Interactive effects of climate change and eutrophication on the dinoflagellate-bearing benthic foraminifer Marginopora vertebralis
Interactive effects of climate change and eutrophication on the dinoflagellate-bearing benthic foraminifer Marginopora vertebralis
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气候变化和富营养化对携带甲藻的底栖有孔虫 Marginopora vertebralis 的交互影响
作者：
S. Uthicke;N. Vogel;Jason Doyle;Christiane Schmidt;C. Humphrey
全球气候变化导致的海面温度升高和陆地径流导致的营养浓度增加都是珊瑚礁生物钙化的压力源。在这里，我们测试了这样一个假设：温度升高会导致类似于珊瑚的甲藻有孔虫白化，并且通过径流增加的营养物质会加剧对全生物的压力。在一项单独控制温度的实验中，我们发现椎缘孔菌的死亡率随着温度的升高而增加。大多数个体在 34°C（比当前夏季最高温度高出约 5°C）的温度下 7 天后死亡。 28°C 时 37 天的存活率 >98%。暴露于 31 或 32°C 7 天后，内共生体的光合作用受到损害，如几个光生理参数（有效量子产率和表观光合速率）所示。在操纵温度（三个水平，26、29 和 31°C）和硝酸盐浓度（三个水平，~0.5、1.0 和 1.4 μmol l−1 NO3−）的流通实验中，升高的温度对大多数测量参数有显着的负面影响。在 31°C 时，有孔虫中的大多数感光色素（通过 UPLC 测量）显着减少。唯一增加的色素是具有光保护作用的二毒黄素。测量的其他几个参数（最大和有效量子产率、光下氧气产量、有机碳含量）也随着温度的升高而显着降低。基于光极的呼吸测量法表明，高温下共生体的存在代表了宿主的净碳损失。实验结束时椎骨支原体的生长率和死亡率受到温度升高和硝酸盐添加的显着影响。我们的结论是，这些有孔虫以与珊瑚类似的方式漂白，全球海面温度变化和硝酸盐增加对这些原生生物来说是压力源。此外，这支持了这样的假设：对局部压力源的管理可以提高珊瑚礁对全球压力源的恢复能力。
Elevated sea surface temperatures caused by global climate change and increased nutrient concentrations resulting from land runoff both are stressors for calcifying coral reef organisms. Here, we test the hypothesis that increased temperature leads to bleaching in dinoflagellate-bearing foraminifera similar to corals and that increased nutrients through runoff can exaggerate stress on the holobiont. In an experiment manipulating temperatures alone, we have shown that mortality of Marginopora vertebralis increased with temperatures. Most individuals died after 7 days at 34°C, ~5°C above current summer maxima. Survival at 37 days was >98% at 28°C. After 7 days of exposure to 31 or 32°C, photosynthesis of the endosymbionts was compromised, as indicated by several photophysiological parameters (effective quantum yield and apparent photosynthetic rate). In a flow-though experiment manipulating both temperature (three levels, 26, 29 and 31°C) and nitrate concentrations (3 levels, ~0.5, 1.0 and 1.4 μmol l−1 NO3−), elevated temperature had a significant negative effect on most parameters measured. At 31°C, most photopigments (measured by UPLC) in the foraminifera were significantly reduced. The only pigment that increased was the photoprotective diatoxanthin. Several other parameters measured (maximum and effective quantum yield, O2 production in light, organic carbon contents) also significantly decreased with temperature. Optode-based respirometry demonstrated that the presence of symbionts at elevated temperatures represents a net carbon loss for the host. Growth rates of M. vertebralis and mortality at the end of the experiment were significantly affected by both temperature increase and nitrate addition. We conclude that these foraminifera bleach in a similar fashion to corals and that global sea surface temperature change and nitrate increases are stressors for these protists. Furthermore, this provides support for the hypothesis that management of local stressors elevates resilience of coral reefs to global stressors.