High CO2 inhibits substratum exploration and settlement of coral larvae
Résumé
Biological and physical factors affecting coral recruitment are critical in influencing the recovery of coral communities after disturbance. While ocean acidification (OA) can reduce coral settlement and the early growth of coral recruits, the impact of OA on coral larval swimming behavior is unknown. Here, we investigated the effects of elevated CO 2 on the swimming behavior and settlement of coral larvae of 2 common Acropora species. Larvae were exposed to 4 CO 2 partial pressure ( p CO 2 ) conditions consistent with the current Intergovernmental Panel for Climate Change predictions for the next few centuries ( p CO 2 : 393, 853, 1485 and 3022 µatm; pH: 8.1, 7.8, 7.6 and 7.3) in 2 laboratory experiments. We found that bottom exploration, expressed as the proportion of A. cytherea and A. pulchra larvae present in the bottom part of experimental cylinders, decreased by 92 and 98%, respectively, from the ambient to highest CO 2 treatment. When offered the choice to settle on the crustose coralline algae Titanoderma prototypum , a well-known positive settlement cue, the percentage of larvae that settled on the fragments declined rapidly as p CO 2 increased, with no larvae settling in the highest CO 2 treatment. These results suggest that OA may negatively affect coral recruitment via direct effects on larval swimming behavior, with larvae avoiding benthic probing in response to high CO 2 .