Assessing the geo-ecological consequences of the severe 2023 bleaching event on Mexican Caribbean coral reefs

评估 2023 年严重白化事件对墨西哥加勒比珊瑚礁造成的地质生态后果

• 批准号: NE/Y005546/1
• 负责人: Christopher Perry
• 金额: $ 9.4万
• 依托单位: UNIVERSITY OF EXETER
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2023
• 资助国家: 英国
• 起止时间: 2023 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FY005546%2F1
• 关键词: Assessing; geo; ecological; consequences; severe

Climate change generally, but especially the occurrence of major ocean thermal anomaly events, represents a major threat to the persistence of tropical coral reefs. This threat arises from the fact that when corals are exposed to heat stress (>1 degree C above the annual maximum) and the exposure period exceeds about 4 weeks they respond by expelling their symbiotic algae (zooxanthellae), causing them to turn completely white. If the stress event is very high and/or prolonged the corals will die. Future bleaching projections developed over the past few years have predicted the onset of high frequency bleaching events on many reefs through the next 60-80 years depending on future emission scenarios. However, over the past few months many reefs in the Caribbean have been exposed to temperatures that match these future projections in terms of magnitude and longevity - in essence providing far earlier than expected insights into the future warming regimes reefs may be increasingly exposed to.The Mexican Caribbean region has been no exception. Severe warming started in early May 2023 and measured water temperatures have exceeded 33 degrees C (3 degrees C above the normal seasonal maximum). At the time of writing (early Sept '23) the period of coral bleaching-inducing temperature exposure has already been double the maximum recorded in the region since satellite monitoring began in 1985. Widespread coral bleaching is now evident with unclear consequences for the future ecology and the persistence of reef structures in this region. However, the already very low coral cover on many Mexican Caribbean reefs leaves many reefs at a potentially critical tipping point - whereby any extirpation of what were the remaining and assumed more resilient taxa will see a widespread transition of reefs to states of net erosion over large spatial scales. The implications for the future functionality of the reefs are thus severe. We are in a unique situation to assess the impacts of this bleaching event on both the ecological attributes, but also uniquely the carbonate budget states, of the reefs in this region. Carbonate budget state data is an especially useful reef health monitoring metric from which we can quantity the capacity of reefs to sustain reef framework building and vertical reef accretion potential, functions essential to the persistence of biodiversity and reef-derived services such as coastal wave protection. Our past work, undertaken between 2017 and 2019, involved a major programme of detailed reef carbonate budget assessments at sites along the entire Mexican Mesoamerican reef system (from north of Cancun to the Belize border) and in Veracruz. We propose to undertake a full re-assessment of these sites to provide the most comprehensive reef-tract scale data on the impacts of bleaching that will allow us: 1) to quantify the nature and magnitude of change in coral assemblages at each site, including identification of any between-site variations in species susceptibility; 2) to quantify the magnitude of change in rates of reef carbonate production and bioerosion, and to discern the extent to which taxa are still contributing to the production versus erosion balance; and 3) to quantify the impacts on the vertical accretion potential of these reefs.

一般来说，气候变化，特别是重大海洋热异常事件的发生，是热带珊瑚礁持续存在的主要威胁。这种威胁来自于这样一个事实，即当珊瑚暴露在热应激下（比年最高温度高出10摄氏度），并且暴露期超过4周时，它们会排出共生藻类（虫黄藻），导致它们完全变白。如果压力过大和/或持续时间过长，珊瑚就会死亡。根据未来的排放情景，过去几年发展起来的未来白化预测预测了未来60-80年许多珊瑚礁发生高频白化事件的可能性。然而，在过去的几个月里，加勒比地区的许多珊瑚礁已经暴露在与这些未来预测相匹配的温度下，就规模和寿命而言，这实际上比预期的更早地提供了对未来珊瑚礁可能日益暴露的变暖机制的见解。墨西哥加勒比地区也不例外。2023年5月初开始严重变暖，测得的水温已超过33摄氏度（比正常的季节性最高温度高3摄氏度）。在撰写本文时（9月23日上旬），导致珊瑚白化的温度暴露期已经是该地区自1985年开始卫星监测以来记录的最大值的两倍。广泛的珊瑚白化现在很明显，对该地区未来的生态和珊瑚礁结构的持久性造成了不清楚的后果。然而，在墨西哥加勒比海的许多珊瑚礁上，已经非常低的珊瑚覆盖率使许多珊瑚礁处于潜在的关键临界点——由此，任何剩余的和假定的更有弹性的分类群的灭绝都将导致珊瑚礁在大空间尺度上向净侵蚀状态的广泛过渡。因此，这对珊瑚礁未来功能的影响是严重的。我们正处于一个独特的情况下，以评估这种漂白事件对生态属性的影响，但也独特的碳酸盐收支状态，在这个地区的珊瑚礁。碳酸盐预算状态数据是一个特别有用的珊瑚礁健康监测指标，从中我们可以量化珊瑚礁维持珊瑚礁框架建设和垂直珊瑚礁增生潜力的能力，这些功能对生物多样性的持久性和珊瑚礁衍生服务（如海岸波浪保护）至关重要。我们过去的工作是在2017年至2019年之间进行的，涉及在整个墨西哥中美洲珊瑚礁系统（从坎昆北部到伯利兹边境）和韦拉克鲁斯的遗址进行详细的珊瑚礁碳酸盐预算评估的主要项目。我们建议对这些地点进行全面的重新评估，以提供有关白化影响的最全面的珊瑚礁尺度数据，使我们能够：1)量化每个地点珊瑚组合变化的性质和幅度，包括确定物种易感性在地点之间的任何变化；2)量化珊瑚礁碳酸盐生成速率和生物侵蚀速率的变化幅度，并辨别哪些分类群仍在促进生成与侵蚀平衡；3)量化对这些珊瑚礁垂直增长潜力的影响。