Mangrove fish assemblages reflect the environmental diversity of the Galapagos Islands

Abstract

Mangroves are important habitats for a variety of ecologically, commercially and culturally important fishes. However, little is known about their role within the Tropical Eastern Pacific (TEP), and particularly in the Galapagos Archipelago, the westernmost limit for mangroves in the Americas, and the only oceanic islands in the TEP where mangroves are present. We describe patterns of fish composition in the 2 Galapagos bioregions where mangroves are present and assess potential environmental factors influencing fish community composition. Underwater Visual Census and Stereo Baited Remote Underwater Video stations (stereo-BRUVS) were used to sample fish communities. We identified 35029 fish representing 93 species, 67 genera and 36 families. Pomacentridae, Mugilidae, Haemulidae and Lutjanidae were the most common families. Juveniles made up 43% of the fish, 30 species were of importance to local artisanal fisheries and 80% of species were associated with reef habitats, suggesting mangroves in Galapagos may provide nursery habitats for economically valued species. Fish assemblage composition varied across bioregions, with 6 taxa responsible for driving these differences, including species of economic importance:Lutjanus novemfasciatusandMycteroperca olfax. Species richness was 17% higher in the Central-Southeastern than in the Western region; while higher species richness, Shannon-Wiener diversity and Pielou’s evenness were detected with BRUVS than through visual censuses. Our results highlight the role of mangroves as a habitat for a unique fish community composed of young, endemic and commercially important species, whose composition is likely driven by the isolation of the islands and its location in a convergence zone.