Dead in the water: The fate of copepod carcasses in the York River estuary, Virginia

Elliott, David T., Courtney K. Harris, and Kam W. Tang

Limnol. Oceanogr., 55(5), 2010, 1821-1834 | DOI: 10.4319/lo.2010.55.5.1821

ABSTRACT: Using laboratory and field experiments we investigated three fates of copepod carcass organic matter in the York River estuary, Virginia: ingestion by planktivores (necrophagy), microbial decomposition, and removal by gravitational settling in the presence of turbulence (sinking). The ctenophore Mnemiopsis leidyi ingested live copepods and carcasses indiscriminately in feeding experiments. Microbial decomposition led to ca. 50% of carcass dry weight loss within 8 h after death. Carcass settling velocities in still water were ca. 0.1 cm s-1, implying short residence time (hours) in the shallow estuary. However, turbulent mixing kept carcasses in suspension much of the time, reducing sinking losses. Rates of carcass organic matter removal were combined in a simple mathematical model predicting the fate of estuarine copepod carcasses. When sinking was considered, it removed a large fraction of carcass organic matter (> 58% for copepodites, > 35% for nauplii), with most of the remainder being removed by microbial decomposition. In the absence of sinking losses, necrophagy became proportionally more important in removing carcass organic matter (> 49%, except in summer).

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