Can benthic algae mediate larval behavior and settlement of the coral Acropora muricata?
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The resilience of coral reefs relies significantly on the ability of corals to recover successfully in algal-dominated environments. Larval settlement is a critical but highly vulnerable stage in the early life history of corals. In this study, we analyzed how the presence of two upright fleshy algae, Sargassum mcclurei (SM) and Padina australis (PA), and one crustose coralline algae, Mesophyllum simulans (MS), affects the settlement of Acropora muricata larvae. Coral larvae were exposed to seawater flowing over these algae at two concentrations. Larval settlement and mortality were assessed daily through four variables related to their behavior: swimming, substratum testing, metamorphosis, and stresses. Temperature, dissolved oxygen, pH, algal growth, and photosynthetic efficiency were monitored throughout the experiment. Results showed that A. muricata larvae can settle successfully in the absence of external stimuli (63 ± 6 % of the larvae settled in control treatments). While algae such as MS may stimulate substrate testing and settlement of larvae in the first day after competency, they ultimately had a lower settlement rate than controls. Fleshy algae such as PA, and in a lesser measure SM, induced more metamorphosis than controls and seemed to eventually stimulate settlement. A diverse combination of signals and/or modifications of microenvironments by algae and their associated microbial communities may explain the pattern observed in coral settlement. Overall, this study contributes significantly to the knowledge of the interaction between coral and algae, which is critical for the resilience of the reefs.
KeywordsMesophyllum Padina Sargassum Coral larvae Coral–algal interactions Reef recovery
We are grateful to the staff of the Penghu Marine Biological Research Center and members of the Coral Lab for helping us to perform this experiment. We also thank Dr. Yoko Nozawa and Julia Ka Lai Leung for their useful comments and advice on this manuscript and Michael Honeth for English editing. This work was supported by a grant from Academia Sinica (AS-100-TP2-A02-3). VD is the recipient of a postdoctoral fellowship from the National Science Council of Taiwan, ML and SSD of a grant from the Taiwan International Graduate Program, and SK by a postdoctoral fellowship from Academia Sinica. This is a contribution #88 of Coral Lab, Biodiversity Research Center, Academia Sinica.
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