[A-CG40] Coastal Ecosystems 2. Coral reefs, seagrass and macroalgal beds, and mangroves

[ACG40-04] Warm temperate coral recruitment and planula larvae physiology under ocean acidification

*Agostini Sylvain¹, Marco Milazzo², Martina Salermo², Giacomo Milisenda^3,4, Ben P Harvey¹, Kazuo Inaba¹, Giovanni D'Anna³, Carlo Pipitone³, Ikuko Yuyama⁶, Tomihiko Higuchi⁵, Arturo Zenone³, Fabio Badalamenti³ (1.Shimoda Marine Research Center, University of Tsukuba, 2.Dipartimento di Scienze della Terra a del Mare, Università Di Palermo, Palermo, Italy, 3.CNR-IAS, Castellammare Del Golfo (TP), Italy, 4.Stazione Zoologica Anton Dohrn, Naples Italy, 5.Atmospheric and Ocean Research Institute, The University of Tokyo, 6.Yamaguchi University)

Keywords:ocean acidification, planula larvae, microrespiration, cue selection, settlement rate

Ocean acidification (OA) is a major threat to corals, also at high latitudes where tropical species are moving as a consequence of ocean warming. OA interferes with the carbonate system leading to unfavourable conditions for calcifying organisms, and boosting macroalgae- and turf-dominated communities. Here we investigated the effect of ocean acidification on the larval recruitment of two warm temperate species, the Mediterranean Astroides calycularis (Pallas, 1766) and the West-Pacific Alveopora japonica (Eguchi, 1968). We used an integrate approach where the direct and indirect effects of ocean acididication were investigated. We tested the potential direct effect of the planula larvae of these two species through the assessment of respiration rates, transcriptomic, swimming speed and cilia movement. As coral larvae typically respond positively to chemical cues originated by coral colonies and coralline algae, which are expected to decline under OA, and negatively to cues from macroalgae and turfs, we expect a less successful recruitment of coral larvae in an acidified ocean, which would consist in an indirect effect. Therefore, we have compared habitat selection and settlement of coral larvae in conditions of control and elevated CO₂. Cue selection experiments were run to assess the preference for different cues (positive: organisms sampled from control pH sites, and negative: organisms sampled from naturally acidified sites) under both CO₂ conditions (present concentration and elevated concentration). Settlement experiments using a fully cross factorial design – consisting of larvae exposed to control and low pH seawater and to early-stage biofilm substrata from ambient and low pH environments – were done to assess the recruitment success under future conditions of ocean acidification.