Ecological assessment of anthropogenic impact in marine ecosystems: The case of Bagnoli Bay

Pollutants alter marine systems, interfering with provisioning of ecosystem services; understanding their interaction with ecological communities is therefore critical to inform environmental management. Here we propose a joint compositional- and interaction-based analysis for ecological status assessment and apply it on the benthic communities of the Bagnoli Bay. We found that contamination differentially affects the communities’ composition in the bay, with prokaryotes influenced only by depth, and benthos not following the environmental gradient at all. This result is confirmed by analyses of the community structure, whose network structure suggest fast carbon flow and cycling, especially promoted by nematodes and polychaetes; the benthic prey/predator biomass ratio, adjusted for competition, successfully synthesise the status of predator taxa. We found demersal fish communities to separate into a deep, pelagic-like community, and two shallow communities where a shift from exclusive predators to omnivores occurs, moving from the most polluted to the least polluted sampling units. Finally, our study indicate that indices based on interspecific interactions are better indicators of environmental gradients than those defined based on species composition exclusively.