Otolith size trends in marine fish communities from different depth strata

A comparison of 681 saccular otoliths (sagitta) from 134 species belonging to six demersal communities from different depth strata and the epipelagic community from the north-western Mediterranean Sea was made in order to study otolith relative size and function related morphologies. A relationship between otolith size composition, habitat and depth was found. The epipelagic community was characterized by species with very small and small otolith sizes (68% of the epipelagic species). In the demersal communities, the proportion of species with large sagitta increased with depth until 750 m (reached 50% of the species of the upper slope). The abyssal community (between 1000 and 2000 m), however, was characterized by a decrease in the mean otolith size and an increase in the proportion of species with very small otoliths. With exception of the abyssal community, endogenous causes (a mixture of geneaology, plesiomorph characters shared by the all species of the taxonomic group and recent adaptive ones) may be even more important than exogenous factors in determining the otolith relative size. Within the endogenous causes that condition sagitta size, the adaptive features associated with specialization in acoustic communication are relevant.