Effects of bottom trawling on the benthic assemblages in the south Adriatic Sea (Montenegro)

Trawling remains a controversial method of fishing due to the perceived lack of selectivity of the trawl net, which can result in the capture of a huge quantity and diversity of non-target species, including endangered species, and have a significant effect on the marine ecosystem (KUMAR & DEEPTHI, 2006). Trawl fishing has both direct and indirect impacts on the marine ecosystem as well as on biodiversity, as it collects and kills a huge amount of non-target species and young individuals of commercially valuable species, mechanically disturbs the sea bottom, and injures a wide variety of marine benthic organisms (KNIEB, 1991). The environmental damage caused by bottom trawling can be substantial and irreversible (WATLING & NORSE, 1998). Trawling does not cause damage just to the physical attributes of the habitats, therefore implying a reduction in biodiversity, but can also cause changes to the benthic assemblage structure, species abundance, and their size structure (GARCÍA-RODRÍGUES et al., 2011). However, most of the disturbances at the sea bottom remain unrecorded as they are hidden from direct human The purpose of this study is to show the effects of bottom trawling on the benthic assemblages in the south Adriatic Sea as well as to report detailed quantitative and qualitative data on some invertebrate groups of no commercial value that are affected by trawling. Short-term effects of bottom trawling on the soft bottom seafloor were studied on the continental shelf and upper slope in the southeastern Adriatic Sea. Ten sites were trawled in July 2011. A total of 14,069 invertebrate organisms belonging to 44 taxa were collected within the study period. Of these, 93 were Sponges (4 species), 509 Cnidarians (7 species), 3,670 Molluscs (5 species), 48 Bryozoa (1 species), 3,154 Echinoderms (14 species), and 7,054 Tunicates (13 species). Cluster analysis performed with the data from different depth layers showed two clearly separated main groups that corresponded to shelf and slope zone. The shelf zone samples were characterized by higher species richness, while samples taken from the slope contained one species, Pteroeides spinosums. The obtained results showed that the most common species during the survey were Pteria hirundo, Ascidia virginea, Phallusia mammillata, Botryllus schlosseri, and Centrostephanus longispinus. Species P. mammillata, B. schlosseri, and P. regalis presented the highest value of biomass index (kg/km2). Our results showed that ascidians, cnidarians, and echinoderms are the most vulnerable taxa to trawling.