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Importance of Shellfish in the Diet of Two Ray Species (Rhinoptera steindachneri and Hypanus dipterurus) in the Upper Gulf of California

ABSTRACT The upper Gulf of California, Mexico is a marine protected area (MPA), considered important for the conservation and protection of species. The present study assessed the resource–consumer interactions of two ray species (Rhinoptera steindachneri and Hypanus dipterurus), to know the importance of shellfish in the food-web dynamics of two predators present in this MPA. A total of 33 prey species for R. steindachneri and 48 prey species for H. dipterurus were recorded. The bivalve Tellina subtrigona (%IRI = 99.5) was the most important species in the diet of R. steindachneri; whereas the gastropod Mitrella dorma (%IRI = 32.7) was the primary prey of H. dipterurus. The ray R. steindachneri had a lower Shannon's index of diversity (H' = 0.49) than H. dipterurus (H' = 1.41). Based on Amundsen's graphical method, R. steindachneri have a specialist feeding strategy; whereas H. dipterurus presented a mixed strategy that includes both specialist and generalist organisms. However, the trophic specialization evidenced by these rays may reflect the grouping behavior of their prey, which tend to form large aggregations. Both ray species are secondary consumers (TLR. steindachneri = 3.10 and TL H. dipterurus = 3.12) of shellfish. Nevertheless, there is a low similarity in the prey species composition between them (ANOSIM: R = 0.47), indicating that these two ray species have different diets, and therefore, each ray species has specific resource–consumer interactions. This information allows to understand the importance of shellfish in the food-web dynamics in the ecosystem and MPA effectiveness in the upper Gulf of California for species at risk, like ray species.