REPORT Can benthic algae mediate larval behavior and settlement of the coral Acropora muricata? V. Denis • M. Loubeyres • S. S. Doo • S. de Palmas • S. Keshavmurthy • H. J. Hsieh • C. A. Chen Received: 3 May 2013 / Accepted: 24 January 2014 Ó Springer-Verlag Berlin Heidelberg 2014 Abstract 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 aus- tralis (PA), and one crustose coralline algae, Mesophyllum simulans (MS), affects the settlement of Acropora muri- cata 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 oxy- gen, 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 sub- strate 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 microen- vironments by algae and their associated microbial com- munities 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. Keywords Mesophyllum Á Padina Á Sargassum Á Coral larvae Á Coral–algal interactions Á Reef recovery Introduction In synergy with local factors, rising seawater temperatures and ocean acidification may seriously affect the growth and survival of calcifying organisms such as corals and crustose coralline algae (CCA) (Hoegh-Guldberg et al. 2007). The widespread degradation of coral reef ecosystems today is undeniable, and reversing this trend seems to be an unprecedented challenge for the coming century (ICRS 2012). Yet, many reefs around the world have shifted from coral to algal (or other alternative taxa)-dominated Communicated by Biology Editor Dr. Mark Vermeij V. Denis and M. Loubeyres have contributed equally to this work. Electronic supplementary material The online version of this article (doi:10.1007/s00338-014-1127-4) contains supplementary material, which is available to authorized users. V. Denis Á M. Loubeyres Á S. S. Doo Á S. de Palmas Á S. Keshavmurthy Á C. A. Chen (&) Biodiversity Research Center, Academia Sinica, Nangang, Taipei 115, Taiwan e-mail: cac@gate.sinica.edu.tw Present Address: S. S. Doo School of Biological Sciences, University of Sydney, Sydney, Australia H. J. Hsieh Penghu Marine Biological Research Center, Makong, Taiwan C. A. Chen Taiwan International Graduate Program-Biodiversity, Academia Sinica, Nangang, Taipei 115, Taiwan C. A. Chen Institute of Oceanography, National Taiwan University, Taipei 106, Taiwan 123 Coral Reefs DOI 10.1007/s00338-014-1127-4