Small-scale habitat selection by larvae of a reef-building coral

When animals select habitats, they integrate positive and negative cues in the environment that shape their choices about where to live. We conducted a settlement experiment with the larvae of Orbicella faveolata, a reef-building scleractinian coral on Caribbean reefs. We investigated the settlement decisions of O. faveolata larvae in relation to communities of benthic spaceholders and explicitly investigated how benthic communities influence how larvae may make settlement decisions at small spatial scales. Settlement tiles that attracted at least one O. faveolata settler had a significantly different community composition than tiles with no settlers. Red filamentous algae and crustose coralline algae were abundant on tiles with no settlers, while bare substrate was abundant on tiles with settlers. When we analyzed the spatial patterns of coral settlement within tiles, coral settlers avoided areas with sediment, sponges, and red filamentous algae and preferred areas with green filamentous algae. Selection among individual taxa was dominated by selecting against rather than for taxa. Our results show that coral larvae make complex decisions about where to settle even down to the millimeter scale. Importantly, these coral larvae select their habitat by balancing contrasting forces to avoid risks.