圖片提供: R. REEF ET AL., PLOS ONE 4 (11) (NOVEMBER 2009)
寄生在珊瑚礁上多少有點(diǎn)兒像在日光浴床上生活一樣。隨著太陽(yáng)光穿透海水并反射到珊瑚礁上,，這些光線會(huì)穿透珊瑚,、與珊瑚共生的促進(jìn)光合作用的海藻，以及其他生活在珊瑚礁上的生物,。那么究竟是什么原因讓這些生物避免了被烤焦的厄運(yùn)呢,？一項(xiàng)新的研究表明，正是珊瑚在這里起到了遮光劑的作用——它能夠吸收紫外線,，并減少其對(duì)生活在珊瑚礁上的居民的傷害,。
之前的研究表明，構(gòu)成礁體的珊瑚的碳酸鈣外骨骼能夠在紫外光下發(fā)出熒光,，這意味著珊瑚礁能夠吸收紫外線,。為了搞清這種物質(zhì)是否能夠保護(hù)生活在珊瑚礁上的有機(jī)體，澳大利亞昆士蘭大學(xué)的海洋生物學(xué)家Ruth Reef和同事對(duì)海葵（Aiptasia pulchella）進(jìn)行了研究,。這些珊瑚的親戚具有同前者類似的組織,，并且同樣是共生光合海藻的家。
在實(shí)驗(yàn)室中,，研究小組將?？旁谏汉鞴羌芑虬咨U管的上面。與鉛管不同,，珊瑚骨架幾乎能夠吸收所有有害的紫外線,，并釋放出黃色的熒光。此外,，與放在鉛管上的?？啾龋旁谏汉魃系暮,？邮艿淖贤廨椛渲皇乔罢叩?/4,，并且它們?cè)馐艿拿撗鹾颂呛怂幔―NA）損傷也僅是前者的1/7。即便將這些珊瑚骨架研磨成細(xì)小的粉末,，研究小組依然發(fā)現(xiàn)了類似的現(xiàn)象,，這意味著這種保護(hù)作用是因?yàn)樯汉鞴羌艿幕瘜W(xué)構(gòu)成所致，而不是其粗糙而復(fù)雜的表面對(duì)紫外線產(chǎn)生的散射作用,。研究小組在11月25日的《科學(xué)公共圖書館—綜合》網(wǎng)絡(luò)版上報(bào)告了這一研究成果,。
Reef指出,，生活在海洋中的許多光合生物也會(huì)形成碳酸鈣,，而它們也可能通過(guò)這種方式保護(hù)自己免受紫外線輻射。她說(shuō)：“石灰化過(guò)程大約出現(xiàn)在6億年前,，當(dāng)時(shí)的紫外線水平要遠(yuǎn)遠(yuǎn)高于今天,。”此外，Reef強(qiáng)調(diào),，在大約發(fā)生于5.3億年前的寒武紀(jì)大爆發(fā)期間,，珊瑚骨骼異常豐富且多樣，這可能反映了“該時(shí)期自然界對(duì)珊瑚積聚的一種迫切需求,，那時(shí)許多生物體都向著較淺且富含氧氣的水域遷徙,，而那里的紫外線水平都很高”。摩納哥科學(xué)中心——一所海洋學(xué)研究機(jī)構(gòu)——的科學(xué)主管Denis Allemand則表示：“這種新發(fā)現(xiàn)的特性是宿主針對(duì)共生生物的一種額外的,、意想不到的適應(yīng),。”
Reef和同事注意到，蝎子,、蜘蛛,，以及其他一些生物在暴露于紫外線下時(shí)也會(huì)發(fā)出熒光，這意味著遮光劑效應(yīng)不止進(jìn)化了一次。（生物谷Bioon.com）
生物谷推薦原始出處：
PLoS ONE 4(11): e7995. doi:10.1371/journal.pone.0007995
Coral Skeletons Defend against Ultraviolet Radiation
Ruth Reef*, Paulina Kaniewska, Ove Hoegh-Guldberg
Centre for Marine Studies and the Austrailan Research Council (ARC) Centre of Excellence for Coral Reef Studies, The University of Queensland, St Lucia, Queensland, Australia
Background
Many coral reef organisms are photosynthetic or have evolved in tight symbiosis with photosynthetic symbionts. As such, the tissues of reef organisms are often exposed to intense solar radiation in clear tropical waters and have adapted to trap and harness photosynthetically active radiation (PAR). High levels of ultraviolet radiation (UVR) associated with sunlight, however, represent a potential problem in terms of tissue damage.
Methodology/Principal Findings
By measuring UVR and PAR reflectance from intact and ground bare coral skeletons we show that the property of calcium carbonate skeletons to absorb downwelling UVR to a significant extent, while reflecting PAR back to the overlying tissue, has biological advantages. We placed cnidarians on top of bare skeletons and a UVR reflective substrate and showed that under ambient UVR levels, UVR transmitted through the tissues of cnidarians placed on top of bare skeletons were four times lower compared to their counterparts placed on a UVR reflective white substrate. In accordance with the lower levels of UVR measured in cnidarians on top of coral skeletons, a similar drop in UVR damage to their DNA was detected. The skeletons emitted absorbed UVR as yellow fluorescence, which allows for safe dissipation of the otherwise harmful radiation.
Conclusions/Significance
Our study presents a novel defensive role for coral skeletons and reveals that the strong UVR absorbance by the skeleton can contribute to the ability of corals, and potentially other calcifiers, to thrive under UVR levels that are detrimental to most marine life.
