Comparison of sampling methods to assess marine benthic communities: visual vs destructive methods

Abstract

During the last decades, great efforts have been made to study the diversity and the degree of heterogeneity of Antarctic benthic communities. Numerous investigations on macrobenthic communities have recently been carried out at different sites in Antactic Peninsula using both visual and destructive methods covering a wide latitudinal range. In the present study, we compare the performance of two sampling gears by assessing quantitative data obtained by Agassiz trawls (AGT) and seabed images collected by the Ocean Floor Observation System (OFOS) on the continental shelf of three oceanographically very distinct regions: the Weddell Sea, the Bransfield Strait, and the Drake Passage to provide new quantitative data on the combination of different sampling methods on Antarctic megabethos. A total of 4213 individuals were sampled with AGT and 10550 individuals with OFOS. Combining AGT and OFOS data, we found a total of 19 benthic taxonomic groups. The most dominant groups sampled with AGT were Polychaeta and Ophiuroidea, while Ophiuroidea and Ascidiacea were for OFOS. Ophiuroidea was the most abundant group representing 45% of the individuals in OFOS and 19,1% in AGT. The extremely high abundance of all the taxa observed by OFOS with respect to the abundance estimated with AGT provides important insights into the efficiency of trawl gears in the study of benthic communities. Despite considering the benthic fractions in different resolution but with similar distribution patterns, nondestructive monitoring with visual techniques is extensively recommended for the proper study of Antarctic benthic communities and their consequent management