Middlebrook Rachael, Hoegh-Guldberg Ove, Leggat William
Centre for Marine Studies and ARC Centre of Excellence for Coral Reef Studies, University of Queensland, St Lucia, QLD 4072, Australia.
J Exp Biol. 2008 Apr;211(Pt 7):1050-6. doi: 10.1242/jeb.013284.
The mutualistic relationship between corals and their unicellular dinoflagellate symbionts (Symbiodinium sp.) is a fundamental component within the ecology of coral reefs. Thermal stress causes the breakdown of the relationship between corals and their symbionts (bleaching). As with other organisms, this symbiosis may acclimate to changes in the environment, thereby potentially modifying the environmental threshold at which they bleach. While a few studies have examined the acclimation capacity of reef-building corals, our understanding of the underlying mechanism is still in its infancy. The present study focused on the role of recent thermal history in influencing the response of both corals and symbionts to thermal stress, using the reef-building coral Acropora aspera. The symbionts of corals that were exposed to 31 degrees C for 48 h (pre-stress treatment) 1 or 2 weeks prior to a 6-day simulated bleaching event (when corals were exposed to 34 degrees C) were found to have more effective photoprotective mechanisms. These mechanisms included changes in non-photochemical quenching and xanthophyll cycling. These differences in photoprotection were correlated with decreased loss of symbionts, with those corals that were not prestressed performing significantly worse, losing over 40% of their symbionts and having a greater reduction in photosynthetic efficiency. These results are important in that they show that thermal history, in addition to light history, can influence the response of reef-building corals to thermal stress and therefore have implications for the modeling of bleaching events. However, whether acclimation is capable of modifying the thermal threshold of corals sufficiently to cope as sea temperatures increase in response to global warming has not been fully explored. Clearly increases in sea temperatures that extend beyond 1-2 degrees C will exhaust the extent to which acclimation can modify the thermal threshold of corals.
珊瑚与其单细胞双鞭毛藻共生体（共生藻属）之间的互利共生关系是珊瑚礁生态系统的一个基本组成部分。热应激会导致珊瑚与其共生体之间的关系破裂（白化）。与其他生物一样，这种共生关系可能会适应环境变化，从而有可能改变它们白化的环境阈值。虽然有一些研究探讨了造礁珊瑚的适应能力，但我们对其潜在机制的理解仍处于起步阶段。本研究以造礁珊瑚粗糙鹿角珊瑚为对象，重点研究近期热历史在影响珊瑚及其共生体对热应激反应方面的作用。在为期6天的模拟白化事件（珊瑚暴露于34摄氏度）之前1周或2周，将珊瑚的共生体暴露于31摄氏度下48小时（应激前处理），结果发现这些共生体具有更有效的光保护机制。这些机制包括非光化学猝灭和叶黄素循环的变化。这些光保护方面的差异与共生体损失的减少相关，未经过应激前处理的珊瑚表现明显更差，损失了超过40%的共生体，光合效率也有更大幅度的降低。这些结果很重要，因为它们表明热历史除了光照历史外，也会影响造礁珊瑚对热应激的反应，因此对白化事件的建模有影响。然而，适应是否能够充分改变珊瑚的热阈值以应对全球变暖导致的海水温度上升，尚未得到充分研究。显然，超过1 - 2摄氏度的海水温度升高将超出适应能够改变珊瑚热阈值的程度。
