Coralline algae disease reduces survival and settlement success of coral planulae in laboratory experiments

Disease outbreaks have been involved in the deterioration of coral reefs worldwide and have been particularly striking among crustose coralline algae (CCA). Although CCA represent important cues for coral settlement, the impact of CCA diseases on the survival and settlement of coral planulae is unknown. Exposing coral larvae to healthy, diseased, and recently dead crusts from three important CCA species, we show a negative effect of disease in the inductive CCA species Hydrolithon boergesenii on larval survivorship of Orbicella faveolata and settlement of O. faveolata and Diploria labyrinthiformis on the CCA surface. No effect was found with the less inductive CCA species Neogoniolithon mamillare and Paragoniolithon accretum. Additionally, a majority of planulae that settled on top of diseased H. boergesenii crusts were on healthy rather than diseased/dying tissue. Our experiments suggest that CCA diseases have the potential to reduce the survivorship and settlement of coral planulae on coral reefs.