The high biodiversity and vulnerability of two Mediterranean bathyal seamounts support the need for creating offshore protected areas

Seamounts host some of the most important deep-sea ecosystems. The unique environmental characteristics of seamounts sustain rich biological hot spots, which, in recent times, have suffered the effects of intense fishing pressure. Biodiversity and vulnerability data are extremely scarce for Mediterranean seamounts, and this, in addition to the complex socio-economic and juridical status of offshore sites, results in difficulty in identifying the best management strategies. An extensive remotely operated vehicle (ROV) survey was used to characterize the megabenthic assemblages of the summits of two upper bathyal seamounts, Ulisse and Penelope (Ligurian Sea, north-west Mediterranean Sea). The biogeographic implications of these findings and the possible environmental factors favouring the occurrence of these communities are discussed. High densities of abandoned, lost, or otherwise discarded fishing gear (mainly longlines) and a reduction in the average size of the fragile and slow-growing habitat-forming gorgonian Callogorgia verticillata indicate the occurrence of high levels of anthropogenic impacts on the summit regions, which are fishing grounds for artisanal and recreational fishers. The recovery of fishing data describing the first catches in the 1970s proved to be useful in inferring the short- and long-term effects of fishing practices in these previously unexploited offshore areas. In particular, the local extinction of demersal top predators, subjected to exceptional catches nearly 50 years ago, highlights the slow recovery rate of such species. Criteria defining vulnerability are discussed for the two study areas, and specific conservation actions, including the creation of regulated protected areas, are proposed.