Subtidal benthic assemblages in a mediterranean bank along a depth gradient: Conservation perspectives of a vulnerable marine ecosystem

Abstract

Banks are ecologically relevant seafloor structures recognized as biodiversity hotspots, covering a wide range of depths in several geological contexts and encompassing heterogeneous habitat types and benthic assemblages. They support vulnerable species and habitats of conservation interest, including coralligenous outcrops that are well known as nursery areas for several species, including commercial fish species, and as carbon-flow regulating regions. The vulnerability of this habitat, characterized by species with slow growth rates, long recovery periods and exposed to multiple anthropogenic pressures, makes the implementation of appropriate conservation and management measures an urgent priority. The present work aimed to investigate: the diversity and patterns of distribution of this benthic habitat, with a focus on habitat-forming species, together with the abundance and composition of benthic litter of a protected Mediterranean bank at several depth ranges. Overall, ROV video analyses highlighted the presence of 73 taxa, including species of high biological interest protected by international conventions, and provided evidence of the presence of invasive species in the investigated bank, such as the native polychaete Hermodice carunculata and the non-indigenous seaweed Caulerpa cylindracea. Coralligenous outcrops are impacted by anthropogenic marine litter, confirming the exploitation of the bank as a fishing area. All marine litter was represented by artificial polymer materials, consisting of Abandoned, Lost or otherwise Discarded Fishing Gears (ALDFGs). The contextual high abundance of ALDFGs and the low abundance of erect habitat-forming species observed in the deep waters document a long history of mechanical disturbance caused by both operating and lost demersal fishing gears. This study represents an integrative baseline of information for the implemented Special Area of Conservation (SAC) “Secca di Amendolara” and the recently instituted homonymous regional marine park, showing the importance of fine scale data to support management measures aimed at increasing the effectiveness of ongoing conservation plans.