Oceans Institute and School of Earth Sciences, The University of Western Australia, 35 Stirling Hwy, Crawley WA 6009, Australia
ARC Centre of Excellence for Coral Reef Studies, The University of Western Australia, 35 Stirling Hwy, Crawley WA 6009, Australia.
Proc Biol Sci. 2018 May 30;285(1879). doi: 10.1098/rspb.2018.0215.
High-latitude coral reefs provide natural laboratories for investigating the mechanisms and limits of coral calcification. While the calcification processes of tropical corals have been studied intensively, little is known about how their temperate counterparts grow under much lower temperature and light conditions. Here, we report the results of a long-term (2-year) study of seasonal changes in calcification rates, photo-physiology and calcifying fluid (cf) chemistry (using boron isotope systematics and Raman spectroscopy) for the coral growing near its latitudinal limits (34.5° S) along the southern coast of Western Australia. In contrast with tropical corals, calcification rates were found to be threefold higher during winter (16 to 17° C) compared with summer (approx. 21° C), and negatively correlated with light, but lacking any correlation with temperature. These unexpected findings are attributed to a combination of higher chlorophyll a, and hence increased heterotrophy during winter compared with summer, together with the corals' ability to seasonally modulate pH, with carbonate ion concentration [Formula: see text] being the main controller of calcification rates. Conversely, calcium ion concentration [Ca] declined with increasing calcification rates, resulting in aragonite saturation states that were stable yet elevated fourfold above seawater values. Our results show that corals growing near their latitudinal limits exert strong physiological control over their cf in order to maintain year-round calcification rates that are insensitive to the unfavourable temperature regimes typical of high-latitude reefs.
高纬度珊瑚礁为研究珊瑚钙化的机制和限制提供了天然实验室。虽然热带珊瑚的钙化过程已得到深入研究，但对于其温带同类在温度和光照条件低得多的情况下如何生长，人们知之甚少。在这里，我们报告了对澳大利亚西部南部海岸生长的珊瑚在其纬度极限附近（34.5°S）进行的为期 2 年的钙化率、光生理和钙化液（cf）化学季节性变化的长期研究结果（使用硼同位素系统和拉曼光谱）。与热带珊瑚不同，我们发现钙化率在冬季（16 至 17°C）比夏季（约 21°C）高三倍，与光照呈负相关，但与温度无关。这些出乎意料的发现归因于冬季比夏季叶绿素 a 更高，因此异养作用增加，以及珊瑚季节性调节 pH 值的能力，其中碳酸盐离子浓度 [Formula: see text] 是控制钙化率的主要因素。相反，钙离子浓度 [Ca] 随着钙化率的增加而下降，导致文石饱和度稳定，但比海水值高四倍。我们的研究结果表明，在其纬度极限附近生长的珊瑚对其 cf 施加了强烈的生理控制，以维持全年不受高纬度珊瑚礁典型不利温度条件影响的钙化率。
