Seawater carbonate chemistry and biological processes of Porites panamensis during experiments, 2011

Survival of coral planulae, and the successful settlement and healthy growth of primary polyps are critical for the dispersal of scleractinian corals and hence the recovery of degraded coral reefs. It is therefore important to explore how the warmer and more acidic oceanic conditions predicted for the future could affect these processes. This study used controlled culture to investigate the effects of a 1 °C increase in temperature and a 0.2-0.25 unit decrease in pH on the settlement and survival of planulae and the growth of primary polyps in the Tropical Eastern Pacific coral Porites panamensis. We found that primary polyp growth was reduced only marginally by more acidic seawater but the combined effect of high temperature and lowered pH caused a significant reduction in growth of primary polyps by almost a third. Elevated temperature was found to significantly reduce the amount of zooxanthellae in primary polyps, and when combined with lowered pH resulted in a significant reduction in biomass of primary polyps. However, survival and settlement of planula larvae were unaffected by increased temperature, lowered acidity or the combination of both. These results indicate that in future scenarios of increased temperature and oceanic acidity coral planulae will be able to disperse and settle successfully but primary polyp growth may be hampered. The recovery of reefs may therefore be impeded by global change even if local stressors are curbed and sufficient sources of planulae are available.珊瑚浮浪幼虫（coral planulae）的存活、初生珊瑚体（primary polyps）的成功附着与健康生长，对于石珊瑚（scleractinian corals）的扩散以及退化珊瑚礁的修复均至关重要。因此，探究未来预测中海洋温度升高、酸度增强的环境将如何影响这些过程，具有重要的科学意义。本研究采用受控培养实验，探究了温度升高1℃、pH值降低0.2-0.25个单位的复合环境条件，对东热带太平洋巴拿马滨珊瑚（Porites panamensis）的浮浪幼虫附着与存活，以及初生珊瑚体生长的影响。研究结果显示：酸性增强的海水仅会对初生珊瑚体的生长产生小幅抑制作用，但高温与低pH的联合胁迫会使初生珊瑚体的生长量显著降低近三分之一；高温会显著减少初生珊瑚体内的虫黄藻（zooxanthellae）数量，若同时伴随pH降低，则会进一步导致初生珊瑚体的生物量显著下降。不过，浮浪幼虫的存活与附着过程，并未受到温度升高、酸度降低或二者联合作用的显著影响。上述结果表明，在未来温度升高与海洋酸化的情景下，珊瑚浮浪幼虫仍可顺利完成扩散与附着，但初生珊瑚体的生长可能会受到显著阻碍。即便当地的环境胁迫因素得到遏制、且浮浪幼虫的种源充足，全球变化仍可能阻碍珊瑚礁的自然修复进程。