Diet and trophic level of scaldfish Arnoglossus laterna in the southern Tyrrhenian Sea (western Mediterranean): contrasting trawled versus untrawled areas

This study assesses the effects of bottom trawling on the feeding ecology of the scaldfish Arnoglossus laterna, by contrasting diets in an untrawled area and in two trawled areas off northern Sicily (western Mediterranean): the Gulf of Castellammare (which hosts a 200 km(2) no-trawl area) and the guns of Termini Imerese and Sant'Agata. Scaldfish were collected in May-June 2005 using a commercial otter trawler between 40 and 80 in on muddy bottoms. Our data show that scaldfish is a selective feeder and consumes similar prey items in the three gulfs, although between-site differences in the relative prey abundance in the stomachs were detected. In the three guns scaldfish fed mainly on the crab Goneplax rhomboides and on the fish Lesueurigobius suerii, but there was an increase in the consumption of L. suerii and the shrimp Alpheus glaber in the trawled areas. Ontogenetic changes were evident in the diet Of scaldfish, with juveniles preying mainly upon suprabenthic species, e.g. mysids and small decapods. While significant differences occurred in the diet of juveniles among all areas due to natural spatial variability, variations in the diet of adults, which feed on benthic prey, occurred between untrawled and trawled areas. These variations were clearly due to trawling disturbance, and no significant difference was detected in the diet of adults between the two trawled areas. On the contrary, the trophic level (delta N-15 values) of scaldfish did riot vary between trawled and untrawled areas and between juveniles and adults. Changes in the source of carbon, as detected by delta C-13 values, were evident between juveniles and adults, evidencing a shift from a suprabenthic (juveniles) to a benthic (adults) diet.