Coccolithophores from near the Volturno estuary (central Tyrrhenian Sea)

Abstract

We present the distribution pattern of living and surface sediment coccolithophores, the main phytoplankton calcifying group, from 22 stations set in a neritic environment (from 10 to 50 m water depth), adjacent to the shelf area of the Volturno River mouth (Gulf of Gaeta — central part of the Tyrrhenian Sea). The survey conducted in June 2012 included five transects perpendicular to the coast, which enabled us to provide indications on the structure of calcareous phytoplankton associations in relation to coastal dynamics and the Volturno River runoff. The total number of coccospheres ranged from 15 to 64 ∗ 103 ∗ l− 1 coccolithophores. Emiliania huxleyi dominates the assemblages, followed by Rhabdosphaera xiphos, holococcolithophores and Syracosphaera pulchra. The coccolithophore community shows a typical vertical zonation, with K-strategist taxa in the upper 15 m and the deep community developed down to 40 m. The local water circulation significantly affects the spatial and vertical distribution of coccolithophores. The river discharge influences the distribution of coccolithophore taxa, resulting in a north–south gradient. In the northern sector, outside the influence of the Volturno River, the high values of R. xiphos suggest a negative correlation with river runoff. The surface sediment assemblages reflect the overall composition of the living coccolithophore communities. The distribution of abundant reworked species, both in water and sediment, provides useful information about coastal dynamics and sediment transport in the study area.