Invasive behaviour of the marine Rhodophyta Sphaerococcus coronopifolius Stackhouse, in a hypereutrophic Mediterranean lagoon.

Between 2017 and 2022, sediment labile organic matter, physico-chemical and nutrient content of the water column, biomass and C, N, P, S content of Sphaerococcus coronopifolius, a Rhodophyta that produced vegetative blooms in an area of the Orbetello lagoon (Italy) not far from the effluents of two land-based fish-farms, were examined and compared with an area even further away from that source where the species was not found. In order to understand the reasons for an important mat development in only one specific area, microcosm experiments were also carried out. Results suggest the species developed in dense and extensive mats under high orthophosphate and nitrate nitrogen ion concentrations conditions, behaving as an opportunistic species.

Assessment of the causes of Hg bioaccumulation in the fish of a Mediterranean lagoon subject to environmental management interventions.

In a Mediterranean lagoon characterized by high levels of Hg in the sediment, Hg content in commercial fish species was determined, and, in order to establish Hg concentration in the water column, Diffusive Gradient in Thin films technique (DGT) was used. The results allowed to state (1) the disturbance of the surface sediment and its resuspension in the water column did not cause detectable increase in Hg releases, (2) the East basin acted more than the West one in contamination of fish species, (3) the small-sized sea-breams (<400 g) were more contaminated than larger sizes ones (>400 g). We concluded: (1) fish contamination may also depend on direct contact with releases of the contaminant and small, gregarious and less sedentary subjects are more likely to incur releases of Hg; (2) Hg releases can be greater in areas with a relatively low sedimentary organic matter load compared to areas subjected to high density macroalgal mat, regardless of the amount of Hg present in the sediments; (3) wind transport of plant masses in low energy storage areas, may constitute an increase factor of Hg in the sediment. A critical review of the results was made in comparison with the available literature reports and some hypotheses were proposed regarding the possible dynamics and availability of the contaminant.