Almeida, C. Caracterization of the macro epifauna associated with sandy substrates off the Central Algarve

Between November 2003 and April 2004, benthic communities on soft-bottom were sampled off the Algarve coast, using a beam trawl and visual censuses. The study area, between Albufeira and Vale do Lobo, was stratified by depth and type of sediment. A total of 35988 individuals were collected and 300 taxa identified in the 128 trawls realised. Echinodermata was the most abundant phylum, mainly related to the high frequency of occurrence of species like Ophiura albida and Astropecten aranciacus. These organisms have low mortality rates when disturbed by fishing activities since they are more resistant and can also benefit from food availability. The lack of knowledge of this kind of habitat was revealed by the presence of some species not described before for the zone. Differences were found between depths of 0-10 m in comparison with 10-20 and 20-30 m intervals. However, the highest values of biomass and diversity were recorded at depths of 20-30 m. The low values found in the minor depths can be consequence of fishery activity or to the natural hydrodynamics. In terms of substratum the identified differences were just related with gravel, which may be due to a lack of precision in the classification of the type of sediment. The highest values of abundance and biomass were associated with the rock outcrop substratum. Although sampling did not take place over a whole year, highest values of biomass, abundance and diversity were recorded during the Winter. In terms of sampling method, the visual census was shown to be an adequate qualitative method while the beam trawl provided good quantitative estimates and can sample large areas. The high number of species identified and the representativity of the sampling make this study an important contribution for the biodiversity knowledge off the Algarve coast.