Effects of small-scale trawling on benthic communities of estuarine vegetated and non-vegetated habitats

Abstract

The pink prawn Farfantepenaeus paulensis is one of the most valuable fishery resources in the southwest Atlantic. It is exploited along the inner shelf and inside estuarine nursery grounds. Inside the nursery grounds, mainly artisanal fisheries are responsible for the capture of pink prawn juveniles. In this study, we experimentally assessed the impact of a light mini trawl, a gear extensively used for the capture of estuarine prawn along the southeast and south coast of Brazil. We simulated a single impact (represented by three consecutive trawling runs) on vegetated and non-vegetated bottom. Then we monitored changes in sediment properties and the response of the benthic fauna at the trawling and control sites at a logarithmic temporal scale in order to determine the initial impact and the recovery rates. Meiofauna and macrofauna, both numerically dominated by the ostracod Cyprideis multidentata, were significantly more diverse and abundant inside the submerged algal beds than in non-vegetated areas. In the vegetated areas, the only change caused by the mini trawl was a significant decrease in the percentages of fine sediments (silt+clay). By contrast, in the non-vegetated areas, the mini trawl caused a significant decrease of the total meiofauna, mainly due to lower nematode and C. multidentata abundances. Our results show that the mini trawl does not produce a loss of benthic diversity and causes minimal damage to the estuarine benthos. The absence of a general faunal response, as well as the absence of significant changes in sediment properties of the non-vegetated areas suggests that meiofauna may be resuspended rather than killed during trawling. The present study highlights the need for basic studies on gear impact and environmental health of nursery grounds. Otherwise, management of small-scale fisheries will continue to be based on evidence from large-scale fisheries.