Placogorgia coronata first documented record in Italian waters: Use of trawl bycatch to unveil vulnerable deep-sea ecosystems

Despite the pluri-decennial history of bottom trawling monitoring in the Italian Sea, limited attention has been given to the study of cold water corals (CWCs) present in the bycatch. As a result, trawl samples still hold a great potential to reveal information about deep-water biodiversity. The rare Mediterranean CWC species Placogorgia coronata was repeatedly found in the bottom trawl discards of the red shrimp fishery in Santa Margherita Ligure (Ligurian Sea). The supposed rarity of this species is strongly biased by taxonomic problems within the genus as well as by the limited exploration of these deep habitats. Scientific literature as well as remotely operated vehicle surveys highlighted the presence, in the investigated trawled area, of a dead white coral framework, supporting the hypothesis that the CWC studied, probably thriving on coral rubble, occurs here due to the natural protection to trawling offered by the coral matrix. Trawlers, however, may accidentally affect these secondary hard grounds, as demonstrated by the discard content. The long-term monitoring of the catches highlighted a removal rate of up to one colony every two trawling operations; based on the anecdotal fishing effort in this area and the status of the discarded specimens, it is possible to estimate an average catch rate of about 18 live colonies per year per fisherman. The occurrence of rare CWC species with low resilience to fishing disturbance is among the required information for the identification of fishing restriction zones designed to protect deep vulnerable marine ecosystems.