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

More documents

Recommendations

Info

Washington State Game Dept., pers. comm., 1982), with spring counts averaging 47,392 birds (up to 58% oE the Pacific Flyway passes through Padilla ~ay). An average of 50,rilBB ducks winter on Padilla and nearby Samish Bays (over 6,LMB are diving ducks: canvasbacks, scaup, go ldeneyes, buffleheads, and scoters on ~adilla Bay alone; several of these species feed on eelgrass or animals within the system). In northern Puget Somld, Sitnenstad et al. (1979) recorded that the principal wintering sites for black brant were Padilla Bay, Samish Ray, Discovery Bay, and Sequiln Bay. In April up to 18,00U brant were recorded in Siunish Bay, 55,Om in Padilla Bay, and 6,000 in Discovery Bay At Grays Harbor an estimated 5(21,00U ducks and 6,000 brant use the estuary during winter (Proctor et al. 1990b). Grays Harbor also supports more than 150,01dU shorebirds during peak migrations and is an important link in their migration (ACOE 1977b). In Willapa Bay, 50,000 black brant overwinter (proctor et al. 1980b). Only 1,500-2,2l30 brant overwintered in 1981-82 (Washington State Game Dept., pers. comm., 1982). At peak periods Willapa Bay harbors 200,O(a0 or more waterfowl. It is known rmw that Willapa Bay and Humboldt Bay are important wintering areas for the canvasback duck (850 winter in Willapa Bay with peak populations at 1,4II0 to 1,600; Proctor et dl. 1980a,b). Wintering populations of ducks in Humboldt Bay are 124,000 with an additional 35,000 black brant. In the Yaquina estuary, black brant arrive in late October-ear 1 y November, increase in numbers to 350-525 birds in mid- January, and further increase to 780-914 birds in late March (R.D. Bayer, pers. ccmn., 1983). Tfius, there is a large list of birds that directly eat or are dependent on eelgrass and its food webs ee able 14). The nutrient and energy flows that these birds control and drive are emrimus in scope. 4.8 TROPHIC RELATIONSHIPS AND GENERAL mum As with all the world's ecosystems, the eelgrass system supports both grazing and detrital food webs. Owing to the high prductivity of eelgrdss and its sloughing of leaf material from the shoots, a third pathway of energy flow is evident, that of leaf and detrital exprt. Recent work in the tropics has documented the increasing importance of the direct: use of leaves and epiphytes (grazing, herbivory), but in seayrasses generally and eelgrass in particular, the detrital food webs within the eelgrass meadows are still the primary pathway of trophic energy transfer (Kikuchi 1980). Very few organisms use the fresh eelgrass plants in the Pacific Northwest as food. Table 14 lists the waterfowl which are overwhelmingly the dominant grazers on eelgrass in the region. McRoy and Helfferich (1980) listed only the green urchin, Stronglyvcentrotus drobachiensis, which consma2 fresh eelgrass. It would be useful to have abundant data on the amount of energy or production which is channeled through direct herbivory, the detritaL E d webs, and the export route. Unfortunately, only the old study done by Petersen (1918) in Denmark and the relatively recent one conducted by Thayer et al. (1975b) have documented the energy flows quantitatively. Thayer et al. (1975b) concluded that the eelgrass system exports to adjacent systems, on the basis of a net incrase of sedirnent carbon, but no direct work was done. They also calculated that the macrofauna in the eelgrass bed in North Carolina consumed energy equivalent to 55% of the net prduction of eelgrass, phytoplankton, and benthic algae in the bed. 'hey calculated a gross-growth ecological efficiency of 12% for the macrofauna in the bed and 24% for the fish community, suggesting a fairly efficient system with a surplus of energy to support the food webs. The high efficiency for the fish, in large measure a result of high proportions of juveniles in the community, suggests that the eelgrass system provides resident fish with superior shelter, food, and protection. These fish probably spend a relatively small proportion of their energy coping with environmental extremes, searching for food, and escaping from predators, and can use a relatively large part of their consumed energy for growth
Table 14. waterfowl that use eelgrass meadows in the Pacific Northwest. Species Location Winter wlation Spring population Food Black brant padilla 5,000 samish Bay -- Discovery Bay - Grays Harbor 6,000 Willap Bay 50, Wa0 Yaquina Estuary 350-525 Humboldt Bay 35,000 Eelgrass vegetation ,I Ducks Padilla arid Samish 50,000 (6,000 are Bays diving ducks ) Grays Harbor 50,800 Willapa Bay Canvasback duck 850 Humkoldt Bay 124,000 Shorebirds Grays arbor -- Miscellaneous Canada geese Elnperor geese American wigeon Scoters (3 species) Coots Canvasback Ring-neck Bufflehead Ruddy Pintail Mallards Green-wing teal scaups (2 species) Eelgrass vegetation or animal life on or mng the plants 8 Eelgrass vegetation Eelgrass vegetation or animal life on or am~q the plants Animal Life on or mng the plants Eelgrass vegetation Eelgrass vegatntion; herring eggs Eelgrass vegetation Eelgrass vegetation Eelgrass seeds; epi f dUM Eelgrass seeds; epi fauna Eelgrass seeds; epi fauna Eelgrass vegetation; fauna shelters 200,0!30 or more waterfowl at peak periods. and production. Figure 11 shows the proportional relations of the various trophic compnents in this North Carolina eelgrass system (Thayer et al. 1975b). Table 15 lists the various compartments in this system and the energy relations involved. Finally, an abundant literature has documented the role of eelgrass as a nursery for young fish and many other animals (~hayer et al. 1975b; Adarns, 197Ga,b; Thayer and Phillips 1977; Thayer et al. 1979; ; Kikuchi 1980; McKoy and Helfferich 1980; Orth and Heck 1980). The meadow actually is a giant fwd factory, feeding a small number of herbivores, with most of the primary prduction decaying to enter the detrital food webs. Owing to the density of foliage and sediment stabilization, the habitat also becomes a refuge for many other animals. Thus, the meadow attracts permanent, seasonal, and
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 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 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 ...

Create successful ePaper yourself

Delete template?

Save as template?