The Role of Zooplankton Community Composition in Fecal Pellet Carbon Production in the York River Estuary, Chesapeake Bay.

Zooplankton play a key role in the cycling of carbon in aquatic ecosystems, yet their production of carbon-rich fecal pellets, which sink to depth and can fuel benthic community metabolism, is rarely quantified in estuaries. We measured fecal pellet carbon (FPC) production by the whole near-surface mesozooplankton community in the York River sub-estuary of Chesapeake Bay. Zooplankton biomass and taxonomic composition were measured with monthly paired day/night net tows. Live animal experiments were used to quantify FPC production rates of the whole community and dominant individual taxa. Zooplankton biomass increased in surface waters at night (2- to 29-fold) due to diel vertical migration, especially by Acartia spp. copepods. Biomass and diversity were seasonally low in the winter and high in the summer and often dominated by Acartia copepods. Whole community FPC production rates were higher (3- to 65-fold) at night than during the day, with the 0.5-1 mm size class contributing 2-26% to FPC production in the day versus 40-70% at night. An increase in the relative contribution of larger size fractions to total FPC production occurred at night due to diel vertical migration of larger animals into surface waters. Community FPC production was highest in fall due to increased diversity and abundance of larger animals producing larger fecal pellets, and lowest in summer likely due to top-down control of abundant crustacean taxa by gelatinous predators. This study indicates that zooplankton FPC production in estuaries can surpass that in oceanic systems and suggests that fecal pellet export is important in benthic-pelagic coupling in estuaries.

Supplementary information: The online version contains supplementary material available at 10.1007/s12237-024-01442-8.