Living and thanatocoenosis coccolithophore communities in a neritic area of the central Tyrrhenian Sea

The analyses of water and sediment samples, collected at 24 marine stations in a coastal area (Gulf of Gaeta,
central Tyrrhenian Sea) during a three year survey (2012–2014), have improved our knowledge of coccolithophore
ecology in the Mediterranean neritic domain. A comparison between the results and the oceanographic
data has highlighted the ecology of the considered groups, and quantified the relationship between the
community structures and the environmental parameters. The coccosphere concentration measured in the Gulf
of Gaeta is extremely variable over the sampling periods (min:64 l−1; max:2.4*105 l−1), and comparable with
data from other Mediterranean sites. Placolith-bearing taxa are the dominant group of the living communities.
The concentration and distribution of Emiliania huxleyi is controlled by the distance from the coast and the
Volturno River runoff. The K-strategist taxa are an important component of the summer nannoplankton in the
upper 15m and in the sediment samples. These taxa are also related to summer oligotrophic warm waters and
low turbidity as well. The opportunistic behaviour of Helicosphaera carteri is confirmed and is related to moderately
elevated nutrient levels and also tolerance to low salinity and terrigenous input. Nevertheless, our
findings raise some questions on the reliability of H. carteri as a low salinity proxy. Overall, the sediment assemblages
reflect the composition and the temporal distribution of the living communities. The occurrence and
distribution of abundant reworked coccoliths, both in water and sediments, provides useful information about
coastal dynamics and confirm their use as a reliable runoff proxy.