Coccolithophore communities in the Gulf of Manfredonia(Southern Adriatic Sea): data from water and surface sediments

Living coccolithophore distributions from the Gulf of Manfredonia (Southern Adriatic Sea) were investigated and comparedwith the coccolith assemblages in the underlying surface sediments. In total, 55 samples from 13 stations in four transects collected at the end of October 2000 were analyzed to determine spatial and vertical distribution of individual taxa in the coastal environment. At all stations, the maximum coccosphere densities were between 10m and 30m of water depth (maximum values were ~4x104 coccospheres per litre of seawater). Coccolithophore absolute abundances show a vertical stratification and spatial variation, as well as variable species diversity, increasing from the coast to the open sea and decreasing with depth. Different coccolithophore communities are recorded in the shallow and deep photic zone. Emiliania huxleyi, Syracosphaera spp., Rhabdosphaera spp., Coronosphaera spp., Umbellosphaera tenuis and holococcolithophores are present mainly in the surface waters, above the thermocline between 25-30m depth. In the deeper water samples, there is a significant increase in coccospheres of Florisphaera profunda. The coccolithophore cell density variability is compared with in situ measurements of environmental parameters (temperature, salinity, nitrates and phosphates). Cell densities of all dominant taxa are most highly correlated with temperature variability. The low correlations of cell densities with nitrates and phosphates may be caused by insufficient sampling resolution, nutrient levels close to detection limits, or both. The comparison of the living assemblage with surface sediment records shows significant differences in the presence and abundance of some species. The recognised fossil record in the surface sediments ismainly represented by Cretaceous-Pleistocene reworked species, showing stronger dynamic processes at the bottom, such as terrigenous input and resuspension, than phytoplankton growth. Most marked correspondence between living and fossil assemblages has been found in the deeper and open sea sediments.