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$Wetenschap - \Nijverheid- Handel$

SEASONAL VARIATION IN BODY WEIGHT OF BIVALVES Table 9. Correlations between ho.lv condiiion ol loui bivalve Species tea vv.iiei temperature and chlorophyll a concenliations: same data as given in lig. 9, All corrcialions are highly significant (p < 0.00! i; n is given between brackets. Scrobicularia Mya Cerasti temperature tMorophyUa Muci min 059(78) 0.74 1901 0.69(66) 0.48(91) fi wbicularia 0.59 (78) 0.56(54) 0.59(79| 039(59) Mya 0.65(65) 0.48(91) Cerastoderma 0.54 (67) 032(50) temperature 0.44(70) This figure also shows the concentration of chlorophyll a in the surface water in the gullies -a measure of the available food supply- and monthly mean sea water temperatures. With all data pooled, significantly positive correlations between the bodv weight of the four species and both sea water temperatures and chlorophyll a concentrations were found (Table 9). Weight variation in winter Body weights were low in mild winters but remained relatively high when winter temperatures were low (Fig. 9). To investigate this further, a selection was made of measurements of body weights taken during adjacent months in the period November to February. The changes in body weight, relative to the preceding month, appeared to be independent of food supply, but higher sea water temperature had a significant negative effect on body weight in three of the four species dig. 10). The slopes did not change when food supply was entered into the multiple regressions. The relationships shown in Fig. 10, suggest that winter is a starving period during which the decrease of body weight depends on the temperature-related cost oi living. Weight variation and gametogenesis Seasonal variations in body weight during summer have been attributed to the development and spawning of gametes (e.g. Hughes 1970b). The contribution of gonads to total body weight can be estimated from the individual weights of animals at different reproductive stages. Figure 11 shows that Scrobicularia 35 mm long with few or no gametes -either before the Start of the gametogenesis or after spawning- weighed about 200 mg. whereas individuals with gametes had a body 38 weight of about 250 mg- On this basis the increment in body mass due to seasonal development of the gonads works out at about 20%. similar to the figure mentioned earlier for Macoma. However, the presence nl gametes did not explain the whole variation in body weight between May and August. There was still a significant seasonal variation in body weight for specimens with equal gamete scores. Thus the decrease of body weighi alter June appears to have been independent of the development or loss of the gametes The effects of season and gamete development were similar over two years (Fig. 11). Nonetheless, there was a remarkable difference between the summers of 1981 and 1982 (Fig. 9). The relatively high body weight in 1981 can be attributed to gametogenesis. In June and July 1981, 98% of the individuals reached gamete stage 3 or 4. whereas in 1982 this was only true for 45%. In conclusion, reproductive tissue explains only a part of the enhanced summer weight of Scrobicularia, whereas the differences between summers can be attributed to the variation in the amount of gametes produced. Discussion Weight change, growth and spawning The body weight in Macoma in the Wadden Sea is at lis highest in May and June (Beukema & de Bruin 1977, Beukema et al. 1985. Beukema & Desprez 1986. this paper: Figs. 5, 8, 9) and Cerastoderma, Scrobicularia and Mya reach maximum condition in the same months (Figs. 7. 8). In NW. Europe, this is
20 10 0 -10 -20h 2 3 4 5 6 7 8 9 sea temperature (°C) SEASONAL VARIATION IN BODY WEIGHT OF BIVALVES M. balihica r=-0 23 p. 0 28 n. 23 Fig. 10. Relative monthly changes m AFDW I'i I as a Innelion ol Ihe average sea waler tcinperalurc during that same month in Hop io boOom) Macoma (15 mini. Scrobicularia 135 mnn, Mya (30 mm) I 'mi (20 mm). These data are also given in Fig. 9 and refer to the winter period (November-February). 10 39 the period during which shell growth is also greatest in Macoma (Beukema & de Bruin 1977, Beukema ei al. 19X5. Beukema & Desprez 1986, Desprez etal. 1986), in Scrobicularia (Wanink & Zwarts unpubl.). Mya uk & Bos 1985) and Cerastoderma (Kristensen 1957. Hancock ct Franklin 1972. Ankar 19X0. Fssink & Bos 1985. Desprez et al. I98n). All species thus appear to be ill a good condition during the main growing season. Indeed, in a comparison between years, length increment and body weight at (he em\ of the growing season in Macoma were found to be closely Correlated (Beukema ei al. 1985). The weight of the gametes relative to the total l>. id} weight in Macoma was estimated at 24'. in the laboraton (de Wilde & Berghuis |97Si. at 15 and WM in the field in different years in the same place (Beukema et al. 1985) and at 7 and 27 f 3/4 of Ihe digestive gland was covered hv gonad lissucs. while II and III are intermediate classes. IVI reiers to individuals after spawning The results of two-Way analyses of variance arc given: the effect of the factors (month and gonad) is highly -iimilicant. as well as the interaction between both fact.
