The effects of trawling on the benthic fauna of the Gulf of Nicoya, Costa Rica

Four van Veen grab replicates where collected to sample macrofauna (organism retained on a 500 micron mesh sieve) at four stations in the Gulf of Nicoya, during October 24, 1997, January 16 and April 30, 1998. This information was used to search for any effects of trawling on the benthic fauna. Two stations where located in a trawled area, and two stations where in a protected area. Diversity (H') varied from 2.01 to 3.52 in the trawled area and from 2.13 to 2.78 in the protected area. Diversity was generally higher in the trawled area, and this was in contradiction to what we would have expected from other studies where the trend has been that trawling reduces diversity. Brittlestars and lancelets seemed to be the groups mostly harmed by the trawling, while amphipods where more abundant in trawled areas. The multivariate analyses did not reveal the patterns of faunal change as well as we hoped. This is surely because of our lack of more replicate samples. The multivariate analyses are easily confounded when few sites are analyzed. We have found differences in the type of fauna found in trawled and protected areas and, considering the differences in environmental variables in our stations and our lack of replication, this indicates that there are differences and a larger investigation is in order to reveal its magnitude.