ECOLOGY OF BUZZARDS BAY: An Estuarine Profile 



65 



Table 4.10. Average biomass and release of ammonia into marsh waters during summer 

 by major marsh organisms Biomass of mollusks excludes the shell weight; plant biomass 

 aboveground only Excretion proceeds for 12 h/day for Geukensia, 24 h/day for other 

 species Data from Jordan and Valiela (1982). 



■■Excretion assumed equal to that of G demissa 

 "Excretion assumed equal to that ot C maenas 

 'Excretion assumed equal to that of / obsoleta 



byssal threads produced by these mussels increases 

 the coherence of their substrate (Davis 1 985) and 

 may, along with belowground roots and rhizomes, 

 stabilize marsh peat, especially areas along 

 creekbanks. In areas with high levels of contami- 

 nants like polychlorinated biphenyls (PCB"s) and 

 metals in the water column (such as found in the 

 Acushnet River estuary), the deposition of 

 pseudofeces from fdtration of organically bound 

 contaminants increases the levels of these 

 contaminants in the surface sediments of the marsh. 

 Studies by Jordan and Valiela ( 1 982) indicate 

 that ribbed mussels play an important role in the 

 nitrogen cycle of coastal salt marshes. Nitrogen fil- 

 tered but not deposited by ribbed mussels is ex- 

 creted as ammonia or dissolved organic nitrogen, 

 or used for production of flesh, shell, byssal threads, 



or gametes. The resident ribbed mussel population 

 in Great Sippewissett Salt Marsh (West Falmouth) 

 was found to maintain the highest biomass of any 

 animal population, releasing more ammonia into the 

 water than any population of plants or animals (Table 

 4. 1 0), and accounting for 3 1 % of the ammonia re- 

 leased into tidal waters during summer. Most of this 

 ammonia is presumed to be taken up by phy- 

 toplankton or edaphic diatoms, bacteria, and fungi 

 growing on Spartina detritus, as the overall am- 

 monia concentration in tidal waters remains rela- 

 tively unchanged. The population of ribbed mus- 

 sels in Great Sippewissett was calculated to theo- 

 retically filter all of the water in each tidal cycle, 

 although they presumably refilter water in their ad- 

 jacent vicinity. Their biggest role in the nitrogen cycle 

 of salt marshes is the retention of nitrogen within 