Page 1 and 2: WADERS AND THEIR ESTUARINE FOOD SUP
Page 3 and 4: plia^ohi. WADERS AND THEIR ESTUARI
Page 5 and 6: Waders and their estuarine food sup
Page 7 and 8: WADERS AND THEIR ESTUARINE FOOD SUP
Page 10 and 11: figuren: Dick Visser omslagfoto: Ja
Page 12 and 13: 15 Versatility of male curlews (Num
Page 15 and 16: That science is making progress, ma
Page 17 and 18: INTRODUCTION The remnants of brushw
Page 19 and 20: When hcnlhic bivalves extend llien
Page 21 and 22: the burrow depths and on the fracti
Page 23 and 24: INTRODUCTION Ms,i invest 409 of (he
Page 25 and 26: able lo sw itch 10 oiher prey which
Page 27 and 28: Long-term, broadly-based research c
Page 29 and 30: Chapter 1 SEASONAL VARIATION IN BOD
Page 31 and 32: SEASONAL VARIATION IN BODY WEIGHT O
Page 33 and 34: Tahle 1 Weight loss ('•- ± SE) m
Page 39 and 40: i 60 50 40 30 20 10 0 • INFESTED
Page 41: 240- SEASONAL VARIATION IN BODY WEI
Page 45 and 46: a E 400 - S. plana 35 mm 320 240 16
Page 49 and 50: Chapter 2 HOW THE FOOD SUPPLY HARVE
Page 51 and 52: FOOD SUPPLY HARVESTABLE BY WADERS H
Page 53 and 54: Methods The study sites were situat
Page 55 and 56: less than that of bivalves, partly
Page 57 and 58: I Fig. 3). Peak condition was reach
Page 59 and 60: total biomass since most of those t
Page 61 and 62: on the basis of the preceding and t
Page 63 and 64: However, for obvious reasons, we ma
Page 65 and 66: prey. A decrease in the prey densit
Page 67 and 68: Tahle 2. The intake rate ol < lyste
Page 69 and 70: * ' % -. . ; a X - . - * • ^ •
Page 71 and 72: (Zwarts & Wanink 1989). In quiet we
Page 73 and 74: general law relating handling time
Page 75 and 76: nearly twice as much time (0.79 s).
Page 77 and 78: 4 5 6 7 8 9 size class of Corophium
Page 79 and 80: and annually. Second, the lower siz
Page 81 and 82: Prey switching Waders feeding on ti
Page 83 and 84: autumn and spring, and the contrary
Page 85 and 86: where they switch to surface-living
Page 87 and 88: Chapter 3 BURYING DEPTH OF THE BENT
Page 89 and 90: DEPTH AND SIPHON CROPPING IN SCROBI
Page 91 and 92: I DEPTH AND SIPHON CROPPING IN SCRO
Page 93 and 94:
DEPTH AND SIPHON CROPPING IN SCROBI
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Table 3. Three-Way analysis Of vari
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Chapter 4 SIPHON SIZE AND BURYING D
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15 20 size (mm) Fig. 3. Cerasioderm
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10 size (mm) SIPHON SIZE AND DEPTH
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o, 7 01 5 | * CL 5- SIPHON SIZE AND
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4 Q) Si •a a. 16- 20- A predator:
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prey risk for an animal al a depth
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Table 6. Size al which there is a m
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* ' 1 /-/ "».-^*«C
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face and so expose themselves to a
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surface in die containers was varie
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50 OOF 310.00 I 5.00 ^ 1.00 3=" 0.5
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Tahle 1. Macoma and Scrobicularia.
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siphon would not have to reach the
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known siphon weight and burying dep
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ACCESSIBLE PREY ARE OFTEN IN POOR C
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1 2 3 4 burying depth (cm) Kin. I.
