Reef fish functional composition and metrics reveal spatial differences in three protected islands in the Eastern Pacific

Reef fish assemblages in the Eastern Pacific (EP) represent an interesting system to understand how areas with lower diversity respond to multiple factors and their effect on ecosystem functions and services. Among the multiple approaches that have emerged, the evaluation of functional metrics provides an initial comprehension of these relationships. In this context, to better understand reef fish variability in the EP, we evaluated spatial differences in ecological metrics, the composition of fish assemblages, and their relationship with habitat structure in coral communities at 3 islands in Mexico (Marietas, Isabel, and Cleofas). To include a functional approach, we created a functional entity (FE) matrix using species abundance and 6 categorical functional traits; specifically, we calculated ecological metrics that reflect the representation or under-representation of species in the functions or FEs (redundancy and vulnerability) and the rarity in FEs and species and their relationship with habitat structure. Overall, most of the fish FEs in the EP were represented by 1 species (i.e. high vulnerability and low functional redundancy). Despite the low redundancy recorded in the islands, reef fish performed multiple key functions; however, many functions remained rare. Furthermore, both metrics and fish composition showed high variability among sites and islands, but this variability was only partially explained by a few variables of habitat structure (i.e. rugosity). These results, in combination with the unique characteristics of coral communities in the EP, highlight the need to identify the drivers of fish assemblages and their effect on the ecosystem processes and services in order to implement unique management strategies for each island.