Ontogenetic diet shifts and food partitioning between two small sympatric skates (Chondrichthyes, Rajidae) in the Southwestern Atlantic

Abstract

Knowing how sympatric species partition their resources is very important for understanding the mechanisms that influence marine community structure. We test the hypothesis of resource partitioning between two sympatric, closely related, morphologically similar, small skates, Psammobatis bergi and P. extenta. The diets of the two species were different. P. bergi fed predominantly on crabs, amphipods, isopods and polychaetes. P. extenta consumed mainly amphipods and shrimps. Changes in the diet with body size, maturity stage and season varied among species. The consumption of amphipods decreased with increasing size of both species. The consumption of crabs increased with increasing size of P. bergi, but decreased with increasing size of P. extenta. The consumption of cumaceans increased with size of P. extenta and decreased with size of P. bergi. Adults preyed on isopods more heavily than juveniles for both species. P. extenta preyed on shrimps more heavily in the warm season and, on the contrary P. bergi preyed on shrimps more often in the cold season. The dietary breadth was higher in P. bergi than in P. extenta and was higher in females than in males. Our results showed that these sympatric and closely-related species have clearly different trophic traits.