High tolerance to temperature and salinity change should enable scleractinian coral Platygyra acuta from marginal environments to persist under future climate change

Abstract

With projected changes in the marine environment under global climate change, the effects of single stressors on corals have been relatively well studied. However, more focus should be placed on the interactive effects of multiple stressors if their impacts upon corals are to be assessed more realistically. Elevation of sea surface temperature is projected under global climate change, and future increases in precipitation extremes related to the monsoon are also expected. Thus, the lowering of salinity could become a more common phenomenon and its impact on corals could be significant as extreme precipitation usually occurs during the coral spawning season. Here, we investigated the interactive effects of temperature [24, 27 (ambient), 30, 32°C] and salinity [33 psu (ambient), 30, 26, 22, 18, 14 psu] on larval settlement, post-settlement survival and early growth of the dominant coral Platygyra acuta from Hong Kong, a marginal environment for coral growth. The results indicate that elevated temperatures (+3°C and +5°C above ambient) did not have any significant effects on larval settlement success and post-settlement survival for up to 56 days of prolonged exposure. Such thermal tolerance was markedly higher than that reported in the literature for other coral species. Moreover, there was a positive effect of these elevated temperatures in reducing the negative effects of lowered salinity (26 psu) on settlement success. The enhanced settlement success brought about by elevated temperatures, together with the high post-settlement survival recorded up to 44 and 8 days of exposure under +3°C and +5°C ambient respectively, resulted in the overall positive effects of elevated temperatures on recruitment success. These results suggest that projected elevation in temperature over the next century should not pose any major problem for the recruitment success of P. acuta. The combined effects of higher temperatures and lowered salinity (26 psu) could even be beneficial. Therefore, corals that are currently present in marginal environments like Hong Kong, as exemplified by the dominant P. acuta, are likely to persist in a warmer and intermittently less saline, future ocean.

Effects of heat and hyposalinity on the gene expression in Acropora pruinosa larvae

“…Such information is extremely important to understand how coral larvae respond and cope with the highly dynamic natural field conditions. Interestingly, previous study on the larvae of another coral species in Hong Kong, Platygyra acuta, has shown high tolerance to elevated temperatures (+3 °C and +5 °C above ambient) that did not cause any negative effects on larval settlement success and post-settlement survival for up to 56 days of prolonged exposure (Chui and Ang, 2017). Further research is necessary to compare their molecular responses which might reveal the possible underlying mechanisms contributing to the difference in thermal tolerance among species.…”

“…While the effects of temperature stress on early stages of coral have been relatively well explored, there has been comparatively little focus on examining the salinity effect (Mayfield and Gates, 2007;Berkelmans et al, 2012). Reduction in salinity has been shown to reduce fertilization success (Richmond, 1993;Humphrey et al, 2008;Chui and Ang, 2015;Hedouin et al, 2015), increase developmental abnormality (Humphrey et al, 2008;Chui and Ang, 2015;Hedouin et al, 2015;Chui et al, 2016), and increase pre-and post-settlement mortality (Vermeij et al, 2006;Scott et al, 2013;Chui and Ang, 2017). Corals are known as osmoconformers (Hoegh-Guldberg and Smith, 1989).…”

“…Although studies have tested the effects of temperature or salinity on early life stages of coral, the potential combined impact of these multiple stressors on early developmental stages of corals has only starting to attract increasing attention in the recent decade (Chui and Ang, 2015;Chui et al, 2016;Chui and Ang, 2017;Dias et al, 2019;Ding et al, 2022). Responses to multiple stressors are more complex than those elicited under single stressor scenario, because the extent of effective response to single stressor may change or be modified at the presence of other stressors, which often resulted in an entirely new perspective on the capacity of organisms to respond (Hofmann and Todgham, 2010).…”