Bermuda Institute of Ocean Sciences (BIOS), 17 Ferry Reach, St George's GE01, Bermuda.
Department of Biological Sciences, Lehigh University, Bethlehem, PA 18015, USA.
J Exp Biol. 2022 Jul 1;225(13). doi: 10.1242/jeb.244196. Epub 2022 Jul 8.
Temperature is a key driver of metabolic rates. So far, we know little about potential physiological adjustments of subtropical corals to seasonal temperature changes (>8°C) that substantially exceed temperature fluctuation experienced by their counterparts in the tropics. This study investigated the effect of temperature reductions on Montastraea cavernosa and Porites astreoides in Bermuda (32°N; sea surface temperature ∼19-29°C) over 5 weeks, applying the following treatments: (i) constant control temperature at 28°C, and (ii) temperature reduction (0.5°C day-1) followed by constant temperature (20 days; acclimatization period) at 24°C and (iii) at 20°C. Both species decreased photosynthesis and respiration during temperature reduction as expected, which continued to decrease during the acclimatization period, indicating adjustment to a low energy turnover rather than thermal compensation. Trajectories of physiological adjustments and level of thermal compensation, however, differed between species. Montastraea cavernosa zooxanthellae metrics showed a strong initial response to temperature reduction, followed by a return to close to control values during the acclimatization period, reflecting a high physiological flexibility and low thermal compensation. Porites astreoides zooxanthellae, in contrast, showed no initial response, but an increase in pigment concentration per zooxanthellae and similar photosynthesis rates at 24°C and 20°C at the end of the experiment, indicating low acute thermal sensitivity and the ability for thermal compensation at the lowest temperature. Respiration decreased more strongly than photosynthesis, leading to significant build-up of biomass in both species (energy reserves). Results are important in the light of potential poleward migration of corals and of potential latitudinal and species-specific differences in coral thermal tolerance.
温度是代谢率的关键驱动因素。到目前为止，我们对亚热带珊瑚潜在的生理适应机制知之甚少，这些适应机制可能会导致季节性温度变化（超过 8°C），而这种温度变化大大超过了热带珊瑚所经历的温度波动。本研究调查了温度降低对百慕大（32°N；海面温度约为 19-29°C）的 Montastraea cavernosa 和 Porites astreoides 的影响，实验持续了 5 周，应用了以下处理：（i）恒定控制温度为 28°C，（ii）温度降低（0.5°C/day），随后在 24°C 下进行恒定温度（20 天；适应期），（iii）在 20°C。两种珊瑚在温度降低期间，如预期的那样，光合作用和呼吸作用均降低，在适应期内持续降低，表明它们适应了低能量转换，而不是热补偿。然而，生理适应的轨迹和热补偿的水平在物种之间存在差异。Montastraea cavernosa 虫黄藻指标显示出对温度降低的强烈初始响应，随后在适应期内恢复到接近对照值，这反映出其具有高生理灵活性和低热补偿。相比之下，Porites astreoides 虫黄藻没有初始响应，但在实验结束时，其藻内色素浓度增加，光合作用率在 24°C 和 20°C 时相似，这表明其对热的急性敏感性较低，并且在最低温度下具有热补偿能力。呼吸作用比光合作用下降得更强烈，导致两种珊瑚的生物量（能量储备）都显著增加。这些结果在珊瑚可能向极地迁移的背景下非常重要，同时也说明了珊瑚对温度的耐受性存在潜在的纬度和物种特异性差异。
