Differential responses of effective quantum yield to acute thermal stress in scleractinian corals including pre- and post-transplanted Acropora muricata

Abstract

Abstract. Jeetun S, Ricot M, Taleb-Hossenkhan N, Kaullysing D, Flot J-F, Bhagooli R. 2023. Differential responses of effective quantum yield to acute thermal stress in scleractinian corals including pre- and post-transplanted Acropora muricata. Indo Pac J Ocean Life 6: 54-63. Global climate change has had a serious impact on the health status of coral reefs and has led to the use of active reef restoration measures to remediate the decline in coral cover and assist in the recovery of depleted coral populations. This study aimed to assess the thermal photo-physiological responses of Acropora muricata pre- and post-transplantation from reef, lagoon, and nearshore stations to the experimental nearshore station and of four other non-transplanted coral species, namely, Acropora cytherea, Galaxea fascicularis, Pocillopora damicornis and Lithophyllon repanda from the reef. A visual assessment of dinoflagellate symbiont loss was conducted during summer bleaching events in 2011, 2016, and 2019 for A. muricata at the three stations, nearshore, lagoon, and reef, and for the other four corals at the reefs of Belle Mare (BM), Mauritius. The 2016 bleaching event appeared to be more severe for P. damicornis and L. repanda. A first experiment was carried out using pre-transplanted A. muricata from the reef, lagoon, and nearshore, respectively, in 2012, and a second one was conducted with post-transplanted A. muricata from the nearshore station in 2020, and A. cytherea, G. fascicularis, P. damicornis and L. repanda from the reef in both 2012 and 2020. The coral specimens were incubated at 28°C, 30°C, and 32°C for 3hrs. The results showed an enhanced photo-physiological thermo-tolerance through the measurement of the effective quantum yield of A. muricata following transplantation from the reef and lagoon to the nearshore station. Significantly different photo-physiological responses of the other four corals occurring on the reef were also reported between 2012 and 2020. These findings suggest that the nearshore transplanted A. muricata may have acclimatized, leading to enhanced thermo-tolerance when exposed to 30°C and A. cytherea among the test corals may have improved its thermo-tolerance at 30°C and 32°C possibly following several bleaching events. Further studies using longer experimental exposures and involving the symbiont species, antioxidant responses, symbiont cell density, and chlorophyll content along with coral genetics may shed light on possible mechanisms for such enhanced thermo-tolerance.