| I determined biological and chemical composition of <25 μm size fraction seston and its potential value as a potential food resource for suspension feeding ribbed mussels, Geukensia demissa, over five seasons in Canary Creek saltmarsh, Delaware Bay, USA. There were significant seasonal variations in seston components but not in total seston concentration, with percent organic content, particulate organic carbon (POC), particulate organic nitrogen (PON), and chlorophyll a concentration being highest in spring and bacteria and heterotrophic nanoflagellates most abundant in summer. Seston composition also varied within each tidal cycle with a magnitude as great as the seasonal variation. Conversely, seston characteristics did not differ significantly among sampling locations within the marsh, or between samples collected close to the sediment surface and from the upper water column. Microalgae were the most dominant carbon source (62% annually) among the four identified components (phytoplankton, bacteria, heterotrophic nanoflagellates, and cellulose). The total POC in Canary Creek marsh was, however, not associated with any of the 4 identified components. The unidentified components contributed 76% to 92% of total POC in the seston and absorbed by the mussels with modest efficiency (39% and 43%). I suggest that this uncharacterized material was mostly some type of non-lignocellulosic, amorphous detritus that was composed of various sources of particles with different labitity.; Ribbed mussel aquatic respiration rates were determined seasonally and they covaried with body size and season, as the rates were high and strongly related to mussel tissue weight in spring and summer but low and weight independent in winter. The magnitude of seasonal variations of aerial respiration were greater than those for aquatic respiration, and as a result, the ratio of aerial to aquatic respiration was higher in summer than in winter. Ribbed mussel's carbon demand, estimated from rates of both aquatic and aerial respiration, could not be satisfied by any of the 4 identified components in the seston alone. Although total POC exceeded the mussel's carbon requirement in all seasons, I conclude that this unidentified carbon may be an important food source for ribbed mussel populations in the saltmarshes. |
