Trophic niche overlap between flatfishes in a nursery area on the Portuguese coast

The diets and the trophic niche overlap between seven flatfish species were studied in a coastal nursery adjoining to the Tagus estuary (Portugal). Fish were sampled monthly, from March to November 1999, using a beach seine. Arnoglossus imperialis (Rafinesque, 1810), Arnoglossus laterna (Walbaum, 1792) and Arnoglossus thori Kyle, 1913, fed mainly on crustaceans. The diets of Buglossidium luteum (Risso, 18 10) and Dicologoglossa cuneata (Moreau, 188 1) were mainly composed of Bivalvia and Polychaeta, while for Scophthalmus rhombus (Linnaeus, 1758) the main food items were Mysidacea and Teleostei. The diet of Pegusa lascaris (Risso, 18 10) was mainly composed by Cumacea, Bivalvia, Decapoda and Amphipoda. Based on diet similarities two main groups were identified: one composed of A, imperialis, A. laterna, A. thori and S. rhombus, and the other grouping B. luteum, P, lascaris and D. cuneata. For the most common flatfishes, a similar pattern of diet seasonal variation was found, such that Amphipoda presented higher indices values in the period from March to June, while from July to November, Decapoda were more abundant. Although high values of diet overlap were obtained among some of the species, the main items in the diet of flatfishes are probably the most abundant prey in this coastal area, which suggests a generalist and opportunistic utilization of these food resources, Furthermore, niche overlap between these species is probably minimized by differences in resource use in other niche dimensions, namely time and space.