Bottom trawling impact on benthic communitites of both maërl and muddy habitats: a case study in the Costa Brava (NW Mediterranean)

Abstract

Bottom trawling presents a negative impact on benthic communities, with a direct impact on caught species and an indirect impact on infaunal organisms. Research has shown that heavily trawled areas present lower diversity of species and are dominated by opportunistic infauna, as they present high resilience to trawling. This study aims to understand the impact of bottom trawling on benthic communities, analyzing both regulated and unregulated discards and infauna community. The study was developed in two different habitats, maërl and mud, located in two fishing grounds of Blanes, Capets and Garotes (NW Mediterranean Sea). Biomass and abundance of discarded fraction was analyzed, showing that Capets presented higher unregulated discards and Garotes higher regulated discards in both abundance and biomass. Abundance of infauna was also analyzed, showing that Annelida was the most abundant phylum in Capets, whereas in Garotes those were Annelida and Arthropoda. Furthermore, fishing effort and productivity (biomass and total income) of the two fishing grounds was also studied. Analysis of the species richness and biodiversity of both discarded species (regulated and unregulated) and infauna showed significant differences between the two fishing grounds, being higher in Garotes. Fishing seasonality showed a different level of effort due to the fishing ban, which was on February in Capets, whereas in Garotes it was from April to August. Diet of target species in both fishing grounds was studied comparing both invertebrate discarded fraction and infaunal organisms. The phyla Arthropoda and Mollusca that constituted mostly their diet were found in low abundance because of their vulnerability to trawling. Nevertheless, the opportunistic phylum Annelida was the most abundant and it was found on both fishing grounds. Although productivity in terms of economic value was higher in Capets, Garotes presented a higher ecological value because of its maërl bed. The results of this study pointed out the conservation importance of maërl beds in the Mediterranean. Thus, the creation of Marine Protected Areas (MPAs) in maërl beds of Garotes is proposed in order to avoid further degradation of this habitat. MPAs would increase the complexity of the ecosystems and the biomass of target species in Garotes, which would increase the income of fishers