Reef fish communities have been intensely studied on large reef systems in the Caribbean Sea and Western Pacific regions, whereas communities on small and remote oceanic islands are still poorly understood. Logistical constraints imposed by remoteness limit fieldwork time and increase research costs. However, since environmental impacts on these previously pristine localities are increasing, there is an urgent need to learn how these isolated communities are structured. Isolated islands have been long known as natural laboratories for ecology and evolution because they are ecologically simpler than larger continental habitats. In a study published this week, Osmar Luiz, Diego Barneche and their colleagues take the ecological simplicity of islands to the extreme by investigating the factors affecting the reef fish community of the smallest remote tropical island in the world: the St. Peter and St. Paul’s Archipelago in the equatorial Atlantic Ocean, on the mid-Atlantic ridge. The archipelago is only 400m across at its greatest extent and has the most depauperate reef fish assemblage known for a single tropical island, with roughly 60 species recorded. Ecological communities are often structured by a complex combination of abiotic and biotic factors. In the St. Peter and St. Paul’s Archipelago, however, none of the biotic variables studied appear to be important, probably because of less competition for resources due to low species richness and a large proportion of generalist species. On the other hand, depth was the most important driver of species abundance, biomass and diversity. The study finds that the island community is made up from functional groups that are represented by very few species—extremely low functional redundancy—and therefore highlights potential vulnerability to disturbances.
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