Woods Hole Oceanographic Institution

Matthew First

»Environmental factors shaping microbial community structure in salt marsh sediments
»The model high molecular weight DOC compound, dextran, is ingested by the benthic ciliate, Uronema marinum, but does not supplement ciliate growth
»Microzooplankton growth and trophic interactions and their effects on herbivory in coastal and offshore environments
»Protistan bacterivory and benthic microbial biomass in an intertidal creek mudflat
»Microzooplankton growth patterns across natural and experimental trophic gradients: Implications for herbivory studies
»Growth and grazing rates of bacteria groups with different apparent DNA content in the Gulf of Mexico

First, M.R., P.J. Lavrentyev and F. J. Jochem , Microzooplankton growth patterns across natural and experimental trophic gradients: Implications for herbivory studies , Marine Biology, 2007

To investigate the growth and grazing patterns of microzooplankton (MZP) in environments of differing productivity, dilution experiments measuring phytoplankton growth (μ) and grazing mortality (m) rates were performed using samples from contrasting locations along the Texas coast. Samples were collected from estuaries, coastal lagoons and offshore Gulf of Mexico locations in the spring and summer of 2001. MZP growth rates were determined in each dilution treatment. Although MZP biomass changed over time in most dilution treatments, adjusting μ and m for the actual grazer gradient (represented by geometric mean MZP biomass) did not cause a significant deviation from the nominal dilution gradient. Likewise, these adjustments did not yield significant regressions where none existed before adjustment. The dynamics of MZP taxonomic groups (ciliates, dinoflagellates) and size categories differed suggesting that in some cases internal predation may lead to trophic cascades. MZP biomass was higher in productive coastal waters and included a larger proportion of dinoflagellates than in the oligotrophic, ciliate-dominated waters of the Gulf of Mexico. The MZP biomass-to-chlorophyll a ratio was lowest in the hypereutrophic Nueces River, where MZP biomass significantly increased in all dilution treatments (net growth rates up to 2 day-1) suggesting a strong top-down control. In the brown-tide dominated Upper Laguna Madre and the oligotrophic seagrass-dominated Lower Laguna Madre MZP growth was decoupled from that of phytoplankton. At these sites, MZP were likely fueled by bacterial carbon and mixotrophy, respectively. Observing the growth response of MZP in dilution experiments can provide insight into trophic structure and efficiency of the microbial food web.

© Woods Hole Oceanographic Institution
All rights reserved