Microbial food web interactions in two Long Island embayments

Phytoplankton mortality (herbivory) and bacterivory were examined experimentally in West Neck Bay and Coecles Harbor, Long Island, NY, from April through September 1998. Small algae (<5 μm diameter) dominated phytoplankton communities in both ecosystems throughout much of the summer, and most microzooplankton (<200 μm) were also small (<40 μm) for that category. Generally, plankton abundances were indicative of eutrophic ecosystems. Oscillations in standing stocks and mortality of prey indicated tight coupling of growth and grazing mortality in both bays. Phytoplankton mortality rates accounted for the removal of 14 to 65% of total phytoplankton standing stocks daily, while bacterivory accounted for the removal of 14 to 88% of total bacterial standing stocks daily. Carbon consumption was estimated from phytoplankton and bacterial removal rates and from conversion to carbon from chlorophyll (phytoplankton) or cell number (bacteria). These calculations indicated that carbon consumption due to bacterivory constituted an average of 21 and 47% of carbon consumption due to herbivory in West Neck Bay and Coecles Harbor, respectively. Total carbon consumption (bacterivory + herbivory) revealed high energy flux through the nano- and microzooplankton assemblages of these estuarine environments.