Historical timescale records of coral growth and skeletal carbonate deposition under conditions of high turbidity and terrigenous sediment influence

人们普遍认为，珊瑚（和珊瑚礁）很容易受到陆源沉积物流入河流的影响，大量流入将对珊瑚礁的健康和活力产生不利影响（通常表现为珊瑚覆盖率低和/或部分死亡率高）。在过去这种投入有限的珊瑚礁环境中，珊瑚不适应频繁的沉积物负荷和减少的光线穿透，这种看法可能具有相当的有效性，并可能随着时间的推移导致珊瑚群落结构的变化。然而，越来越多的沉积学、地貌学和古生态学数据表明，珊瑚群落不仅在大量陆源沉积物输入和高浊度的条件下长期（超过1 000年）持续存在，而且有明显证据表明，珊瑚礁正在迅速活跃地增生。在这些条件下，珊瑚似乎充分适应了这些环境条件，珊瑚覆盖率往往很高，可以形成发育良好的珊瑚礁结构。泰国、印度尼西亚、莫桑比克以及澳大利亚大堡礁（GBR）近岸（大陆架最内侧）地区沿着的一系列地点都证明了这一点。因此，高浊度和陆源沉积物对珊瑚群落的负面影响（科学文献中广泛提到）与珊瑚和珊瑚礁在这些环境中形成的历史时间尺度持续存在的越来越多的沉积和古生态证据之间存在着明显的矛盾。这就提出了一个有趣的问题，在这些环境中的珊瑚碳酸盐生产和骨骼碳酸盐沉积的性质。这些珊瑚群落是否能够产生珊瑚礁结构，尽管高陆源沉积物输入和高浊度制度，因为特别高的珊瑚生长和钙化率？这种类型的近岸珊瑚礁的数据很少，也没有试图在时间和空间尺度上量化和比较这些过程。因此，该项目旨在量化珊瑚的扩展（生长）和钙化率，并量化微骨骼特征（即，珊瑚骨骼中关键骨骼元素的大小和密度），这两种主要珊瑚物种与大不列颠及北爱尔兰联合王国中央海岸线沿着的近岸、浑浊带环境中的造礁有关。研究的重点将是该地区研究最好的两个浊流区珊瑚礁; Paluma浅滩和Lugger浅滩。在每个地点都有关于沉积环境、水动力条件和当代群落结构的大量数据集。此外，放射性碳（14 C）日期约束的增长模型存在于每个网站，使数据被放置在一个可靠的年代框架。具体而言，我们将收集数据的一个巨大的珊瑚物种（滨珊瑚lobata），使当代礁平珊瑚群落在这两种设置的主要贡献，和分支珊瑚物种（鹿角珊瑚pulchra），以前的研究已经证明，一直是一个主要的框架贡献者在整个生长历史的这些珊瑚礁。该研究将利用新的计算机（轴向）断层扫描（CT）和已建立的扫描电子显微镜（SEM）方法来量化这些样本中珊瑚的生长速率和珊瑚骨骼沉积的风格。站点之间的比较将对收集的数据从同一物种的滨珊瑚和鹿角珊瑚，在1928年至1929年大堡礁探险期间收集的清澈的水网站在低群岛。这个广泛和分类良好的珊瑚储存库存储在NHM和CT方法将使我们能够使用非破坏性技术检查这些珊瑚的骨骼结构。

There is a general perception that corals (and coral reefs) are highly susceptible to riverine inputs of terrigenous sediment, and that high rates of such inputs will negatively impact reef health and vitality (usually evidenced by low coral cover and/or high partial mortality rates). In coral reef settings where such inputs have been limited in the past and where corals are not adapted to deal with frequent sediment loading and reduced light penetration, this perception is likely to have considerable validity and may lead, over time, to shifts in coral community structure. However, there is an increasing body of sedimentological, geomorphological and palaeoecological data demonstrating not only long-term (>1,000 year) persistence of coral communities under conditions of high terrigenous sediment input and high turbidity, but also clear evidence of active and rapid reef-accretion. Under these conditions corals seem to be sufficiently adapted to these environmental conditions that coral cover is often high and well-developed reef structures can form. This has been demonstrated at sites in Thailand, Indonesia, Mozambique and at a range of sites along the nearshore (innermost shelf) areas of the Great Barrier Reef (GBR), Australia. An apparent paradox thus exists between the perceived negative effects of high turbidity and terrigenous sediment inputs on coral communities (which are widely referred to in the scientific literature) and the increasing sedimentary and palaeoecological evidence for historical timescale persistence of corals and of reef-building in these settings. This raises an intriguing question about coral carbonate production in these environments and about the nature of skeletal carbonate deposition. Are these coral communities able to produce reef structures, despite high terrigenoclastic sediment input and high turbidity regimes, because of particularly high coral growth and calcification rates? Little data exists from nearshore reefs of this type and there has been no attempt to quantify and compare these processes over temporal and spatial scales. This project thus aims to quantify coral extension (growth) and calcification rates, and to quantify the microskeletal characteristics (i.e., the size and density of key skeletal elements in the coral skeleton) from two of the dominant coral species associated with reef-building within nearshore, turbid-zone settings along the central GBR coastline. The focus for the research will be the two best-studied turbid-zone reefs in the region; Paluma Shoals and Lugger Shoal. Extensive datasets are available on the sedimentary environments, hydrodynamic conditions and contemporary community structures in each locality. In addition, radiocarbon (14C) date-constrained growth models exist for each site that allow data to be placed in a reliable chronological framework. Specifically, we will gather data on a massive coral species (Porites lobata) that makes a major contribution to contemporary reef-flat coral communities in both settings, and a branching coral species (Acropora pulchra) which previous research has demonstrated to have been a major framework contributor throughout the growth history of these reefs. The research will utilise novel Computerised (Axial) Tomography (CT) scanning and established Scanning Electron Microscopy (SEM) approaches to quantify coral growth rates and styles of coral skeletal deposition in these samples. Between-site comparisons will be made against data collected from the same species of Porites and Acropora that were collected from clear water sites at Low Isles during the 1928-1929 Great Barrier Reef Expedition. This extensive and well-catalogued coral repository is stored at the NHM and CT methodologies will allow us to examine the skeletal structures of these corals using non-destructive techniques.