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Oceanic patterns of thermal stress and coral community degradation on the island of Mauritius
Coral Reefs ( IF 3.5 ) Pub Date : 2020-10-31 , DOI: 10.1007/s00338-020-02015-4
T. R. McClanahan , Nyawira A. Muthiga

Knowing the responses of high-latitude corals to thermal impacts will be critical to predicting the possibility for range expansion of reefs provoked by climate change. We, therefore, tested how oceanographic and island geography variation and subsequent interactions between chronic and acute environmental stresses would influence the temperate corals of Mauritius (~ 20°S). Specifically, we predicted higher impacts of thermal stress due to rare events on ocean-impacted windward than leeward reefs. To test this prediction, surveys of benthic cover and corals in the shallow lagoon’s perimeter reefs were repeated between 2004 and 2019—an interval with frequent warm thermal anomalies. Hard and soft coral cover declined 40% and 83%, respectively, and erect algae increased 78% over the 15-yr interval. Coral taxa were distributed along a Montipora -community axis dominant on the island’s leeward reefs and an Acropora -axis dominant on the windward reefs. Nine of the 30 originally encountered sub-genera were not observed in the second sampling, of which most losses were on the windward reefs and among taxa that were initially uncommon during the initial 2004 sampling. The largest declines occurred in the southeast where rare acute stress was higher and open-ocean conditions interacted strongly with the island. The north and western corals experienced less acute stress and greater persistence of taxa. Searching an additional 15 sites in 2019 found six of the missing coral taxa, often in deeper reef edges. Screening of potential environmental variables indicated that that skewness of the degree heating weeks and thermal stress anomalies were the strongest predictor of the changes. A chronic stress metric was more difficult to identify but water flow variability and chlorophyll-a concentrations were part of the oceanographic conditions associated with attenuated responses to acute stress. Frequent acute stress was associated with lower thermal acclimation rates over the 15-yr interval and more evident for the dominant than subdominant taxa. The extra-equatorial location of Mauritius will not ensure latitudinal sanctuary, apart from the leeward reefs.

中文翻译:

毛里求斯岛上热应力和珊瑚群落退化的海洋模式

了解高纬度珊瑚对热影响的反应对于预测气候变化引起的珊瑚礁范围扩大的可能性至关重要。因此,我们测试了海洋和岛屿地理变化以及慢性和急性环境压力之间随后的相互作用将如何影响毛里求斯的温带珊瑚(~ 20°S)。具体而言,我们预测,由于罕见事件对受海洋影响的迎风礁造成的热应力影响高于背风礁。为了验证这一预测,在 2004 年至 2019 年间重复了对浅水泻湖周边珊瑚礁中的底栖覆盖物和珊瑚的调查——这是一个频繁出现暖热异常的区间。在 15 年的时间间隔内,硬珊瑚和软珊瑚的覆盖率分别下降了 40% 和 83%,直立藻类增加了 78%。珊瑚分类群沿着在岛屿背风礁上占优势的蒙蒂波拉群落轴和在迎风礁上占优势的鹿角群轴分布。在第二次采样中没有观察到最初遇到的 30 个亚属中的 9 个,其中大部分损失发生在迎风礁和在 2004 年最初采样期间最初不常见的分类群中。最大的下降发生在东南部,那里罕见的急性压力更高,开阔的海洋条件与该岛相互作用强烈。北部和西部珊瑚经历了较少的急性压力和更大的分类群持久性。2019 年又搜索了 15 个地点,发现了六个缺失的珊瑚分类群,通常位于更深的珊瑚礁边缘。潜在环境变量的筛选表明,加热周的偏度和热应力异常是变化的最强预测因子。慢性压力指标更难确定,但水流变异性和叶绿素-a 浓度是与对急性压力的减弱反应相关的海洋条件的一部分。频繁的急性应激与 15 年间隔内较低的热适应率有关,并且优势类群比次优势类群更明显。除了背风礁外,毛里求斯的赤道外位置不会确保纬度保护区。慢性压力指标更难确定,但水流变异性和叶绿素-a 浓度是与对急性压力的减弱反应相关的海洋条件的一部分。频繁的急性应激与 15 年间隔内较低的热适应率有关,并且优势类群比次优势类群更明显。除了背风礁外,毛里求斯的赤道外位置不会确保纬度保护区。慢性压力指标更难确定,但水流变异性和叶绿素-a 浓度是与对急性压力的减弱反应相关的海洋条件的一部分。频繁的急性应激与 15 年间隔内较低的热适应率有关,并且优势类群比次优势类群更明显。除了背风礁外,毛里求斯的赤道外位置不会确保纬度保护区。
更新日期:2020-10-31
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