The ecology of eelgrass meadows in the Pacific Northwest: A ...

More documents

Recommendations

Info

leaves overtopped them and created deeper shade. In the subtidal zone sexual reproduction does not play an important role in the growth and maintenance of an eelgrass meadow (Phillips 1972; Kentula 1983). During a study in Puget Sound, Phillips (1972) tagged numerous seedlings in the subtidal and found 100% mortality. In one denuding experiment only one seedling colonized a 1-m2 plot in the subtidal, while five seedlings appeared in an intertidal plot. There appears to be a direct relationship between the amount of physical disturbance (high or low water temperatures, intertidal conditions) and a dependence on sexual reprduction (dqree of flower and seed production and survival of seedlings) to maintain an eelgrass meadow in the intertidal zone. In the subtidal zone there is a dependence on vegetative growth to maintain the meadow s hilli ips 1972; Phillips et al. 1983b). 2.3 PHYSI0IXX;ICAL REQUI~S AND FUNCTIONS Table 6 includes a general list of habitat factors under which eelyrass grows (phillips 1974). Temperature Eelgrass worldwide survives under a wide range of water temperatures. It appears that an overall range of 5O C to 27O C (41° F to 80.5O F) would include most areas where the plant is established. Extreme limits at which eelgrass is known to survive are a minimum of -6O C (21.2O F) in Alaska (Biebl and McRoy 1971) and a maximum of 40.5' C (104.9' F) (Arasaki 1950) measured at a substrate depth of 3-5 cm. qptirnm temperatures for growth seem to lie between l@ C and 200 C (5a0 F to 68O F) in most areas of the world hilli ips 1974). In Puget Sound vegetative and reproductive activity occurs in a temperature range of 6.0O C to 12.5O C (42.8O F to 54.5O F). In local areas water temperatures may warm to 18O C (64.4O F) during daytime summer low tides. In the Gulf of California, Mexico, eelgrass decays when the water temperature exceeds 27O C (~0.5~ F). In Netarts Bay, Oregon, water temperature varies from 8O C to 11° C (46.4O F to 51.8O F) in winter to ~ 6 . 0 C ~ to 28.5O C (60.8O F to 83.3O F) in summer (Stout 1976). The latter temperature was rare and only occurred over a tideflat during daytime summer low tides. All seagrass species appear to have upper/ lower temperature tolerance levels (Thayer et al. 1975a; McMillan 1978). McMillan (1978) subjected three different Puget Sound eelgrass populations, each with different leaf widths, to three temperature treatments. After 4 mo. each population continued to maintain its original distinct genetic limits of ecoplasticity to their environment. These tolerance levels vary with the local area (~c~illan 1979; Phillips et a1 1983a). Eelgrass at the northern and southern extremes of distribution on both the Atlantic and Pacific coasts appears to tolerate a much broader temperature range than eelgrass in the middle of the ranye (Phillips 1980). The relationship of water temperature to eelgrass reproductive @ysiology was shown by Phillips et al. (1983a). Analyzing collections from a wide distributional range on both coastlines in North America, they demonstrated a significant correlation of plant activity with water temperature. It was also suggested that eelgrass may form genotypes with different temperature requirements that are selectively adapted to conditions at local sites and over a latitudinal gradient. Biebl and ~cRoy(1971) demonstrated that eelgrass in Izembek Lagoon possessed a broad response to temperature. Local plants survived freezing in ice at -6O C (21.1° F) , but eelgrass from Washington State and California could not. Tidepool eelgrass in Izembek Lagoon showed increased photosynthesis and survival up to 35O C (95O F), while photosynthesis and survival in subtidal plants declined above 30O C (86O F). Short (1975) diagrammed a relationship of eelgrass productivity and water 13
