגכ"ל וכיום נעלמו לכן אוכלוסיות ה א. דריישי.<br />
ריכוזי א. דריישי בכנרת מראים על שינויים עונתיים: ריכוזים גבוהים בחורף-אביב ונמוכים מאוד<br />
בקיץ-סתיו.<br />
מיני דיאפטומידים רבים מייצרים שני טיפוסי ביצים: 1) ביצים סוביטאניות כאלו שמתבקעות מיד,<br />
2) ביצי קיימא-בנטיות שמוטלות, שוקעות לתוך הסדימנטים ומתבקעות מאוחר יותר.<br />
אוכלוסיות<br />
א. דריישי בכנרת מתחדשות כל שנה בחורף לאחר ה"היפוך", מתוך "בנק" ביצי קיימא שבסדימנטים
והוטלו שנה קודם לכך בתקופה בה טמפ' המים עלתה אל מעל הטולרס הטרמי שלהם (גבול<br />
הסבילות הטרמי), שהוא מעל . 22 0 C<br />
ביצי קיימא שנאספו מהסדימנטים בכנרת אינן שונות באופן<br />
מורפולוגי מהביצים הסוביטאניות, כפי שנבדק במיקרוסקופ אלקטרוני.<br />
במיקרוסקופ אור רגיל,<br />
ולאחר ששומרו ונצבעו בלוגול (1990 (Lohner ניתן להבדיל ביניהן.<br />
צילומים במיקרוסקופ אלקטרוני<br />
סורק הראו ששטח הפנים של ביצי קיימא הוא חלק, וללא קוצים או סטרקטורות בולטות אחרות.<br />
עובדה זו מרמזת על אפשרות שתפוצתן יכולה להעשות ע"י דגים.<br />
נמצאו ביצי קיימא במערכת<br />
העיכול של דגיגי שפמנון בכנרת.<br />
יתכן ש א. דריישי הגיע לכנרת ע"י צפרים נודדות טורפות דגים<br />
והופץ באגם ע"י דגים בנטיבוריים.<br />
פלישה של אורגניזמים אקוסטיים לתוך אקוסיסטמה שלא היו בה מקודם היא מדד לשינויים<br />
שעוברת המערכת (הרבה פעמים מעשה ידי-אדם) המאפשרים לאורגניזם הפולש להתבסס בה.<br />
אורגניזם פולש מוגדר ככזה לאחר שנצפתה תפוצה שלו שונה מתחום התפשטותו בעבר.<br />
הצלחת<br />
הפלישה היא בד"כ מועטה. א. דריישי הצליח לפלוש לאפילימניון של הכנרת ע"י כך שתפש חלקית<br />
מקומם של אחרים בתוך נישה אקולוגית זו שהיתה תפוסה כולה בעבר והסתגל לטמפרטורות<br />
הקיצוניות ע"י יצירת ביצי קיימא.
עבודה זו נעשתה בהדרכתם של:<br />
פרופ. פ. דב פור,<br />
מחלקת אבולוציה ,ססטמטיקה, ואקולוגיה<br />
האוניברסיטה העברית, ירושלים.<br />
פרופ. משה גפן,<br />
המעבדה לחקר הכנרת ע'ש יגאל אלון,<br />
חקר ימים ואגמים לישראל, בע'מ.
האאוטאקולוגיה של (<strong>Poppe</strong> and <strong>Mrazek</strong> <strong>1895</strong>) <strong>Eudiaptomus</strong> <strong>drieschi</strong><br />
(קופפודה, קלנואידה) בכנרת.<br />
חיבור לשם קבלת התואר "דוקטור לפילוסופיה"<br />
מאת בוני רשל אזולאי<br />
הוגש לסינט האוניברסיטה העברית, ירושלים<br />
2002 יוני