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

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The terms used to describe biomass will follow the definitions in Zieman and Wetzel (1980): standing crop refers to above-sediment material, while biomass refers to the weiyht of all living plant material. mth are expressed as mask per unit area. Representative densities are reported, but density can vary seasonally, with depth, and with substrate nutrients and texture. A few values w i l l be listed for comparative purposes able 7). As with density values, biomass also varies widely. It appears that the pattern first noted by Ostenfeld (1908) of decreased density on firm sand and increased density on softer substrates may be the only correlation possible. Most of the biomass of eelgrass is in the sediments. Depending on the season, the ratio of 1eaves:rhizomes-roots varies from 1: 1 in summer to 1:2 or greater in winter in Puget Sound (Phillips 1972). These same ratios were found in eelgrass in Denmark (Sand-Jensen 1975 ). In Long Island, New York, Burkholder and Doheny (1968) found eelgrass leaf-shoot:rhizome ratios of 2:3 in sand and 10:3 in mud. In southern British Columbia, Canada, eelgrass ratios varied from 0.8 to 1.6 (~arrison 1982~). He has made the only analysis of 1eaf:rhizome-root ratios in Z, a onica (2.0-2.6). Recently, Kenworthy f-r 1981 also reported a shift in 1eaf:root ratios from those in favor of leaves to roots with a shift in substrates from mud to coarse sand. Kentula (1983) reported leaf-shoot: rhizome-root ratios varying from 1:l to 1:10 along intertidal transects of eelgrass in Netarts Bay, Oregon. In one study, Smith et al. (1979) determined that eelgrass root and roo hair surface areas were 48.2 and 138.9 mm 5 root, respectively. In the tropical colonizing species Halodule wrightii, the root and root-hair surface areas were 34.8 and 19.2 mix2 root, respectively. In Table 7 only standing crops will be reported. The smallest seagrass standing crop was 6g dry wgt/rn2 in Humboldt Bay, California (waddell 1964), while the highest value was 2,@60 dry wgt/m2 (~urkholder and Doheny 1968). Work done to date implies that biomass parameters reflect the nature of the substrate. Caloric values of eelgrass tissue have only rarely been reported. In North Carolina, caloric values ranged from 3.54 cal/mg ash-free dry wt in January to 4.82 cal/mg ash-free dry wt in June to 5.73 cal/mg ash- f ree dry wt from Apr il-May during flowering (annual mean was 4.48 cal/mg; Thayer et al. 1975b). There was seasonal variation noted. In Izembek Lagoon, Alaska, McRoy (1966) reported a mean of 4.125 cal/mg ash-free dry wt for leaves and 3.967 cal/mg ash-free dry wt for rhizomes. 3.3 PROCUCI'IVITY AND MEASlJWPEER A number of reports have documented seagrass meadows as one of the richest arid most productive of ecosystems, rivaling cultivated tropical agriculture in productivity (summarized by Zieman and Wetzel 1980). The earliest work to relate the value of eelgrass to inshore ecosystems was the work of Petersen (1891, 1913, 1918) and coworkers at the Danish Marine Biological Station (Petersen and Boysen-Jensen 1911; Ostenfeld 1908; Boysen-Jensen 1914; Blegvad 1914, 1916). These scientists concluded that organic detritus, derived chiefly frorn the decay of eelgrass, was the basic source of nutrition of animals in Danish coastal waters, especially the benthic invertebrates and that the abundance of fish in Denmark was due chiefly to eelgrass. Estimates have shown that eelgrass can attain productivities up to 8 g~/m2/da and an annual production of 500 g~/m 2' . Several factors are directly correlated with eelgrass productivity: light, temperature, carbon supply, nutrient supply, and plant density. Thus, there are hourly, daily, and seasonal differences at local sites as well as over a geographic gradient. In addition, methds of analyzing productivity vary in reliability from leaf marking (Zieman 19681, 14C uptake i it taker and Iverson 1976), harvest method (Petersen 1913; Phillips 1972; Mukai et al. 1979), to relating biomass to the plastochrone interval (P.I.; Patriquin 1973; Jacobs 1979). No
2 Table 7. Representative eelgrass density and standing crop (g dry wt/m ). Numbers represent means for stations sampled. Species Location No. of veg. No. of repro. Standing crop Source shoots/n shmts/n Zostera Mexico 0 555 (April) mrina Gulf of California California Hunboldt Bay 31-361 -- Oregon Yaquina Bay 17-913 (less 209 at MUM: greatest at higher elevations) Phillips et al. 1983b Keller 1963, Waddell 1964, Keller and Harris 1966 Harding ad Butler 1979 Bayer 1979a Netarts Bay 500-3,845 5-65 7-256 Kentu1.a 1983 Washington Grays Harbor 74 -- -- Smith 1976 Hccd Canal 62-287 7-10 -- Phillips et al. 1983b Whidbey island 71-861 5-66 95-540 Phillips 1972, Phillips et al. 1983b So. British Colunbia 25-150 1-18 4-88(bianass)Mady 1978, Harrison 1982c Alaska Various locations 243-650 4-100 -- Phillips et al. 1983b Iz&k Lagoon 740-4,380 48-653 186-1,840 North Carolina -- -- 50-550 Dillon 1971, Thayer et al. 1975a, Penhale 1977, Phillips et al. 1983b New York .- -- 250-2,060 Burkholder and Doheny 1968 Rhde Island 629-2,044 67 -- Phillips et al. 1983b Canada - Z. japonica So. Brltish Colunbia 160-450 70-150 4-20 (bionass)~arrison 1982c
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 26 and 27: leaves overtopped them and created
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 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,
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