The impact of macroalgae and cyanobacteria on larval survival and settlement of the scleractinian corals Acropora palmata, A. cervicornis and Pseudodiploria strigosa

Coral reefs are threatened by multiple stressors that degrade these ecosystems and the ecosystem services they provide. Critical to the recovery of coral reefs after a disturbance is coral recruitment, but there is still little information about the types of benthic habitats that different species of coral larvae require for settlement. Settlement in the presence of different algae and cyanobacteria was tested for three coral species, Acropora palmata, Acropora cervicornis and Pseudodiploria strigosa. The experiments were conducted in larval chambers placed on the reef to ensure that coral larvae were exposed to natural light, seawater temperature and some water flow. Rates of settlement and metamorphosis were assessed by providing these coral larvae with a standard preferred settlement substratum (individuals of the crustose coralline algal species Hydrolithon boergesenii) with an attached treatment of a small piece of live algae or benthic cyanobacteria. The brown algae Dictyota pulchella and D. bartayresiana did not affect the survival or settlement of larvae of A. palmata in 2010, but D. pulchella did reduce larval survival in 2009. Of the cyanobacteria tested, Caldora penicillata decreased A. palmata survival and settlement. For A. cervicornis, neither Dictyota pulchella nor D. bartayresiana reduced survival or settlement in either 2009 or 2010. Algae and cyanobacteria had no effect on Pseudodiploria strigosa larval survival, but there was reduced settlement in the presence of the cyanobacterium Hormothamnion enteromorphoides. These larval experiments show that some macrophytes can reduce coral larval survival and settlement even in the presence of highly preferred substrata.