Feeding of the deep-water fish Helicolenus dactylopterus (Delaroche, 1809) in different habitats: from muddy bottoms to cold-water coral habitats

The present study represents the first documentation of the trophic spectrum of the deep-water teleost fish Helicolenus dactylopterus in two basins of the central Mediterranean (Northern Ionian and Southern Adriatic) and the first attempt to compare the diets of this deep-water teleost fish between two different habitats: flat muddy seabed and cold-water coral (CWC) habitat. 346 stomachs were collected on muddy bottoms and 352 in CWC habitats. The feeding habit of H. dactylopterus in the two investigated habitats was different. The vacuity index was higher in CWC habitats than on muddy bottoms, while a lower number of prey categories were shown in the former (22) than in the latter (63). Crustaceans were the most important prey in the diet of the specimens found on the muddy bottoms (%PSIRI = 61.16), while teleosts were the most abundant in CWC habitats (%PSIRI = 64.58). Ontogenetic dietary variation was evident only on soft bottoms with crustaceans as the most important portion of the diet in smaller specimens and with an increase in the consumption of fish with increasing size. The comparison of the diet between the two different study habitats was carried out considering two samples of specimens with overlapping sizes. Dietary differences were significant as shown both by Morisita's index and PERMANOVA. Considering that the effect of the tool on the diet, as proved, could be excluded, the blackbelly rosefish shows a different diet depending on the habitat in which it lives. The trophic niche breadth showed how H. dactylopterus was more generalist on muddy bottoms (Bi = 0.50) and more specialist in CWC habitats (Bi = 0.15). The trophic level was found to be higher in CWC habitats than on muddy bottoms.