Metabolic rates and tissue composition of the coral Pocillopora verrucosa over 12 latitudes in the Red Sea characterized by strong temperature and nutrient gradient

Global warming was reported to cause growth reductions in tropical shallow water corals in both, cooler and warmer, regions of the coral species range. This suggests regional adaptation with less heat-tolerant populations in cooler and more thermo-tolerant populations in warmer regions. Here, we investigated seasonal changes in the in situ metabolic performance of the widely distributed hermatypic coral Pocillopora verrucosa along 12 degrees latitudes featuring a steep temperature gradient between the northern (28.5 degrees N, 21-27 degrees C) and southern (16.5 degrees N, 28-33 degrees C) reaches of the Red Sea. Surprisingly, we found little indication for regional adaptation, but strong indications for high phenotypic plasticity: Calcification rates in two seasons (winter, summer) were found to be highest at 28-29 degrees C throughout all populations independent of their geographic location. Mucus release increased with temperature and nutrient supply, both being highest in the south. Genetic characterization of the coral host revealed low inter-regional variation and differences in the Symbiodinium clade composition only at the most northern and most southern region. This suggests variable acclimatization potential to ocean warming of coral populations across the Red Sea: high acclimatization potential in northern populations, but limited ability to cope with ocean warming in southern populations already existing at the upper thermal margin for corals

据报道，全球变暖会导致热带浅水珊瑚在其分布范围的较冷与较暖区域均出现生长速率下降的情况。这提示存在区域适应性：分布于较冷区域的珊瑚种群耐热性较弱，而分布于较暖区域的种群耐热性更强。本研究针对分布广泛的造礁珊瑚（hermatypic coral）疣状杯形珊瑚（Pocillopora verrucosa），沿红海跨越12个纬度的样带开展原位（in situ）代谢表现的季节动态调查，该样带南北两端存在显著的温度梯度：北部采样点位于28.5°N，水温范围为21~27℃；南部采样点位于16.5°N，水温范围为28~33℃。令人意外的是，本研究未发现显著的区域适应性信号，却观测到极强的表型可塑性（phenotypic plasticity）证据：在冬季与夏季两个季节，所有珊瑚种群的钙化速率均在28~29℃时达到峰值，且这一结果与种群的地理分布无关。黏液释放量随温度与营养盐供给水平升高而增加，且在南部种群中达到最高值。对珊瑚宿主的遗传特征分析显示，区域间的遗传变异水平较低，仅在最北端与最南端的种群中，虫黄藻（Symbiodinium）分支组成存在差异。这表明红海不同区域的珊瑚种群对海洋变暖的驯化潜力存在显著差异：北部种群具备较高的驯化适应潜力，而南部种群已处于珊瑚生存的热极限边缘，应对海洋变暖的能力极为有限。