Field observations of the polychaete Mesochaetopterus taylori Potts, 1914, indicated facultative deposit feeding was elicited by tidal variations. Two distinct types of M. taylori egesta were observed, usually as part of the same fecal coil: mucus-packaged brown pellets,
and gray coils that resembled surrounding sediment deposits in color and texture. Our goal was to compare bacterial and microalgal communities from brown and gray egesta, surface sediments, deep (∼5 cm) sediments, and the benthic nepheloid layer collected from sandflats in North Inlet,
South Carolina. Bacterial and diatom assemblages were compared through denaturing gradient gel electrophoresis fingerprinting. Epifluorescence microscopy was used to enumerate bacteria and fluorometric quantification of chlorophyll a was employed as a proxy for microalgal biomass. Microbiological
evidence, combined with field observations and granulometric data, confirmed that gray coils were derived primarily from subsurface sediments during deposit feeding at low tide, with a smaller contribution from surface (top 2 mm) deposits. Microbiota in brown egesta showed overlap with microbial
assemblages in both the nepheloid layer and uppermost sediment layers at low tide. Microalgal biomass was removed during gut transit; however, the quantitative effect on bacteria was less clear due to selective feeding, digestion, and potential growth within the gut. Although brown and gray
coils were distinct, there was a clear “gut signature” such that egesta had microbiological similarities regardless of provenance. Thus, the net effect of M. taylori on sedimentary microbial structure is substantial, as it both digestively removes specific microbiota and
reduces diversity while deposit feeding, yet introduces species to sediments by pelletizing suspended particulates.
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