Hong Kong Coral Recruits Do Not Gain Advantage by being Flexible in Establishing Symbiosis under Simulated Climate Change Conditions

Ng, T.Y.; Chui, A.P.Y.; Tsang, R.H.L.; Yeung, C.W., and Ang, P., 2024. Hong Kong coral recruits do not gain advantage by being flexible in establishing symbiosis under simulated climate change conditions. In: Phillips, M.R.; Al-Naemi, S., and Duarte, C.M. (eds.), Coastlines under Global Change: Proceedings from the International Coastal Symposium (ICS) 2024 (Doha, Qatar). Journal of Coastal Research, Special Issue No. 113, pp. 936-940. Charlotte (North Carolina), ISSN 0749-0208. Symbiosis establishment in juvenile scleractinian corals appears to be flexible and is possibly affected by various environment factors. How the onset of coral-algal symbiosis could be affected by changes in environmental conditions due to global warming was examined in this study using recruits of the coral Acropora tumida from Hong Kong, a marginal environment for coral growth. Different Symbiodinium subclades C1, C15 and D8-12 were provided to A. tumida recruits under different temperature [24, 27 (ambient), 30, 32°C] and salinity [32 (ambient), 27, 22 psu] treatments in a factorial experimental design. Successful uptake of the symbionts by A. tumida recruits was assessed visually under a microscope 14, 21 and 31 days after the first symbiont inoculation. Infection percentage and differences in mortality between recruits infected by different symbiont types under different conditions were assessed. The results indicated that recruits of A. tumida could be infected by all three subclades. However, elevated temperature impaired infection by C1 and C15 but not D8-12. Lowered salinities showed limited effect. No mortality difference was found among recruits infected by different symbiont types. Coral recruits did not seem to gain any advantage by forming symbiosis with D8-12 symbiont, higher infection rate may be more related to the aggressive behavior of subclade D symbionts. However, subclade D symbionts are reported to be less photosynthetically efficient, leading to lower growth rate in coral juveniles. Increasing seawater temperature may therefore drive the coral recruits to form symbiosis with less favorable symbionts. The implications of this on the future of coral community should be more seriously considered.