Hydrothermal effect on fish biodiversity in Panarea Islands (Tyrrhenian Sea, Mediterranean)

The Aeolian Archipelago is a complex volcanic system constituted by seven islands and seamounts in the central Mediterranean (southern Tyrrhenian sea) and characterized by an active submarine hydrothermalism due to the presence of volcanoes, submarine canyons and hydrothermal sources. At the end of October 2002, three kilometers East from the island near the islet of Bottaro, a violent submarine gas eruption occurred. In the same period, after one month, a paroxysmal activity (a violent eruptive manifestation of the volcano) was observed in the Stromboli Island. This explosive event ejected incandescent scoria and booms fall out up to a distance of few kilometers from craters. Biodiversity associated with hydrothermal event was studied by integrating different methods. More in detail, fishing surveys and underwater visual census (UVC) by means of SCUBA divers were employed. Underwater visual census has underlined an immediate effect on the local habitat related to the noise, water heating, gas emission (CO2 and H2S), with braking away and dead of fish. The effects on biocenosis were observed for the next months on infralitoral and the associated community. The biocenosis ricolonization was observed the year after. Long term effects were related to the potential harmful trace elements (PHE), such as mercury (Hg), cadmium (Cd), lead (Pb), and arsenic (As). Rocks and sediments could release different trace elements, including PHE, when they are leached by hot fluids such as gas and hot waters which determine emissions at high temperature (around 30 and 130 °C). Sedentary benthonic fishes with longevity characteristics have been chosen in order to give a better description of the site investigated and the bioaccumulation phenomenon. Liver and muscle of the bluemouth rockfish Helicolenus dactylopterus dactylopterus (Delaroche, 1809) and the comber Serranus cabrilla (Linnaeus, 1758) were analyzed. Cd, and Pb determinations were performed by atomic absorption spectrometry with electrochemical atomization (GFAAS, Perkin-Elmer, mod. Analyst 700). Hg, and As were determined by atomic absorption via cold vapor generation (CV-AAS), according to the US-EPA 7473, and by atomic absorption after the hydride generation following the US-EPA 7011 method, respectively. A high trend of bioaccumulation was observed in selected species with the occurrence of higher levels after ten months from the event; observed higher levels in fisher were reliable to the growth rates as evidenced by the lower BEF observed after ten months; different species evidenced different bioaccumulation behavior, principally related to the trophic level and the diet of the species. Even though volcanic contribution seems to be of a little importance for most trace elements on a global scale, volcanic-derived emissions may become important in areas characterized by active volcanism which could represent local hot-spots of particular importance for the accumulation dynamics along the trophic web also representing a source of pollution for the whole marine ecosystem.