Spatial and temporal variation of phytoplankton community structure in a coastal marine system subjected to human pressure

Human use of the world's seas and oceans is causing cumulative pressures on, and changes to, coastal marine habitats. The Gulf of Pozzuoli (GoP) is one of the three marginal sub-basins identifiable in the Gulf of Naples which have been affected by strong anthropogenic pressure since the end of the 19th century. While several studies demonstrated sediment and water contamination in the GoP, to date, few and fragmented data have described the effects on the phytoplankton community in such a coastal system. In order to contribute to a more detailed picture of the ecological status of the GoP, we have analysed the phytoplankton community in terms of biomass and functional diversity, particularly in relation to water salinity and nutrient availability. Our results reveal the presence of two different trophic areas in the GoP. The first one is located in the eastern sector, which is more sensitive to land run-off and characterized by a higher level of biomass. The second one is situated in the western sector, and is characterized by a higher salinity and lower level of biomass. Diatoms and haptophytes were the most representative groups; other minor groups showed higher spatial and temporal variability, especially in coastal stations. The weakening gradient of salinity from the coast to open water and the point distribution of nutrients suggest that the GoP is affected by scattered anthropogenic sources, the contribution of which to the overall system is irregular and depends on dilution dynamics. Despite this, the GoP presents mean Chl a concentrations similar to those of oligotrophic environments, and, the high variability observed underlines the importance of applying the appropriate sampling scales to measure coastal systems subject to point anthropogenic pressures.