Table 6. Numerical characteristics of eelgrass habitat factors (Phillips 1974). Habitat factor Vegetative growth Flcwering state Seed gemination Temperature optinam lo0 C to 20" C 15O-20O C (a0 C-go C in Puget sound) 5O-10O C (41.0° F- (50.0" F to 68.0° F) (59°Fto680F;46.40Fto48.20~) 50-00F) Salinity Optimm Depth Light Freshwater - 42 ppt -- 10-30 ppt %me as optimum 1.8 m above M U to 30 m deep -- 4.5-9.1 ppt -- MLLW - 6.6 m belw MLLW (11 rn at high tide) Effect unkmwn LJo effect Substrate Range Pure firm sand to plre soft ~md Mix& sand and mud 7.3-9.0 No effect Effect unkm No effect Effect u r ~ k m ~ Water Wtion w e Waves to stagnant water -- opt imm Little wave action. Gentle currents to 3.5 kmts Effect l.dcrmm -- Effect unkmm temperature (after BiebL and McRoy 1971; (~stenfeld 1908). In the Baltic Sea Figure 6). salinities are seasonally diluted to 6 ppt. At this time eelgrass becomes Salinity stunted (Kikuchi and Peres 1977). Eelgrass is an euryhaline species a able 6). It grows at stream mouths when the water is fresh at low tide (~sterhout 1917; Phillips unpublished research, Hood Canal, Washington) but does not grow in persistent fresh water. Tutin (1938) found eelgrass at Chesil Beach, Borest, England, where summer water salinity was as high as 42 ppt. In Puget Sound eelgrass grows best in a salinity range of 20 ppt-32 Ppt. A salinity range of 10 ppt-30 ppt is optimum for growth In Alaska eelgrass maintained an osmotic resistance to salinity changes from freshwater to 93 ppt (~iebl and McRoy 1971). In 124 ppt leaves were killed. Positive net production was found in a range from freshwater to 56 ppt, with a maximum in 31 ppt (normal seawater). Respiration was depressed in freshwater but was only slightly affected from 31 ppt to 93 ppt. Tide pool and subtidal plants showed the same reactions. Leaves of both populations were pretreated by soaking in
Page 2 and 3: ~~~/0~-84/24 September 1984 THE ECO
Page 4 and 5: PREFACE Nearly half the population
Page 6 and 7: CONTENTS PREFACE ..................
Page 8 and 9: FIGURES Number 1 2 ................
Page 10 and 11: ACKNOWLEDGMENTS I wish to acknowled
Page 12 and 13: Because eelgrass is a rooted plant,
Page 14 and 15: CHAPTER 1 THE PHYSIOGRAPHIC SETTING
Page 16 and 17: Table 1. Precipitation, temperature
Page 18 and 19: Table 2. Distribution and extent of
Page 20 and 21: Table 2. (Concluded) Extent of mat
Page 22 and 23: CHAPTER 2 THE BIOLOGY OF EELGRASS 2
Page 24 and 25: Table 4. Field observations on eelg
Page 28 and 29: 1.0- influence the redox potential
Page 30 and 31: Oxygen There are Little data to ind
Page 32 and 33: enough, increased erosion of bottom
Page 34 and 35: The terms used to describe biomass
Page 36 and 37: estimates are reported on work done
Page 38 and 39: Figure 10. Eelgrass at Blakely Isla
Page 40 and 41: increase in p~), and the sediments
Page 42 and 43: particulate matter and DOM were hig
Page 44 and 45: Table 9. Nutrient content of eelgra
Page 46 and 47: ecause it is dominated by a single
Page 48 and 49: epibenthos, and other components al
Page 50 and 51: shorebirds). From a recent thorough
Page 52 and 53: pink shrimp, and bottom fish (Proct
Page 54 and 55: Table 13 a. (Continued) Phyltnn, cl
Page 56 and 57: Phylum, class, and Resident or Livi
Page 58 and 59: Table 13b. (concluded) Resident or
Page 60 and 61: Table 13c. (Concluded) Living Feedi
Page 62 and 63: eelgrass) , while 29 species were f
Page 64 and 65: (239,d9~,9(ii9 kg) (outram and Huln
Page 66 and 67: Washington State Game Dept., pers.
Page 68 and 69: Table 15. Energy in various ccmpart
Page 70 and 71: Export of whole by waterfowl Figure
Page 72 and 73: storms erode and dislodge some eelg
Page 74 and 75: CHAPTER 6 HUMAN IMPACTS-MANAGEMENT
Page 76 and 77:
apparent darnazje. IUllzomes and ro
Page 78 and 79:
great annual range of water tempera
Page 80 and 81:
1978, for all assumptions, formulat
Page 82 and 83:
Table 16. ( CDncluded) Spec ies yea
Page 84 and 85:
REFERENCES Rdarns, S.M. 197va. The
Page 86 and 87:
seagrass community. Pages 153-162 i
Page 88 and 89:
on current flow. Estuarine Coastal
Page 90 and 91:
Inst. Agric. Res., Tohoku Univ.: 13
Page 92 and 93:
In flvt. seayrasses, l'halassia McR
Page 94 and 95:
eelgrass (~ostera marina L. ) Phill
Page 96 and 97:
along the Strait of Juan de Fuca. N
Page 98 and 99:
diatom assemblages in Netarts Bay,
show all

The ecology of eelgrass meadows in the Pacific Northwest: A ...

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?