Adaptation strategies of the corallimorpharian Rhodactis rhodostoma to irradiance and temperature
Adaptation strategies of the corallimorpharian Rhodactis rhodostoma to irradiance and temperature
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DOI：
10.1007/s00227-006-0589-5
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发表时间：
2007-05-01
期刊：
影响因子：
2.4
通讯作者：
Chadwick, Nanette E.
中科院分区：
文献类型：
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作者：
Kuguru, Baraka;Winters, Gidon;Chadwick, Nanette E.
珊瑚虫可能在珊瑚礁的某些栖息地占据主导地位，并与石珊瑚竞争获得光线，但对它们的光合特性知之甚少。在埃拉特在北方红海，我们观察到，丰富的个体的珊瑚Rhodactis rhodostoma的珊瑚礁斜坡上的深度显着下降。现场和实验室实验表明，他们采用几种机制的光适应高辐照浅礁坪。它们的内共生微藻（虫黄藻）的丰度和叶绿素含量随光照水平的变化显着。用脉冲幅度调制荧光计测定了红毛藻的虫黄藻。当实验暴露于强光（HL）与弱光（LL）时，红口藻通过在光系统II上表达显著更高的非光化学猝灭和最大激发压力值来有效地分散过量的光能。宿主珊瑚虫组织通过屏蔽藻类共生体免受高辐照来介导这种反应。HL的寄主触手内胚层明显增厚，微藻细胞距离中胶层较LL远。珊瑚虫宿主的虫黄藻分支也随深度而变化。在浅水中，所有采样的个体都寄生着分支C虫黄藻，而在深水中，大多数个体都寄生着分支D。结果表明，在不同的生长阶段，红毛菊的光合产量均高于其它两个品种。rhodostoma的影响较小HL比石珊瑚检查。当同时暴露于高温（HT）和HL条件下时，R. rhodostoma降低了它们的最大量子产率，但在低温（LT）下暴露于HL时没有降低。与此相反，殖民地的石珊瑚Favia favus减少了他们的光合输出时，暴露于HL在两个温度制度。高温胁迫2周后，R.珊瑚红口藻似乎完全变白，但在恢复到环境温度时重新建立了它们的虫黄藻种群。我们的结论是，内共生虫黄藻和宿主珊瑚虫对高辐射的光适应机制可以部分解释R。一些浅礁滩上的红口藻珊瑚虫在高温下存活数周的能力，也可能使珊瑚虫在被热应力杀死的珊瑚礁浅水区重新繁殖。
Corallimorpharians may dominate some habitats on coral reefs and compete with stony corals for access to light, yet little is known concerning their photosynthetic traits. At Eilat in the northern Red Sea, we observed that the abundance of individuals of the corallimorpharian Rhodactis rhodostoma decreased significantly with depth on the reef slope. Field and laboratory experiments revealed that they employ several mechanisms of photoadaptation to high irradiance on the shallow reef flat. Their endosymbiotic microalgae (zooxanthellae) varied significantly in both abundance and chlorophyll content with level of irradiance. Use of a diving pulse amplitude modulated fluorometer revealed that the zooxanthellae of R. rhodostoma effectively disperse excess light energy by expressing significantly higher values of non-photochemical quenching and maximum excitation pressure on photosystem II when experimentally exposed to high light (HL) versus low light (LL). Host corallimorpharian tissues mediated this response by shielding the algal symbionts from high irradiance. The endoderm of host tentacles thickened significantly and microalgal cells were located further from the mesoglea in HL than in LL. The clades of zooxanthellae hosted by the corallimorpharians also varied with depth. In shallow water, all sampled individuals hosted clade C zooxanthellae, while in deep water the majority hosted clade D. The photosynthetic output of individuals of R. rhodostoma was less affected by HL than was that of a stony coral examined. When exposed to both high temperature (HT) and HL, individuals of R. rhodostoma reduced their maximum quantum yield, but not when exposed to HL at low temperature (LT). In contrast, colonies of the scleractinian coral Favia favus reduced their photosynthetic output when exposed to HL in both temperature regimes. After 2 weeks of HT stress, R. rhodostoma polyps appeared to bleach completely but re-established their zooxanthella populations upon return to ambient temperature. We conclude that mechanisms of photoadaptation to high irradiance employed by both the endosymbiotic zooxanthellae and host corallimorpharians may explain in part the abundance of R. rhodostoma on some shallow reef flats. The ability to survive for weeks at HT while bleached also may allow corallimorpharians to repopulate shallow reef areas where scleractinians have been killed by thermal stress.