Bioerosion by the sea urchin Echinometra mathaei modulates coral recruitment in Moorea, French Polynesia

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Bioerosion on coral reefs is generally accepted as a detrimental process favoring the loss of coral and weakening the calcareous framework.  However, it is possible that increasing topographic complexity resulting from erosion may facilitate coral recruitment.  In this study I tested the hypothesis that the echinoid Echinometra mathaei facilitates coral recruitment through the creation of habitat on massive Porites patchreefs in the backreef in Moorea. Over 4 months, the smallest fraction of juvenile Pocillopora spp. transplanted into grazing grooves where E. mathaei had been removed survived, whereas survival increased for corals transplanted into grooves with the sea urchin and was the greatest for corals transplanted onto open surfaces.  However, corals in grooves devoid of sea urchins increased in size more than those in grooves with sea urchins or on open surfaces. These differences are likely a consequence of variation in both juvenile Pocillopora growth rates and corallivory by sea urchins and fishes. Together, these results reveal potentially strong, yet indirect effects by sea urchins creating relief that later promotes coral success after grooves are vacated by sea urchins.