The bottom morphology, the surface sediments and the epibenthic community of two adjacent areas
within the fishing ground traditionally known as Pesquera Rica (Balearic Islands) were characterized using
multibeam echosounder, van Veen dredge and beam trawl. Red algae beds predominate in both areas,
but one has been exploited by trawling since at least 90 years ago, whereas the presence of natural
barriers prevents this fishing activity in the other one. Comparisons between the two areas showed
a biomass reduction of 46.8 and 39.3% of dominant red algae taxonomic groups Peyssonneliaceae and
Corallinophycidae, respectively, in the trawled area (TA). Similarly, both mean abundance and biomass
of most groups of fauna were higher in the not trawled area (NTA). N90 biodiversity index showed higher
mean values of algae species in NTA than in TA (7.0 and 4.9, respectively), whereas no differences were
detected neither for sessile nor for mobile fauna. SIMPER analysis showed that large species of both
sessile and mobile epibenthic fauna (e.g. the ascidia Polycarpa mamillaris and the echinoderm Spatangus
purpureus, respectively) presented higher abundance and contribution to within area similarity in NTA
than in TA. In coincidence, these are the most abundant epibenthic species in the commercial hauls from
the Pesquera Rica. The relatively low fishing effort and the gears used, addressed to avoid large catches of
algae allowing longer hauls, may explain the subsistence of red algae beds in the Balearic Islands trawl
fishing grounds. However, the detrimental effects shown here claim for urgent management measures
aiming to preserve these beds
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