Quantifying ENSO-related bleaching on nearshore, turbid-zone coral reefs: a test of the turbid-zone reef climate change refugia hypothesis.

在过去的两个月里，越来越多的报道称，当前的厄尔尼诺现象导致了澳大利亚大堡礁(GBR)沿线的大规模珊瑚白化，航空调查显示，90%的珊瑚礁正在白化，这些珊瑚礁上超过50%的珊瑚已经死亡。然而，这些调查无法评估近岸浑浊带珊瑚礁上正在发生的事情，首先是因为浑浊程度阻碍了空中评估，其次是因为几乎没有生态数据可以比较变化。然而，珊瑚在这些浑浊带珊瑚礁上的漂白反应具有重大的科学意义。这种兴趣特别涉及这样一种假设，即可能有特定的海洋环境可以作为防止漂白的重要避难所，即更有效地缓冲表面变暖的环境，使珊瑚种群基本上不受影响。在冲洗良好、高度浑浊的环境中形成的珊瑚礁是这些避难所的候选地点之一。漂白能力增强的假设是因为水中的高颗粒物含量可能会限制紫外线胁迫，而且因为珊瑚可能更容易切换到主要的异养摄食模式-这是增强对热应激事件的保护的原因，这些最初在2000年初被假设为S。然而，最近的模拟现在提供了一个全球尺度的框架，通过它可以定义这种潜在避难所的空间范围。然而，缺乏的是明确表明这些浑浊带珊瑚礁实际上能够经受住重大珊瑚白化事件的任何经验现场证据。毫无疑问，在这些混浊地带的珊瑚礁中，研究最好的是沿GBR近岸地区的珊瑚礁，自2006年以来，这些珊瑚礁一直是PI及其小组密集研究的重点。这项工作主要侧重于评估珊瑚礁的生长速度和类型，但我们最近的工作的中心目标是评估这些珊瑚礁的空间范围和当代生态结构。我们在GBR中部开展了一场史无前例的测绘和生态调查活动，收集了130公里的海底条带调查数据和4,500个视频静止样机。由此产生的数据集使我们能够开发出高分辨率的珊瑚礁结构和生态组成地图，这些地图显示，尽管这些珊瑚礁的水深范围很窄，但具有明显的深度控制的生态分区的特征，并且它们显示出高活珊瑚覆盖率(平均：38%，但高达~80%)。因此，我们处于一个独特的位置，可以定量地评估这一重大漂白事件对这些浑浊带珊瑚礁的影响程度，并检验最近提出的假设，即这些珊瑚礁可能是关键的气候变化避难所。在这个项目中，我们将对白化对Paluma Shoals(哈利法克斯湾中部)附近的浑浊带珊瑚礁的影响进行快速评估。我们将使用远程操作的水下视频调查方法重新检查一套六个近端珊瑚礁，并收集每个珊瑚礁重复横断面上的生态数据。视频数据将用于确定物种丰度和漂白强度。这将使我们能够确定：1)漂白引起的死亡的总程度；2)特定珊瑚物种受到影响的程度；以及3)对珊瑚礁结构复杂性和多样性的任何直接影响。我们还将对其他混浊地带的珊瑚礁进行类似的评估，这些珊瑚礁是我们早先研究的重点，例如再往北靠近丹克岛，再往南到中礁--这些珊瑚礁的地貌和沉积环境与帕鲁马建筑群相似。因此，这项工作不仅将提供关于浑浊带珊瑚礁漂白程度的数据，还将对浑浊带珊瑚礁可能形成关键的气候变化避难所这一假设进行有力的检验。

Over the last two months there have been increasing reports of the current El Niño causing massive coral bleaching along Australia's Great Barrier Reef (GBR), with aerial surveys reporting that >90% of reefs are bleaching, and with more that 50% of corals on these reefs already dead. However, these surveys cannot assess what is happening on the nearshore turbid-zone reefs, firstly because turbidity levels inhibit aerial assessments, and secondly because there is little ecological data against which to compare change. The bleaching response of corals on these turbid-zone reefs is however of significant scientific interest. This interest relates specifically to the hypothesis that there may be particular marine environments that might act as important refugia sites from bleaching i.e., settings that are more effectively buffered from surface warming such that coral populations remain largely unaffected. Reefs forming in well-flushed, highly turbid settings are one such candidate location for these refugia. Increased bleaching resilience has been hypothesized because high particulate content in the water may limit UV stress, and because the corals may be more readily able to switch to predominantly heterotrophic feeding modes - reasons for enhanced protection from thermal stress events that were initially hypothesised in the early 2000's. However, recent modelling now provides a global-scale framework through which the spatial extent of such potential refugia can be defined. What is lacking however is any empirical field evidence definitively showing that these turbid-zone reefs are actually able to withstand major coral bleaching events. Without doubt the best studied of these turbid-zone reefs are those along the nearshore areas of the GBR, which have been the focus of intensive study by the PI and his group since 2006. This work has largely focused on assessing rates and styles of reef growth, but our most recent work has had as its central aim an assessment of the spatial extent and contemporary ecological structure of these reefs. Working at sites in the central GBR we have undertaken an unprecedented mapping and ecological surveying campaign, collecting >130 km of seafloor swath survey data and >4,500 video still quadrats. The resulting datasets have enabled us to develop high resolution maps of reef structure and ecological composition, which show that despite their narrow bathymetric extent, these reefs are characterised by a clear depth-controlled ecological zonation, and that they exhibit high live coral cover (mean: 38%, but up to ~80%). We are thus in a unique position to quantitatively assess the extent to which this major bleaching event has impacted these turbid-zone reefs, and to test the recently proposed hypothesis that such reefs may act as critical climate change refugia sites.In this project we will undertake a rapid assessment of the impacts of bleaching on the turbid-zone reefs in the vicinity of Paluma Shoals (central Halifax Bay). We will re-examine a suite of six proximal reefs using remotely-operated underwater video survey methods and collect ecological data along replicate transects across each reef. Video data will be used to determine species abundance and bleaching intensity. This will allow us to ascertain: 1) the total extent of bleaching-induced mortality; 2) the extent to which specific coral species have been impacted; and 3) any immediate impacts on the structural complexity and diversity of the reefs. We will also undertake comparable assessments at other turbid-zone reefs which have been the focus of our earlier studies e.g., further north around Dunk Island and to the south at Middle Reef- these reefs occupying similar geomorphic and sedimentary settings to the Paluma complex. The work would thus deliver not only data on the extent of turbid-zone reef bleaching, but also provide a robust test of the hypothesis that turbid-zone reefs may form critical climate change refugia sites.