我實驗室高坤山教授課題組與臺灣海洋生物博物館（National Museum of Marine Biology and Aquarium, NMMBA）在Photochemistry and Photobiology發表合作研究論文（Incident ultraviolet irradiances influence physiology, development and settlement of larva in the coral Pocillopora damicornis，2016），表明紫外輻射對珊瑚幼體的生長發育有抑制作用。

珊瑚礁是世界上生產力最高、生物多樣性最豐富，也是最易受到全球氣候變化威脅的海洋生態系統之一。珊瑚繁殖與幼體補充過程對于全球珊瑚礁生物多樣性的保護與保育具有重要的意義。珊瑚的有性生殖基本分為兩種：一種是珊瑚成體將配子釋放到水體中，進行體外受精，受精卵在水體中發育為浮浪幼體（planula），此種生殖方式稱為“排放型”（broadcast spawning）；另一種是珊瑚成體向水體中釋放精子，而精子進入孕育有卵子的珊瑚蟲中進行體內受精，直到受精卵發育為浮浪幼體，才將其釋放到水體中，此種生殖方式稱為“卵生型”（brooding）。珊瑚與共生甲藻（Symbiodinium）之間的互利共生，使得其可以在寡營養的熱帶海域廣泛生存。一般情況下，對于“排放型”幼體來說，這種共生關系是在浮浪幼體完成變態并附著到底質后，才從周圍水體中吸引共生藻，建立起來的；而對于“卵生型”釋放的浮浪幼體來說，其會直接從母體珊瑚中“繼承”共生藻。過去的研究已經表明幼體中共生關系的存在，有利于提高幼體的成活率及競爭力，而在這其中共生藻可能起了重要的作用。

高坤山教授課題組通過將從“卵生型”的鹿角枝形珊瑚（Pocillopora damicornis）收集到的浮浪幼體暴露于紫外輻射（UVR，280-400 nm）下，研究了幼體生長發育及其內共生藻光合作用等生理過程的響應。結果發現幼體的成活率、變態率及附著率在紫外暴露后均下降了22-25%，而這一抑制作用在UV-A（315-400 nm）波段即有明顯的體現。同時，幼體中共生藻的光合速率在UV-B（280-315 nm）和UV-A的共同作用下也明顯降低，使得珊瑚-藻共生體由自養型變成異養型。這其中主要是UV-B的抑制作用，而UV-A的效應不明顯或者略有促進作用。這些結果表明珊瑚幼體可能利用體內的紫外吸收物質，如三苯甲咪唑類氨基酸（MAAs）、熒光蛋白等，屏蔽了一部分的UV-A，從而緩解了UV-A對共生藻的威脅，使得共生藻的光合作用主要受到UV-B的抑制。幼體在紫外吸收物質合成過程中消耗了大量的能量，從而沒有足夠的能量來進行變態以及附著，最終可能影響珊瑚礁的幼體補充及修復再生的過程。本研究是我國目前首次涉及珊瑚浮浪幼體內共生藻光合生理過程的環境響應研究，該成果有助于加深珊瑚與共生藻間共生機制的理解。

Abstract:

Ultraviolet radiation (UVR, 280–400 nm) is one of the potential factors involved in the induction of coral bleaching, loss of the endosymbiotic dino?agellate 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 coralPocillopora 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) signi?cantly 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 identi?ed, 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