ctenophore populations (Nelson 1925). He- 

 roplankton usually compose a greater por- 

 tion of the zooplankton community during 

 summertime when many clams, mussels, oys- 

 ters, barnacles, crabs, polychaetes, and 

 other benthic organisms are spawning. This 

 input of living protein from the bottom 

 into the water significantly increases the 

 food supply of filter-feeding animals, 

 both nektonic and epibenthic suspension 

 feeders. Many of the latter probably can- 

 nibalize larvae of their own kind. 



Nekton 



The active swimmers in the estuary 

 are divided into pelagic and demersal nek- 

 ton. The pelagic nekton feeds in the 

 water column, either on phytoplankton and 

 detritus, on zooplankton (including oyster 

 larvae), or on other nektonic forms. The 

 bottom feeders or demersal nekton feed on 

 adult benthos, including oysters and their 

 associates. Darnell (1961) reported the 



feeding habits of some typical estuarine 

 nekton (Figure 5). 



Terrestrial Consumers 



The other major group of consumers 

 characteristic of the marsh-estuarine sys- 

 tem is the large, diverse collection of 

 "terrestrial" or land-based consumers. 

 This group comprises insects and other 

 small arthropods, including some fiddler 

 crabs; pulmonate gastropods, especially 

 Littorina irrorata ; birds; reptiles (even 

 alligators); and mammals, such as the rice 

 rat, mink, otter, and raccoon. The spe- 

 cific members of this group that directly 

 impinge on the oyster reef community are 

 discussed in Chapter 3. The total biomass 

 of terrestrial consumers, including the 

 active primary consumers (plant hoppers 

 and grasshoppers) that graze Spartina di- 

 rectly, was estimated at 1 g C/m2 (Pomeroy 

 and Wiegert 1980). 



- ••---- M, *^ 



--'-^.T-v^-*;'' 



h^'W 



.^^•-"W^. 



^ %==■ 



^c; -- 



i-L^ -^ »:^ ** 





'2: 



•fM- 



A view of the estuarine environment in which oyster reefs occur in coastal South 

 Carolina. Photo by South Carolina Wildlife and Marine Resources Department. 



14 



