Diet and trophic position of three common rocky reef fish at two locations in the Gulf of California

Abstract

This study analyzed the spatial variation of stable isotopes (δ15N and δ13C) and the trophic position of three rocky reef fishes, Balistes polylepis, Stegastes rectifraenum and Kyphosus vaigiensis. According to previous feeding studies, these species are categorized as a benthic carnivore, an omnivore, and an herbivore, respectively. Specimens were sampled in two locations on the western Gulf of California: Bahía de La Paz and Santa Rosalía. For δ15N, the mean value recorded in S. rectifraenum was 18.1‰, followed by B. polylepis (17.7‰), and K. vaigiensis (16.7‰): omnivore–carnivore–herbivore. The mean δ13C value recorded for K. vaigiensis was –13.6‰, followed by S. rectifraenum (–14.9%) and B. polylepis (–16.1‰): herbivore–omnivore–carnivore.​ δ15N and δ13C values differed significantly between locations, except for δ15N for K. vaigiensis and δ13C for S. rectifraenum. Differences in δ15N may probably be related to oceanographic differences in productivity between the areas or to discharges of anthropogenic compounds. In general, the differences in δ13C between La Paz and Santa Rosalía suggest that fishes have different feeding grounds in each of the locations studied. The mean trophic position, estimated from both isotopes, varied between 2.91 in K. vaigiensis and 3.65 in S. rectifraenum. In La Paz, the isotopic niches of the three species overlapped, while in Santa Rosalía this overlap was observed only between B. polylepis and S. rectifraenum. This study is one of the first to apply stable isotopes as a tool to depict the trophic structure of the diverse biota associated with rocky reefs in the Gulf of California.