Effects of light and elevated pCO2 on the growth and photochemical efficiency of Acropora cervicornis

The effects of light and elevated pCO2 on the growth and photochemical efficiency of the critically endangered staghorn coral, Acropora cervicornis, were examined experimentally. Corals were subjected to high and low treatments of CO2 and light in a fully crossed design and monitored using 3D scanning and buoyant weight methodologies. Calcification rates, linear extension, as well as colony surface area and volume of A. cervicornis were highly dependent on light intensity. At pCO2 levels projected to occur by the end of the century from ocean acidification (OA), A. cervicornis exhibited depressed calcification, but no change in linear extension. Photochemical efficiency (F v /F m ) was higher at low light, but unaffected by CO2. Amelioration of OA-depressed calcification under high-light treatments was not observed, and we suggest that the high-light intensity necessary to reach saturation of photosynthesis and calcification in A. cervicornis may limit the effectiveness of this potentially protective mechanism in this species. High CO2 causes depressed skeletal density, but not linear extension, illustrating that the measurement of extension by itself is inadequate to detect CO2 impacts. The skeletal integrity of A. cervicornis will be impaired by OA, which may further reduce the resilience of the already diminished populations of this endangered species.本实验探究了光照与升高的二氧化碳分压（pCO₂）对极危物种鹿角轴孔珊瑚（Acropora cervicornis）的生长及光化学效率的影响。实验采用完全交叉设计设置CO₂与光照的高低梯度处理组，并通过三维扫描与浮力称重法对珊瑚样本进行监测。 鹿角轴孔珊瑚的钙化速率、线性延伸率以及群体表面积与体积均高度依赖光照强度。在本世纪末因海洋酸化（Ocean Acidification, OA）预估达到的pCO₂水平下，该珊瑚的钙化作用受到抑制，但线性延伸率未发生显著变化。光化学效率（F_v/F_m）在低光照条件下更高，但不受CO₂浓度影响。 本研究未观测到高光照处理可缓解海洋酸化所抑制的钙化作用；分析认为，鹿角轴孔珊瑚达到光合作用与钙化饱和所需的高光照强度，可能限制了该潜在保护机制在该物种中的有效性。高CO₂浓度会降低珊瑚骨骼密度，但不会影响其线性延伸率，这表明仅通过延伸率的测量无法全面检测CO₂的影响。海洋酸化将损害鹿角轴孔珊瑚的骨骼完整性，可能进一步削弱本已种群数量锐减的该濒危物种的恢复能力。