Island biogeography and marine fish diversity of oceanic islands

Abstract

Oceanic Islands have contributed significantly to our understanding of basic ecological and evolutionary processes, but most empirical data stem from terrestrial ecosystems. Does Island Biogeography theory explain marine diversity of oceanic islands? Here, we looked at how the island degree of isolation, size, human population, sea surface temperature, and degree of protection correlate with fish diversity and abundance. We used visual underwater census as specified by the Reef Life Survey Program to quantify the abundance and size of every fish species in 450 transects distributed over 26 tropical and temperate oceanic islands in the Atlantic, West Pacific, East Pacific, and the Tasman Sea. We used distance-based linear models to identify environmental variables that explained differences in fish populations. We also used data at the species, family, and trophic group level to test for differences in the organization of fish communities between geographic regions and islands beyond the expected differences in species composition. We found a strong and inverse relationship between species richness and distance to the closest continent. Total fish abundance was unrelated to distance to the closest continent or island size but negatively associated with human population. Dissimilarities in fish communities surpassed the expected differences in species composition between regions and were significant even at the trophic level of organization. These differences suggest not only taxonomical but functional differences in marine ecosystems at local and geographic scales. Despite these differences, Island Biogeography theory and human population can explain broad patterns of fish diversity and abundance. The impact of human population on marine systems could distort our understanding of the factors shaping marine biodiversity. Global approaches of the type presented in this study will help unravel natural and anthropogenic effects on marine biodiversity and contribute to his preservation.