until later. Macro-infauna are often di- 

 vided into two functional groups, deposit 

 feeders and suspension feeders. Theories 

 have been developed to explain why often 

 the two groups appear to be mutually ex- 

 clusive in local areas (Rhoads and Young 

 1970; Levinton 1972). 



Suspension feeders include clams and 

 sone tube-dwelling polychaetes (worms). 

 Deposit feeders are often more motile, and 

 some workers even include in the group 

 those quasidemersal nektonic organisms 

 that burrow into the bottom to feed, e.g., 

 grass shrimp. Kany polychaetes and gas- 

 tropods (snails) are also deposit feeders. 

 Another major category of the estuarine 

 macrobenthic community is the predators, 

 including some gastropods, turbellarians 

 (flatworms), nemertines (round worms), and 

 echinoderms (starfish). 



Deposit feeders and demersal nekton 

 are important in reworking the sediments 

 by burrowing and plowing (bioturbation). 

 This activity redistributes organic matter 

 and other nutrients to the water column 

 and introduces oxygen into the sediments. 

 For example, one mullet can rework 45 m^ 

 of bottom area per year (Pomeroy and 

 Wiegert 198G). 



Conversely, suspension feeders (in- 

 cluding oysters) filter particles from the 

 water column and then deposit organic miat- 

 ter in the form of feces on the sediment 

 where it becomes available to the decom- 

 posers. Krauter (1976) estimated that salt 

 marsh macrobenthic organisms (in the marsh 

 proper) deposit 1,709 g dry wt/m-^/ yr, 

 which is 455 g of organic matter. He also 

 calculated that 53% of the marsh's annual 

 primary production could be processed 

 through the feeding mechanisms of these 

 organisms. 



Zooplankton 



Estuarine animals living suspended in 

 the water column generally are classified 

 as zooplankton if they are either so small 

 or such weak swimmers that they are trans- 

 ported passively by water currents. The 

 mobility of zooplankton typically is lim- 

 ited to vertical migrations in the water 

 column; for example, a daily migration 

 from the surface to bottom waters and back 

 again is a commonly observed pattern among 



many forms. By altering their vertical 

 elevation in the water column, zooplank- 

 ters can use variations in food supply and 

 use water movements in estuaries for dis- 

 persion by "riding" parcels of water mas- 

 ses as the latter traverse an estuary. 

 For example, some species of zooplankton 

 follow the salinity wedge on the bottom as 

 the wedge progresses landward, or the sur- 

 face layers of freshwater as they move 

 seaward. 



Zooplankton often are divided into 

 holoplankton and meroplankton. Holoplank- 

 ton spend their entire life cycles in the 

 water column while meroplankton spend only 

 their larval stages above the bottom. 

 Holoplankton include microzooplankton, 

 such as copepods and rotifers; and macro- 

 zooplankton, like euphausiids, ctenophora 

 and other jellyfish. Meroplankton include 

 larval finfish and decapods; and a large 

 contingent of the larvae of many macroben- 

 thic animals, including many polychaetes, 

 barnacles, clars and mussels, and, of 

 course, oyster larvae. 



The functional importance of zoo- 

 plankton in the estuarine ecosystem is 

 partly expressed by a high turnover rate 

 of planktonic species, by large popula- 

 tions, and by the very small average size 

 of individual members. These three fac- 

 tors ensure that zooplankton process a 

 large amount of the organic materials 

 available in some estuaries, much of which 

 represent the conversion of phytoplankton 

 into the tissue of higher consumers. The 

 zooplankton community as a group largely 

 depends on phytoplankton as a carbon 

 source, and thus tends to be more impor- 

 tant (abundant) in estuaries dominated by 

 phytoplankton, rather than in those where 

 macrophyte production is of primary impor- 

 tance. The carbon pathway from phytoplank- 

 ton to zooplankton to higher consumers is 

 a significant trophic link in all estua- 

 ries, however, including those in the 

 study area. 



Although the oyster larvae are mem- 

 bers of the zooplankton community, they 

 are extremely vulnerable to predation by 

 plankton feeders, including members of the 

 macroplankton group, such as ctenophores. 

 Some years ago in the New Jersey oyster 

 grounds, oyster spatfall (larval recruit- 

 ment) was reduced during years of large 



13 



