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

Microzooplankton abundance, biomass and composition were investigated in th e coastal waters of Asturias (southern Bay of Biscay) in May 1996. Abundanc e ranged from 0.7 x 10(3) to 8.5 x 10(3) cell.L-1 The protists community wa s dominated by aloricate ciliates averaging 82 % of microheterotrophs. Smal l aloricate ciliates, below 20 mu m in size, contributed 63 % to total cili ate abundance. Carbon biomass ranged from 2.4 to 15.4 mgC.m(-3), averaging 23 % of phytoplankton biomass. Aloricate ciliates were also the dominant co mponent of biomass (56.2 %), but the importance of copepod nauplii increase d in terms of carbon, averaging 28.5 % of total biomass. Microzooplankton b iomass was significantly correlated with Chi a concentration in the water c olumn. 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. Cho reotrich ciliates were the most important potential grazers in the study (1 3.7% of standing stock) followed by metazoan nauplii (6.3 %). The potential microzooplankton impact on phytoplankton was consistent with the large siz e of primary producers during diatom spring blooms, like the one found in t his study. The validity of theoretical estimates of microzooplankton grazin g impact, as well as the importance of including metazoan larvae in coastal microzooplankton community studies are discussed. (C) 2000 Ifremer/CNRS/IR D/Editions scientifiques et medicales Elsevier SAS.