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Reef fish larvae visually discriminate coral diversity during settlement

To survive the pelagic stage, reef fish larvae need to find a settlement habitat and determine its suitability using a combination of environmental cues. Previous studies have shown that fish larvae are attracted by different components of their settlement habitat, such as conspecifics, algae, coral rubble, or living corals. However, it is not known whether larval fish use coral diversity as a settlement cue. Here, we tested the ability of presettlement reef fish larvae to discriminate coral diversity in laboratory experiments. We constructed coral assemblages of equal surface area, but with different coral species richness using live coral colonies of five species [Acropora cervicornis (Lamarck, 1816), Dichocoenia stokesii Milne-Edwards and Haime, 1848, Montastrea cavernosa (Linnaeus, 1767), Siderastrea siderea (Ellis and Solander, 1786), and Stephanocoenia intersepta (Lamarck, 1836)] and recorded the settlement choice of individual reef fish larvae. We found that reef fish larvae seem to prefer to settle on assemblages with higher coral diversity, regardless of the species used. We then used a two-choice tank to test the potential of reef fish larvae to visually perceive different coral species diversity and found that higher diversity attracts more settlement stage reef fish larvae, potentially changing the distribution of settlers at local scales. If preference for higher coral diversity stems from attraction to olfactory or other long-range cues—in addition to visual preference—coral diversity may play a role in connectivity among fish populations. This mechanism may further explain why degraded coral reefs do not maintain abundant fish populations.