Seawater carbonate chemistry, survival, metamorphosis and respiration rate of coral Acropora digitifera during experiments, 2011@en

Ocean acidification may negatively impact the early life stages of some marine invertebrates including corals. Although reduced growth of juvenile corals in acidified seawater has been reported, coral larvae have been reported to demonstrate some level of tolerance to reduced pH. We hypothesize that the observed tolerance of coral larvae to low pH may be partly explained by reduced metabolic rates in acidified seawater because both calcifying and non-calcifying marine invertebrates could show metabolic depression under reduced pH in order to enhance their survival. In this study, after 3-d and 7-d exposure to three different pH levels (8.0, 7.6, and 7.3), we found that the oxygen consumption of Acropora digitifera larvae tended to be suppressed with reduced pH, although a statistically significant difference was not observed between pH conditions. Larval metamorphosis was also observed, confirming that successful recruitment is impaired when metamorphosis is disrupted, despite larval survival. Results also showed that the metamorphosis rate significantly decreased under acidified seawater conditions after both short (2 h) and long (7 d) term exposure. These results imply that acidified seawater impacts larval physiology, suggesting that suppressed metabolism and metamorphosis may alter the dispersal potential of larvae and subsequently reduce the resilience of coral communities in the near future as the ocean pH decreases.海洋酸化可能对包括珊瑚在内的部分海洋无脊椎动物的早期生命阶段产生负面影响。尽管已有研究报道酸化海水中幼珊瑚的生长受到抑制，但现有研究表明珊瑚幼虫对pH降低具有一定程度的耐受性。本研究提出如下假说：珊瑚幼虫对低pH的已观测到的耐受性，可部分通过酸化海水中代谢速率降低得到解释——因为无论是钙化还是非钙化海洋无脊椎动物，在pH降低的环境下均可表现出代谢抑制以提升自身存活率。本研究中，将指状轴孔珊瑚（Acropora digitifera）幼虫分别暴露于三种pH水平（8.0、7.6、7.3）的水体中，暴露时长分别为3天与7天，结果发现尽管各pH条件间未观测到统计学显著性差异，但幼虫的耗氧量随pH降低呈现出受抑制的趋势。研究同时对幼虫变态发育进行了观测，证实即便幼虫能够存活，若变态发育过程遭到破坏，珊瑚幼体的成功补充仍会受损。结果还显示，无论是短期（2小时）还是长期（7天）暴露于酸化海水环境中，幼虫的变态发育率均出现显著下降。上述结果表明，酸化海水会对幼虫的生理机能产生影响，这意味着代谢抑制与变态发育受阻可能会改变幼虫的扩散潜力，并随着未来海洋pH持续降低，最终削弱珊瑚群落的恢复能力。