An experimental evaluation of the short-term effects of trawling on infaunal assemblages of the coast off southern Brazil

Bottom trawling is a large-scale fishing activity along the Brazilian coast, but its effects on benthic infauna are still poorly known. This is the first experimental evaluation of benthic responses to bottom trawling along the Brazilian coast. We tested the effects of trawling on macroinfaunal assemblages on the inner continental shelf off Parana (southern Brazil) by using a sampling design with adjacent trawl and control areas. We hypothesized that if trawl fishing has a negative effect then we should expect lower numbers of species and lower benthic densities after an experimental trawling. Sampling was conducted at adjacent sites within each area to minimize confounding due to spatial variation. Five sites were sampled at a control, and five at an experimental area for infaunal and sedimentological variables. Sampling was carried out just before and one hour after experimental trawling. Multidimensional scaling followed by a PERMANOVA did not show any clear variation tendencies in the structure of the benthic assemblages in the impacted area before and after trawling. However, variance analysis showed a significant and unexpected increase in infaunal total density, in the density of the numerically dominant species (except for the polychaetes Capitella sp. and Loandalia tricuspis) and in species richness in the experimental area. Conversely, no significant variations were recorded in the control area. We suggest that the overall increase in benthic density after a disturbance is correlated with the reworking of the sediment matrix and benefits the suspension-feeders after sediment resuspension.