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

Abstract

1 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.2 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.3 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.4 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.5 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.

Megabenthic communities of the Ligurian deep continental shelf and shelf break (NW Mediterranean Sea)

“…The deep-sea megafauna (>200 m) has also been partially characterized, mainly through a long history of scientific observations of the trawling discards [16,17,18,19]. Indeed, the cold-water coral banks located along the Ligurian continental slope, and recorded in the fishing bycatch, were already tentatively mapped by Fusco in 1968 [20,21].…”

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

“…In contrast, the information regarding small‐sized gorgonian assemblages is much more scant because of difficulties with the identification of taxa (Chimienti et al, 2019). Numerous species studied here have been reported in Mediterranean canyons and on seamounts (Aguilar et al, 2013; De la Torriente et al, 2018; Deidun et al, 2015; Enrichetti et al, 2018; Evans et al, 2016; Hebbeln et al, 2009; López‐González & Cunha, 2010), but the Muriceides / Villogorgia assemblages found on the Ulisse and Penelope seamounts are among the densest and richest in terms of associated fauna. This is also supported by the fact that the preferential habitat of these gorgonians in the studied area is the dead coral framework, which is known for providing secondary substrate and refuge to many species (Rueda et al, 2019).…”

“…The evidence presented in this study gives a qualitative understanding of what, in the early 1970s, could have been regarded as a pristine deep refuge in an otherwise already highly exploited basin (Enrichetti et al, 2018, 2019; Relini et al, 1986). Catch data between 1973 and 1975 support the existence of a population of at least 120 Polyprion americanus living in a territory of approximately 12 km 2 , corresponding to the area of the two rocky summits.…”

“…The Ulisse and Penelope seamounts are two of the most exploited deep geological reliefs of the north‐western Ligurian Sea (Würtz & Rovere, 2015). From the biological perspective, there are various reasons supporting the great interest in surveying these two seamounts, particularly their bathyal location, which is poorly explored in the Liguro‐Provençal basin, the coldest region of the western Mediterranean basin (Bo et al, 2020; Enrichetti, Bavestrello, Coppari, Betti, & Bo, 2018; Fanelli et al, 2017; Relini, Peirano, & Tunesi, 1986; Rossi, 1958; Sartoretto & Zibrowius, 2018). Furthermore, from the perspective of conservation, the high levels of exploitation of these areas by fishermen offer the opportunity to evaluate the short‐ and long‐term (about 50 years) effects of the removal of large fishes and mechanical disturbance on cold‐water habitat‐forming corals.…”

“…The Ulisse and Penelope seamounts are part of a common volcanic edifice and are close enough to each other (6 km) to share approximately 70% of the reported species. Many taxa are also shared with nearby continental slope ecosystems at similar bathyal depths, particularly the continental and Corse French canyons (Boury‐Esnault et al, 2017; Fabri et al, 2014; Fabri, Pedel, & Madurell, 2012) and the Italian canyons (Enrichetti et al, 2018; Giusti et al, 2019). This suggests a certain degree of connectivity among similar ecosystems within the same biogeographic context, as previously observed in other studies, and supports the lack of high endemicity levels traditionally attributed to isolated seamounts (Clark et al, 2010; Howell, Mowles, & Foggo, 2010; McClain, 2007; Rowden et al, 2010; Schlacher, Rowden, Dower, & Consalvey, 2010).…”