DYNAMICS OF CILIATE ABUNDANCE, BIOMASS AND COMMUNITY COMPOSITION IN AN OLIGOTROPHIC COASTAL ENVIRONMENT (NW MEDITERRANEAN)

The importance of ciliates as components of the microbial community of the oligotrophic coastal area of the Bay of Blanes (NW Mediterranean Sea) was examined based on a 3 yr, high resolution study focused on th e composition, abundance and biomass of the ciliate community. The mos t abundant components of the ciliate community were 'oligotrich' cilia tes. Naked oligotrichs included heterotrophic genera represented by Ha lteria, Strombidium, Strobilidium, and Lohmaniella, as well as mixotro phic genera represented by Laboea and Tontonia and loricate ciliates r epresented by the group of tintinnids. Autotrophic ciliates were repre sented by the genus Mesodinium. Other, less abundant groups encountere d throughout the study period included the orders Scuticociliatida, Pl eurostomatida and Prorodontida. Ciliate community abundance and biomas s did not show a simple seasonal pattern. Maximum values were observed in spring, following the winter phytoplankton blooms, throughout the study period. Ciliate communities showed significant interannual diffe rences in abundance and cell size. However, total ciliate biomass (mu g C 1(-1)) was similar among years. Changes in ciliate abundance and b iomass were independent of temperature. Periods with persistent, heavy rainfall, which promotes pulses of allochthonous material from flushe d rivers, were characterized by a reduced abundance of ciliates, and i ncreased pico- and nanoplanktonic populations. Cross correlation analy sis revealed that bacterial abundance and chlorophyll a (chi a) concen tration were both significantly negatively correlated with ciliate abu ndance, with time lags of 15 d, suggesting a role for ciliates in the control of these communities. Examination of the variability of ciliat e abundance and biomass at different time scales revealed a dominant s cale of temporal variation in ciliate abundance at about 50 d, similar to that of chi a in the Bay of Blanes, whereas total ciliate biomass (mu g C 1(-1)) did not show any dominant scale of variation.