Date Awarded


Document Type


Degree Name

Master of Science (M.Sc.)


Virginia Institute of Marine Science


Deborah K. Steinberg

Committee Member

Mark J. Brush

Committee Member

Carl T. Friedrichs

Committee Member

Marjorie A.M. Friedrichs


The biological pump is a critical component of carbon transformation in aquatic ecosystems, but the role that zooplankton play in carbon production and vertical export is rarely studied in estuaries. Zooplankton produce carbon-rich fecal pellets which sink to depth and can fuel benthic community metabolism. The body size and taxonomic structure of the zooplankton community varies on interannual, seasonal, and diel time scales, and can lead to varying carbon production and export rates. We quantified fecal pellet carbon (FPC) production by the whole mesozooplankton community (> 200 µm) in the York River, a sub-estuary of Chesapeake Bay. Biomass and taxonomic composition of the near-surface zooplankton community was measured with paired day/night net tows conducted monthly over one year (Jun. 2019 - Nov. 2020). We also conducted live experiments to quantify FPC production rates of both the (size-fractionated) whole community and of dominant individual taxa. Zooplankton biomass generally increased in surface waters at night (2 to 29-fold) due to diel vertical migration. Biomass was low in the winter and high in the summer, with a peak in gelatinous zooplankton biomass in summer the most conspicuous seasonal shift in community composition. Acartia spp. copepods were consistently the most abundant taxon, with cladocerans and barnacle nauplii becoming equally abundant in the winter and spring. Whole community FPC production rates were higher (3- to 65-fold) at night than during the day. This was driven by increases in mesozooplankton biomass, especially Acartia spp., at night due to diel vertical migration, with the 0.5 – 1 mm size class comprised of Acartia spp. contributing 2-26% to FPC production in the day versus 40-70% at night. Daytime FPC production was dominated by the two smallest mesozooplankton size fractions - comprised mostly of Acartia and other copepods, barnacle nauplii, rotifers, and cladocerans. Increases in the relative contribution of larger size fractions to total FPC production occurred at night due to diel vertical migration into surface waters of larger animals such as mysids, which produced relatively large and carbon-rich fecal pellets. Seasonal estimates of community FPC production were highest in the fall, intermediate in the spring, and lowest in the summer. Surface FPC production was affected by seasonal shifts in the mesozooplankton community, including increases in the abundance of large migrating animals (mysids, chaetognaths, larval fishes) in the summer and relatively larger calanoid copepods in the fall. Gelatinous zooplankton may have contributed a top-down control limiting community FPC production rates in the summer. This study indicates that zooplankton FPC production in estuaries can surpass that in oceanic systems. Future research on the fate of fecal pellets produced in the surface is needed to understand the role of fecal pellets in vertical carbon export and benthic-pelagic coupling in the York River and other estuaries.




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