Deep-sea suprabenthic assemblages in the Blanes canyon and adjacent open slope (NW Mediterranean): diversity and spatio-temporal variations in important fishing grounds

Abstract

The multidisciplinary RECS project aimed to study the benthic communities in the Blanes canyon (Northwestern Mediterranean Sea). The lower depths of the canyon and adjacent areas are exploited by fisheries for the red shrimp Aristeus antennatus. In this context, the macrofauna living in the vicinity of the bottom (suprabenthos) was sampled in order to study diversity and distribution patterns in the canyon and open slope in relation to environmental variables and fishing pressure. This fauna is composed by mobile animals (small crustaceans) that perform daily or seasonal migrations and are known to be source of food for megafauna species, including those with commercial value. Sampling was conducted seasonally (March 2003-May 2004) in fishing and non-fishing areas in the open slope (at approx. 800m) and inside the canyon in two areas trawled for fisheries (at approx. at 500m). The samples were sorted and identified to the lower taxonomic level, counted and weighed. Biodiversity, densities and biomasses were estimated between canyon and open slope and between fished and non-fished areas. Trophic structure and life styles were also compared. Considering the fishing areas, preliminary results indicate higher diversity and evenness in open slope assemblages and higher dominance and densities in the canyon assemblages. The multivariate analysis supports a significant difference between canyon and open slope stations. For the analysis between fished and non-fished areas, even so the multivariate analyses did not detected significant differences between the two areas, lower densities and higher diversity was found in the open slope stations impacted by trawling. The analysis is not completed yet, even so the preliminary results indicate that there is a “canyon effect” on suprabenthos and fishing pressure could be an additional factor structuring these communities