我实验室高坤山教授课题组与台湾海洋生物博物馆（National Museum of Marine Biology and Aquarium, NMMBA）在Photochemistry and Photobiology发表合作研究论文（Incident ultraviolet irradiances influence physiology, development and settlement of larva in the coral Pocillopora damicornis，2016），表明紫外辐射对珊瑚幼体的生长发育有抑制作用。

珊瑚礁是世界上生产力最高、生物多样性最丰富，也是最易受到全球气候变化威胁的海洋生态系统之一。珊瑚繁殖与幼体补充过程对于全球珊瑚礁生物多样性的保护与保育具有重要的意义。珊瑚的有性生殖基本分为两种：一种是珊瑚成体将配子释放到水体中，进行体外受精，受精卵在水体中发育为浮浪幼体（planula），此种生殖方式称为“排放型”（broadcast spawning）；另一种是珊瑚成体向水体中释放精子，而精子进入孕育有卵子的珊瑚虫中进行体内受精，直到受精卵发育为浮浪幼体，才将其释放到水体中，此种生殖方式称为“卵生型”（brooding）。珊瑚与共生甲藻（Symbiodinium）之间的互利共生，使得其可以在寡营养的热带海域广泛生存。一般情况下，对于“排放型”幼体来说，这种共生关系是在浮浪幼体完成变态并附着到底质后，才从周围水体中吸引共生藻，建立起来的；而对于“卵生型”释放的浮浪幼体来说，其会直接从母体珊瑚中“继承”共生藻。过去的研究已经表明幼体中共生关系的存在，有利于提高幼体的成活率及竞争力，而在这其中共生藻可能起了重要的作用。

高坤山教授课题组通过将从“卵生型”的鹿角枝形珊瑚（Pocillopora damicornis）收集到的浮浪幼体暴露于紫外辐射（UVR，280-400 nm）下，研究了幼体生长发育及其内共生藻光合作用等生理过程的响应。结果发现幼体的成活率、变态率及附着率在紫外暴露后均下降了22-25%，而这一抑制作用在UV-A（315-400 nm）波段即有明显的体现。同时，幼体中共生藻的光合速率在UV-B（280-315 nm）和UV-A的共同作用下也明显降低，使得珊瑚-藻共生体由自养型变成异养型。这其中主要是UV-B的抑制作用，而UV-A的效应不明显或者略有促进作用。这些结果表明珊瑚幼体可能利用体内的紫外吸收物质，如三苯甲咪唑类氨基酸（MAAs）、荧光蛋白等，屏蔽了一部分的UV-A，从而缓解了UV-A对共生藻的威胁，使得共生藻的光合作用主要受到UV-B的抑制。幼体在紫外吸收物质合成过程中消耗了大量的能量，从而没有足够的能量来进行变态以及附着，最终可能影响珊瑚礁的幼体补充及修复再生的过程。本研究是我国目前首次涉及珊瑚浮浪幼体内共生藻光合生理过程的环境响应研究，该成果有助于加深珊瑚与共生藻间共生机制的理解。

Abstract:

Ultraviolet radiation (UVR, 280–400 nm) is one of the potential factors involved in the induction of coral bleaching, loss of the endosymbiotic dinoflagellate Symbiodinium or their photosynthetic pigments. However, little has been documented on its effects on the behavior and recruitment of

coral larvae, which sustains coral reef ecosystems. Here, we analyzed physiological changes in larvae of the scleractinian coral Pocillopora damicornis and examined the photophysiological performance of the symbiont algae, following exposure to incident levels of UVR and subsequently observed the development of coral larvae. The endosymbiotic algae exhibited a high sensitivity to UV-B (295 –320 nm) during a 6 h exposure, showing lowered photosynthetic performance per

larva and per algal cell, whereas the presence of UV-A (320–395 nm) significantly stimulated photosynthesis. UVR decreased chlorophyll a concentration only at higher surface temperature or at the higher doses or intensities of UVR. Correlations between UV-absorbing compound (UVAC) con-tents or UVR sensitivity and temperature were identified, implying that UVACs might act as a screen or antioxidants in Pocillopora damicornis larvae. Larvae reared under UVR exposures showed lower levels of survivorship, metamorphosis and settlement, with inhibition by UV-A being much greater than that caused by UV-B.

Reference: Zhou J, Fan T-Y, Beardall J, Gao K (2016) Incident ultraviolet irradiances influence physiology, development and settlement of larva in the coral Pocillopora damicornis. Photochemistry and Photobiology 92:293-300

Link to full text: http://onlinelibrary.wiley.com/doi/10.1111/php.12567/pdf