Microzooplankton and tintinnid species-specific assemblage structures: patterns of distribution and year-to-year variations in the Weddell Sea (Antarctica)

Abstract

Silicoflagellates, large heterotrophic dinoflagellates, radiolarians, tintinnids and micro- crustaceans were counted in 72 screened (15 urn) samples retrieved at 0-150 m from the Weddell Sea in January 1989. Tintinnid species were identified and biomass estimates were carried out for all groups on the basis of measurements of cell dimensions. Dinoflagellates dominated the micro- heterotrophic community at all stations and depths (65% of overall microzooplanktonic carbon in the 0-150 m interval), followed by the tintinnids (18%), microcrustaceans (16%) and radiolarians (1%). All groups, with the exception of silicoflagell ates, peaked noticeably in the vicinity of the southern end of the transect (76-77°S). Relationships between concentrations of chlorophyll a and microzooplanktonic biomass were present, yet not altogether consistent, but both phyto- and microzooplankton seemed to generally respond to regional enhancements associated with the ice edge. Comparison with similar Weddell and Weddell-Scotia data retrieved in February-March 1987 and November 1988-December 1989, respectively, are highly coherent in terms of microplankton ic abundances, their geographic and vertical distribution patterns, and the specific make-up and distribution of tintinnid assemblages. Analyses of the oral diameters of tintinnid morphotypes suggest that the latitudinal and vertical distribution of their five dominant taxa (which account for >90% of all individuals) is structured so as to maximize resource partitioning.