Food web interactions in the plankton of Long Island bays, with preliminary observations on brown tide effects

Abstract

We examined the relative importance of phytoplankton and ciliates as prey for metazoan zooplankton, and the role of predation in regulating ciliate populations in 2 Long Island (USA) bays. Depth-integrated primary production (mg C m-2 h-1) was dominated by nannoplanklon <5 μm in diameter throughout the year, ranging from > 95% of total production in mid- summer to an average of about 60% in winter and early spring. Predator exclusion and addition experiments conducted in microcosms showed that the mortality coefficient of ciliates (d-1) from zooplankton predation was higher when larger phytoplankton (> 10 μm) contributed less to total primary productivity. For adult copepods, an increase in the percentage ciliate contribution compared to phytoplankton contribution to total carbon intake also coincided with the higher percentages of small microalgal production. Egg production rates of Acartia spp. were positively correlated to the net growth coefficient of ciliates. In contrast, micrometazoa routinely obtained >70% of their total carbon ration from phytoplankton, and at times during spring and summer, removed 23 to 52% of the total depth-integrated primary production. In addition to protozoa, we suggest that micrometazoa, particularly copepod nauphi, may serve as a trophic link between phytoplankton and mesozooplankton in Long Island bays.