Benthic diversity in the Patagonian scallop fishing grounds along the Argentine shelf-break front, Southwestern Atlantic Ocean

The study of the benthic community associated with the Patagonian scallop fishery (Zygochlamys patagonica) has been carried out periodically by the Benthic Mollusc Fisheries Programme (INIDEP) since the fishery began in 1996. The objective of this study was to provide comparative information on the richness, diversity and biomass of the benthic invertebrate community in two of the main Patagonian scallop fishing grounds (FG_D and FG_E) in Argentina during the period between 2015 and 2022. The study area covers soft bottoms between 41°25'S and 43°02'S. Depths range from 87 to 131 m in the SW Atlantic Ocean. A total of 254 samples were studied from five stock assessment cruises using a non-selective dredge. Each sample analysed consisted of approximately 10 litres of unsorted catch. A total of 90 taxa were recorded in the area. FG_D had a higher biomass of benthic communities and associated fauna than FG_E. Porifera was dominant in FG_D, whereas Ophiuroidea was dominant in FG_E. In addition, the specific richness was significantly higher in FG_D. The asymptotic specific richness was 98 species in FG_D and 74 species in FG_E. The observed and estimated effective numbers of common and dominant species were similar in both FGs. The most conspicuous association of species was formed by the Patagonian scallop Z. patagonica, the brittle stars Ophiosabine vivipara, Ophiactis asperula and Ophiuroglypha lymani, Porifera, the sea urchin Sterechinus agassizii and the cnidarian Alcyonium sp. Although this association showed some differences between years, these were related to variations in the biomass contribution of the main species to the total community. The composition of the benthic community and the species association did not differ from those previously recorded for these FGs in previous years.