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

Niche construction is the process through which organisms modify environmental states in ways favourable to their own fitness. Here, we test experimentally whether scleractinian corals can be considered niche constructors. In particular, we demonstrate a positive feedback involved in corals building structures which facilitate recruitment, a key process for coral reef persistence. Larvae require low flow conditions to settle from the plankton, so the presence of colony structures that can break the flow is expected to facilitate coral recruitment. Here, we show an increase in settler presence on artificial tiles deployed in the field along 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. This result provides evidence that coral built structural complexity creates conditions that facilitate coral settlement, therefore demonstrating that corals meet the criteria for ecological niche construction.