GEOGRAPHIC-DISTRIBUTION OF LIVING AND HOLOCENE COCCOLITHOPHORES IN THE MEDITERRANEAN-SEA

The distribution patterns of living coccolithophores in the Mediterran ean Sea during September-October, 1986 and February-March, 1988 were i nvestigated and compared with the coccolith assemblages in the underly ing surface sediments. The highest coccolithophore production was obse rved during late winter, when maximum cell densities in the upper wate r column reached 2.3 X 10(5) individuals per liter, which is more than 5 to 10 times the average concentration in summer. During February to March 1988 E. huxleyi dominated the community and probably was close to bloom conditions in the Eastern Mediterranean Sea. Although these f luctuations in the living flora between September-October and February -March represent snapshots during the seasonal succession-cycle of the coccolithophore flora in the Mediterranean Sea, they are interpreted to be related to seasonal, wind-induced hydrological changes from a hi ghly stratified upper water mass during summer to a homogenized waterc olumn during winter. The enrichment of E. huxleyi in the surface sedim ents suggests, that this species probably produces regular blooms in s urface waters during late winter or spring in that area. The rather co nsistent abundance of the deep dwelling species Florisphaera profunda in the surface sediments may be related to the less pronounced seasona lity in the lower photic zone. Although most of the observed geographi c change in the taxonomic composition in either of the two plankton da ta sets are due to seasonal and daily to weekly fluctuations of the co ccolithophorid populations, at least in one species, Gephyrocapsa ocea nica, a relationship to surface currents was found. This species proba bly enters the Mediterranean Sea through the Strait of Gibraltar and i s a tracer for Atlantic surface waters. Other species that preferencia lly occurred in the Western Mediterranean Sea are Gephyrocapsa ericson ii and Gephyrocapsa protohuxleyi, but relationships to surface cur-ren ts were less clear.