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海水酸化威胁珊瑚生存

海水酸化威胁珊瑚生存

海洋酸化(ocean acidification)主要是工业生产排放的二氧化碳溶解到海水中造成的。海水应为弱碱性,但过量的二氧化碳排放已使海水表层pH值降低。海水酸性的增加,会改变海水的种种化学平衡,使多种海洋生物乃至生态系统面临巨大威胁。

日前,日本东京大学研究生院的一项最新研究发现,海水酸化越严重,拥有坚硬骨骼并且能够制造珊瑚礁的珊瑚就越少,而柔软的海鸡冠则会增加。如果酸化过于严重,珊瑚在本世纪末就有可能消失。相关论文发表在近期出版的《自然-气候变化》(Nature Climate Change)杂志上。

研究人员对冲绳县硫黄鸟岛周边海域进行了调查,这里由于火山活动而有大量二氧化碳溶解到海水中。他们同时利用水槽进行了饲养实验,确认水的酸性程度越高,珊瑚越难以生存。

研究小组发现,当海水pH值平均为8.1的时候,珊瑚生长状态最好。当pH值为7.8时,就变为以海鸡冠为主。如果pH值降至7.6以下,两者都无法生存。

天然海水的pH值稳定在7.9至8.4之间,而未受污染的海水pH值在8.0至8.3之间。海水的弱碱性有利于海洋生物利用碳酸钙形成介壳。

研究小组指出,海水pH值预计本世纪末将达7.8左右,酸度比正常状态下大幅升高,所以届时珊瑚有可能消失。

研究小组认为,海水酸化后,会溶解由碳酸钙形成的珊瑚骨骼,而珊瑚的近亲海鸡冠由于骨骼很小,且被肉质覆盖,所以抵抗海水酸化的能力较强。不过,由于海鸡冠没有珊瑚那种复杂的骨骼,很难成为各种生物的栖身之所。

了解更多:

Spatial community shift from hard to soft corals in acidified water

Nature Climate Change, 24 March 2013 | doi:10.1038/nclimate1855

Anthropogenic increases in the partial pressure of CO2 (pCO2) cause ocean acidification, declining calcium carbonate saturation states, reduced coral reef calcification and changes in the compositions of marine communities. Most projected community changes due to ocean acidification describe transitions from hard coral to non-calcifying macroalgal communities; other organisms have received less attention, despite the biotic diversity of coral reef communities. We show that the spatial distributions of both hard and soft coral communities in volcanically acidified, semi-enclosed waters off Iwotorishima Island, Japan, are related to pCO2 levels. Hard corals are restricted to non-acidified low- pCO2 (225 μatm) zones, dense populations of the soft coralSarcophyton elegans dominate medium- pCO2 (831 μatm) zones, and both hard and soft corals are absent from the highest- pCO2 (1,465 μatm) zone. In CO2-enriched culture experiments, high- pCO2conditions benefited Sarcophyton elegans by enhancing photosynthesis rates and did not affect light calcification, but dark decalcification (negative net calcification) increased with increasingpCO2. These results suggest that reef communities may shift from reef-building hard corals to non-reef-building soft corals under pCO2 levels (550–970 μatm) predicted by the end of this century, and that higher pCO2 levels would challenge the survival of some reef organisms.

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