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I—1 • • : : : : ! - ! -|-r 0
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Chapter 7 DOES AN OPTIMALLY FORAGIN
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OPTIMAL FORAGING AND THE FUNCTIONAL
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100 200 300 prey density (n-m-2) Fi
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Table I. Results of five one way an
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Table 2. Results of eight iwo-wav a
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prey density II III Fig. 12. Freque
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PREY SIZE SELECTION AND INTAKE RATE
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Predicted 'passive size selection'
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lig. 2. Larger Mussels are less ava
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Fig. 5. Scrobicularia plana. Size c
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and maiiv are too thick-shelled to
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The measurements of handling time i
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1 2 3 4 5 6 7 probing depth (cm PRE
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valves may vary by a factor of two
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optimal foraging model, the minimum
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their gut is full? Do they reduce t
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PREY PROFITABILITY AND INTAKE RATE
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catchers to take only certain prey
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licult error of estimate arose if p
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Counts of feeding and non-feeding b
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20 30 40 50 shell length (mm) PREY
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Nereis Arenicola tipuia earthwo'm M
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take rate. We might therefore expec
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prey species, using parallel slopes
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5.0 4.0 1-3.0 a & • % * • * •
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time during the feeding period. As
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winter. Similarly, handling time in
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5.0 - f-4.0 S 3.0 in I 20 a 2 a | 1
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situation arrived in the western pa
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• ' • 14 PREY PROFITABILITY AND
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Notes lo appendix: PREY PROFITABILI
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Chapter 10 WHY OYSTERCATCHERS HAEMA
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2 4 6 8 10 time on feeding area (h)
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80- 60- o 80 60- 40- 20- INTAKE RAT
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est of bod\ behind: an estimated 22
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INTAKE RATE AND PROCESSING RATE IN
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Wanink 1993). The energy content of
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(7) Age All studies dealt with adul
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irds over long periods. As an examp
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Discussion There is no difference i
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comparison between the weight of ih
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. 1', L ! •
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Introduction PREDICTING SEASONAL AN
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PREDICTING SEASONAL AND ANNUAL FLUC
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1000 r 1 II" 1 - r^Jan'80 PREDICTIN
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IOO BO 60 40 20 0 PREDICTING SEASON
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WHY KNOT TAKE MEDIUM-SIZED MACOMA W
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in Zwarts & Esselink 1989). The len
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shell length (mm) FIR. 3. Peringia.
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fused, specimens larger than this w
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50 100- s s I — f = S. plana, n=2
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area is twice as large as the touch
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10 15 lower size threshold (mm) Fig
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lime (Hughes 1979). This would furt
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WHY KNOT TAKE MEDIUM-SIZED MACOMA T
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Chapter 13 ANNUAL AND SEASONAL VARI
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VARIATION IN FOOD SUPPLY OF KNOT AN
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Two sites (N and M in Fig. 2) were
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20 30 VARIATION IN FOOD SUPPLY OF K
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20 l i r'l ' i •o j^y^T n ^ ' " ^
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July ' Aug ' Sept Fig. 9. Proportio
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available. There must, however, be
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Chapter 14 SEASONAL TREND IN BURROW
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BURROWING AND FEEDING IN NEREIS SEA
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Table 2. Results of a 2-way analysi
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June 1981 June 1982 is * N.MUD •
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8 10 I 12 JZ 5. -g 1*» •e o i 16
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6 - n=!080 5 • g 4 CP > i 3 CO CD
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1985) and Curlew (/wails ,v, Lsseli
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Chapter 15 VERSATILITY OF MALE CURL
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Smid! 1951. Muus 1967, Wolff 1973,
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0.6 0.8 1.0 1.2 1.4 1.6 jaw lengih
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Na oi both Nrieck Fig. 7. Numenius
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6 8 10 12 14 16 18 worm length (cm)
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too (Fig. 11 A). Indeed, the averag
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VERSATILITY OF CURLEWS FEEDING ON N
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total time spent al the surface. Th
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2 4 . • 2.2 • 30 .-.2.0 to Q. 1
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PREY DEPLETION BY OYSTERCATCHER AND
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the rule: the observed lower limit
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to locate the clams after they had
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Curlew, by bury ing some hundreds o
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PREY DEPLETION BY OYSTERCATCHER AND
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SAMENVATTING 345
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Voorgeschiedenis In 1960 verscheen
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maken. Als gebied A een grotere voe
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omdat ze nog vrijwel niets wegen. l
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kunnen opzuigen. of diep leven en z
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van de uitgerekte sifo over het wad
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het toen niet gemakkelijk hebben ge
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doende nonnetjes van 10 tot 15 mm l
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aangevoerde voedsel en de wulp past
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zijn dan twee jaar en wulpen geen s
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was dan ook dank/ij de inzet van al
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REFERENCES 367
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Allen RL. 1983. Feeding behaviour o
Page 367 and 368:
BreyT. 1989. Der Einfluss physikali
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latie tol chironoiiiiilen en de wai
Page 371 and 372:
huch der Vogel Milteleuropas, Band
Page 373 and 374:
llolmann II. & H. Huerschelmann 196
Page 375 and 376:
l-cndrem D.W. 1984. Flocking, feedi
Page 377 and 378:
Pekkarinen M. 1984. Regeneration of
Page 379 and 380:
lion of Mussels Mytilus edulis hy O
Page 381 and 382:
lulal Dal esiuanes: a comparison of
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