Spring microzooplankton composition, biomass and potential grazing in the central Cantabrian coast (southern Bay of Biscay)

Abstract

Microzooplankton abundance, biomass and composition were investigated in the coastal waters of Asturias (southern Bay of Biscay) in May 1996. Abundance ranged from 0.7×10 3 to 8.5×10 3 cell·L −1. The protists community was dominated by aloricate ciliates averaging 82 % of microheterotrophs. Small aloricate ciliates, below 20 μm in size, contributed 63 % to total ciliate abundance. Carbon biomass ranged from 2.4 to 15.4 mgC·m −3, averaging 23 % of phytoplankton biomass. Aloricate ciliates were also the dominant component of biomass (56.2 %), but the importance of copepod nauplii increased in terms of carbon, averaging 28.5 % of total biomass. Microzooplankton biomass was significantly correlated with Chl a concentration in the water column. Theoretical estimates of the grazing impact of the microzooplankton community on phytoplankton were calculated and resulted in an average value of 28.3 % of phytoplankton standing stock potentially consumed per day. Choreotrich ciliates were the most important potential grazers in the study (13.7 % of standing stock) followed by metazoan nauplii (6.3 %). The potential microzooplankton impact on phytoplankton was consistent with the large size of primary producers during diatom spring blooms, like the one found in this study. The validity of theoretical estimates of microzooplankton grazing impact, as well as the importance of including metazoan larvae in coastal microzooplankton community studies are discussed. © 2000 Ifremer/CNRS/IRD/Éditions scientifiques et médicales Elsevier SAS microzooplankton / ciliates / biomass / grazing / southern Bay of Biscay