Coral ecological niche construction: coral settlement increases along a coral-built structural complexity gradient

Niche construction is the process through which organisms modify environmental states in ways that bias their own fitness. Here, we test experimentally whether Scleractinian corals can be considered niche constructors. In particular, we demonstrate an ecological feedback involved in branching corals building structures which facilitate coral settlement, a key process for reef persistence. Larvae require low flow conditions to settle out from the plankton, so the presence of colony structures that can break the flow is expected to facilitate coral settlement. Here, we show an increase in settler presence on the surface of artificial tiles deployed in the field with coral fragments attached on the top surface, which built a gradient of coral-built structural complexity. Structural complexity had a positive effect on settlement, with an increase of more than 15% probability of settler presence along the range of structural complexity considered. However, whether the corals forming the structures were alive or dead did not have an effect across this range. This result provides evidence that coral-built structural complexity creates conditions that facilitate coral settlement, demonstrating that corals can meet the criteria for ecological niche construction.