Seawater carbonate chemistry, calcification rate, oxygen production, maximum quantum yield, symbiont density, chlorophyll concentration and crystal width of Halimeda macroloba, Halimeda cylindracea and Marginopora vertebralis during experiments, 2011

The effects of elevated CO2 and temperature on photosynthesis and calcification in the calcifying algae Halimeda macroloba and Halimeda cylindracea and the symbiont-bearing benthic foraminifera Marginopora vertebralis were investigated through exposure to a combination of four temperatures (28°C, 30°C, 32°C, and 34°C) and four CO2 levels (39, 61, 101, and 203 Pa; pH 8.1, 7.9, 7.7, and 7.4, respectively). Elevated CO2 caused a profound decline in photosynthetic efficiency (FV : FM), calcification, and growth in all species. After five weeks at 34°C under all CO2 levels, all species died. Chlorophyll (Chl) a and b concentration in Halimeda spp. significantly decreased in 203 Pa, 32°C and 34°C treatments, but Chl a and Chl c2 concentration in M. vertebralis was not affected by temperature alone, with significant declines in the 61, 101, and 203 Pa treatments at 28°C. Significant decreases in FV : FM in all species were found after 5 weeks of exposure to elevated CO2 (203 Pa in all temperature treatments) and temperature (32°C and 34°C in all pH treatments). The rate of oxygen production declined at 61, 101, and 203 Pa in all temperature treatments for all species. The elevated CO2 and temperature treatments greatly reduced calcification (growth and crystal size) in M. vertebralis and, to a lesser extent, in Halimeda spp. These findings indicate that 32°C and 101 Pa CO2, are the upper limits for survival of these species on Heron Island reef, and we conclude that these species will be highly vulnerable to the predicted future climate change scenarios of elevated temperature and ocean acidification.本研究通过设置4个温度梯度（28℃、30℃、32℃、34℃）与4个CO₂浓度梯度（39、61、101、203 Pa；对应pH分别为8.1、7.9、7.7、7.4）的复合处理，探究了高CO₂浓度与升温对钙化藻类大叶仙掌藻（Halimeda macroloba）、圆柱仙掌藻（Halimeda cylindracea）以及携共生底栖有孔虫脊椎边球虫（Marginopora vertebralis）的光合作用与钙化作用的影响。高CO₂浓度显著降低了所有受试物种的光合效率（Fᵥ:Fₘ）、钙化作用与生长速率。在所有CO₂浓度处理下，于34℃培养5周后，所有受试物种均死亡。仙掌藻属（Halimeda spp.）的叶绿素a、b含量在203 Pa、32℃及34℃处理组中显著下降；而脊椎边球虫的叶绿素a与叶绿素c₂含量仅不受单一温度变化影响，但在28℃条件下，61、101及203 Pa的CO₂处理会使其含量显著降低。所有受试物种在暴露于高CO₂浓度（所有温度处理下的203 Pa组）与升温（所有pH处理下的32℃、34℃组）5周后，其光合效率（Fᵥ:Fₘ）均出现显著下降。所有受试物种在所有温度处理下，于61、101及203 Pa的CO₂处理组中，产氧速率均出现下降。高CO₂与升温处理显著降低了脊椎边球虫的钙化作用（包括生长与晶体尺寸），对仙掌藻属物种的影响相对较弱。本研究结果表明，32℃与101 Pa的CO₂浓度是这些物种在赫伦岛礁（Heron Island reef）生存的上限阈值；综上，这些物种极易受到未来预估的升温与海洋酸化气候变化情景的影响。