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Coral bleaching, bleaching-induced mortality, and the adaptive significance of the bleaching response

机译：珊瑚白化，白化导致的死亡率以及白化反应的适应性意义

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Coral bleaching events are often associated with higher levels of coral mortality but when this occurs in the chronology of individual bleaching events is poorly documented. Knowing when mortality occurs is important for understanding molecular mechanisms and the putative adaptive significance of the response (the Adaptive Bleaching Hypothesis). In a detailed study of a coral bleaching event on the Great Barrier Reef, involving weekly and twice weekly repetitive observations of >200 individually marked corals over an 18 month period (～ 16,000 observations), it is shown that bleaching in Acropora latistella, A. subulata and Turbinaria mesenterina was an acute, rapid response, occurring within days of a peak in seawater temperatures exceeding previously described thresholds. Subsurface light levels, measured over the duration of the event, were not anomalous. Full bleaching (i.e. whole colonies turning bone-white) and partial bleaching (white patches) was observed in the Acropora spp. whilst the T. mesenterina colonies typically paled to a light brown colour. Algal densities in bleached corals were 10-30% of those of normally pigmented corals (～2.5 × 10~6 algae per cm~2), and in this instance bleaching was clearly a sudden, isolated, stress event and not an extreme low-point in the seasonal fluctuation of the density of symbiotic algae. Bleached corals were associated with high levels of partial and whole-colony mortality, but mortality was exclusively limited to the two Acropora spp. Importantly, most of this mortality was recorded in surveys conducted 1 and 2 weeks after bleaching was first observed, and for A. latistella as little as 1 week after bleaching was first observed. This suggests that in this particular bleaching event, for the Acropora species, that bleaching and mortality were intimately linked: this in turn suggests it was a pathological phenomenon. The study highlights a problem in the adaptive bleaching hypothesis, whereby significant levels of mortality can occur in a bleaching event before any chance for subsequent recombination of the host-symbiont unit. It is argued that in order to further evaluate the significance of bleaching as a potentially adaptive mechanism, bleaching-induced and bleaching-related mortality have to be fully considered. It is necessary to incorporate the cost (in terms of mortality) of a bleaching event, the recurring cost of reverting to the original, mortal, stress-prone combination after the event, and the higher cost associated with forming a maladaptive combination.
机译：珊瑚褪色事件通常与更高的珊瑚死亡率有关，但是当这种情况发生时，单个漂白事件的时间记录很少。知道何时发生死亡率对于理解分子机制和应答的假定适应性意义非常重要（适应性漂白假说）。在对大堡礁珊瑚漂白事件的详细研究中，涉及在18个月内对200多个单独标记的珊瑚进行每周和每周两次的重复观测（〜16,000观测），结果表明，该现象在Acropora latistella，A.中存在。 subulata和Turbinaria mesenterina是一种急性快速反应，发生在海水温度超过上述阈值的峰值后的几天内。在事件持续时间内测得的地下光照水平并非异常。在Acropora spp中观察到完全漂白（即整个菌落变成白色）和部分漂白（白色斑块）。而肠系膜T.菌落通常呈浅棕色。漂白珊瑚中的藻类密度是正常色素珊瑚的藻类密度的10-30％（每平方厘米〜2.5×10〜6藻类），在这种情况下，漂白显然是突然的，孤立的压力事件，而不是极低的共生藻类密度的季节性波动点。漂白的珊瑚与高水平的部分和整个殖民地死亡率相关，但死亡率仅限于两个Acropora spp。重要的是，大部分死亡率是在首次观察到漂白后1和2周进行的调查中记录的，而对于A. latistella，仅在观察到漂白后1周进行了记录。这表明在这种特定的漂白事件中，对于棘足类物种而言，漂白和死亡率密切相关：这反过来表明这是一种病理现象。该研究突出了适应性漂白假说中的一个问题，即在漂白事件中，如果在随后的宿主共生体单元重组之前没有任何机会，则会导致相当高的死亡率。有人认为，为了进一步评估漂白作为一种潜在适应机制的重要性，必须充分考虑漂白引起的死亡率和与漂白有关的死亡率。有必要将漂白事件的成本（就死亡率而言），事件后恢复为原始的，致命的，易受压力影响的组合的重复成本，以及与适应不良的组合相关的较高成本进行合并。

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  • 来源
    《Marine biology》 |2008年第1期|p.65-80|共16页
  • 作者

    Ross J. Jones;

  • 作者单位

    Bermuda Institute of Ocean Sciences (BIOS), 17 Biological Lane, Ferry Reach, St George's GE01, Bermuda;

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  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 环境生物学;
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