Avaliação do nicho isotópico de peixes mesopredadores em recifes de corais alagoanos

Abstract

In light of current anthropogenic threats to different fish communities, it is necessary to evaluate the role played by these individuals in coral reefs. There is a positive relationship between the complexity of coral reefs and the species that use them. The complex structure of coral reefs can create a diverse ecosystem that offers varied resources. In addition to its socioeconomic importance for humans, it is a source of habitat, refuge, and protection for fish, invertebrates, and other organisms. The general objective of this study is to evaluate the isotopic niche of mesopredator fishes Cephalopholis fulva and Epinephelus adscensionis collected in different selected coral reefs in the Southwest Atlantic, in the municipalities of Maceió (Jatiúca and Ponta Verde) and Maragogi (Antunes, Galés, and Pedra do Meio). The specific objectives are to determine the amplitude of the isotopic niches used by the mesopredators studied and to compare the niches evaluated in the different types of management. 52 fish of the species E. adscensionis and 40 fish of the species C. fulva were collected. The specimens were taken to the laboratory, where they were stored for later analysis. The individuals had their weight and length measured and a portion of their muscle removed for isotopic niche analysis. The isotopic niche breadth of the species E. adscensionis and C. fulva showed relatively divergent results among the reefs analyzed. The broadest niche for the species E. adscensionis was in Maceió (1.57‰2 ), while the narrowest niche was in Galés (0.24‰2 ). For C. fulva, the broadest niche, however, was in Galés (1.37‰2 ) and the narrowest was in Ponta Verde (0.65‰2 ). The results for E. adscensionis indicate that the individuals that use the APACC reefs showed greater overlap than those from Maceió, which may suggest that these fish have a more similar diet among these reefs. The results from Jatiúca, however, imply that prey from lower trophic levels may have a difference in the proportion of δ 15N due to the greater availability of organic matter. C. fulva, on the other hand, overlapped in all reefs, which indicates a similar diet in each niche analyzed. Isotope analysis of δ 13C and δ 15N values revealed differences among the reef mesopredators studied, suggesting variations in the food sources of the species in the different niches used. These results indicate that the fish may be occupying and exploiting a wider range of food sources. In addition, the δ 13C and δ 15N signatures for the protected areas suggest that lower anthropogenic pressure, considering the results evaluated for niche breadth, allows the food chain of the different niches occupied to be more functional. The data evaluated reinforce the importance of studying mesopredators to understand their trophic dynamics and how they could influence conservation actions.