Photosynthetic rates verses growth rates of Acropora millepora at Lizard and Heron Island (MTSRF 2.5i.2, UQ)

The aim of this component of the study was to determine how photosynthetic rates related to growth rates both into terms of skeletal deposition and organic carbon accrual associated with linear extension, and with organic carbon accrual associated with fat deposition or lipid enrichment of existent tissue. The study was based on the coral Acropora millepora located at Lizard Island (-14°40’, 145°27’) and at Heron Island (-23°26', 151°54') in the Great Barrier Reef (GBR) of Australia, with data collected for winter and summer months.

Coral colonies were monitored for two years, with both summers breaching maximum mean monthly maximum sea surface temperatures, but by less than the NOAA Bleach Watch trigger of 1°C, Lizard Island colonies proved to be highly susceptible to whole colony mortality, with a loss of 2 of 5 colonies monitored. Heron Island colonies proved to be more robust with no whole colony mortality. Interestingly, comparisons of the growth rate of Lizard colonies in summer to that of Heron colonies in winter showed that despite winter heterotrophy in Heron colonies, compared to summer autotrophy in Lizard colonies: Corals had greater linear extension in the winter at Heron, than they did in the summer at Lizard. Heron and Lizard colonies at these times were equally fat with non-significant differences in lipid per surface area. Heron colonies appear to maintain their weight (areal lipid concentrations) and growth (positive linear extension) despite a potential reliance on heterotrophy, whilst Lizard colonies appear to struggle despite high rates of photosynthesis. The study therefore reinforces the notion that projections regarding coral health need to greater appreciate the mixotrophic lifestyle of corals.

The following parameters were measured:
Temperature in degrees C;
Pnet max as micromol O2 h-1 cm-2;
Lipid per surface area as mass per cm-2;

本研究子项的核心目标为明确光合速率与生长速率的关联模式，其中生长速率既涵盖与线性延伸相关的骨骼沉积与有机碳积累过程，也涉及现存组织脂肪沉积或脂质富集所伴随的有机碳积累过程。本研究以澳大利亚大堡礁（Great Barrier Reef, GBR）蜥蜴岛（Lizard Island，坐标-14°40′，145°27′）与赫伦岛（Heron Island，坐标-23°26′，151°54′）的千孔鹿角珊瑚（Acropora millepora）为实验材料，于冬季与夏季两季采集相关数据。

珊瑚群落被连续监测两年，两年夏季的月均海表最高温度均突破历史极值，但升温幅度未达到美国国家海洋和大气管理局（National Oceanic and Atmospheric Administration, NOAA）漂白预警触发阈值1℃。其中，蜥蜴岛的珊瑚群落极易发生全群落死亡，监测的5个群落中共有2个完全损失；而赫伦岛的珊瑚群落耐受性更强，未出现全群落死亡案例。值得注意的是，对比蜥蜴岛夏季与赫伦岛冬季的珊瑚生长速率可发现：尽管赫伦岛珊瑚在冬季依赖异养代谢，而蜥蜴岛珊瑚在夏季依赖自养代谢，但赫伦岛冬季珊瑚的线性延伸速率显著高于蜥蜴岛夏季的珊瑚。在该对比时段内，两地珊瑚的脂肪含量相当，单位表面积脂质含量无统计学显著性差异。尽管赫伦岛珊瑚可能依赖异养获取营养，但其仍能维持体重（单位面积脂质浓度）与生长水平（正向线性延伸）；而蜥蜴岛珊瑚即便拥有较高的光合速率，却仍出现生长受限的情况。因此，本研究进一步佐证了这一观点：珊瑚健康预测需更加重视珊瑚的混养生活策略。

本研究测定的参数如下：
1. 温度，单位：摄氏度（℃）；
2. 最大净光合速率（Pnet max），单位：微摩尔氧气每小时每平方厘米（μmol O₂ h⁻¹ cm⁻²）；
3. 单位表面积脂质含量，单位：质量每平方厘米（mass per cm⁻²）。