School of Zoology, The George S. Wise Faculty of Life Sciences, Tel-Aviv University, Tel-Aviv, 69978, Israel; The Interuniversity Institute for Marine Sciences, Eilat, 8810302, Israel.
The Interuniversity Institute for Marine Sciences, Eilat, 8810302, Israel; The Mina and Everard Goodman Faculty of Life Sciences, Bar Ilan University, Ramat Gan, 5290002, Israel.
Mar Environ Res. 2021 Jan;163:105215. doi: 10.1016/j.marenvres.2020.105215. Epub 2020 Nov 24.
Coral reefs are threatened worldwide by global climate change, manifested in anthropogenic ocean warming and acidification. Despite the importance of coral sexual reproduction for the continuity of coral reefs, our understanding of the extent of the impact of climate change on coral sexual reproduction, particularly on coral reproductive phenology and early life stages, is limited. Here, we experimentally examined the effects of predicted end-of-the-century seawater conditions on the sexual reproduction and photosynthetic capacity of a Red-Sea zooxanthellate octocoral, Rhytisma fulvum. Sexually mature colonies were exposed to ambient temperature and pH conditions and to Representative Concentration Pathway (RCP) conditions (4.5 and 8.5), five weeks prior to their expected surface-brooding event. The reproductive phenology of the colonies under the simulated seawater conditions was compared to that on the natural reef. In addition, subsequent planulae development and their metamorphosis into primary polyps under the same RCP conditions as their parent colonies were monitored in a running seawater system. The results reveal that both RCP conditions led to a change in the timing of onset of the surface-brooding event and its synchronicity. In contrast, the surface-brooding event under ambient conditions co-occurred with that of the in-situ reef colonies and maintained its synchrony. Similarly, planula survival and polyp metamorphosis rate were significantly reduced under both RCP conditions compared to propagules reared under ambient conditions. In addition, the photosynthetic capacity of the parent colonies under both RCPs showed a reduction relative to that under the ambient conditions in the experiment, suggesting a reduction in carbon fixation during the late stages of gametogenesis. While our findings indicate that octocoral reproductive phenology is affected by environmental changes, further work is required in order to elucidate the long-term implications for the R. fulvum population in the northern Red Sea.
珊瑚礁受到全球气候变化的威胁，表现为人为的海洋变暖与酸化。尽管珊瑚的有性繁殖对珊瑚礁的延续很重要，但我们对气候变化对珊瑚有性繁殖的影响程度，特别是对珊瑚繁殖物候和早期生活阶段的影响程度的理解是有限的。在这里，我们通过实验研究了预测的本世纪末海水条件对红海有虫黄藻共生八放珊瑚 Rhytisma fulvum 的有性繁殖和光合作用能力的影响。在预期的表面产卵事件发生前五周，将性成熟的群体暴露于环境温度和 pH 值条件以及代表性浓度途径（RCP）条件（4.5 和 8.5）下。将模拟海水中的群体的繁殖物候与自然珊瑚礁上的繁殖物候进行了比较。此外，在与母群体相同的 RCP 条件下，在一个流水海水系统中监测了随后的浮游幼虫发育及其变态为初级息肉的情况。结果表明，两种 RCP 条件都导致了表面产卵事件开始时间及其同步性的改变。相比之下，在环境条件下的表面产卵事件与现场珊瑚礁上的产卵事件同时发生并保持同步。同样，与在环境条件下饲养的幼虫相比，在两种 RCP 条件下，浮游幼虫的存活率和息肉变态率均显著降低。此外，与实验中的环境条件相比，两种 RCP 条件下母群体的光合作用能力都有所降低，这表明在配子发生的后期阶段，碳固定减少。虽然我们的研究结果表明，八放珊瑚的繁殖物候受到环境变化的影响，但需要进一步的研究才能阐明这对北红海 R. fulvum 种群的长期影响。
