Classification of coral reef types in Torres Strait (GIS files in zip-archive 319 kB)

Coral reefs represent major accumulations of calcium carbonate (CaCO3). The particularly labyrinthine network of reefs in Torres Strait, north of the Great Barrier Reef (GBR), has been examined in order to estimate their gross CaCO3 productivity. The approach involved a two-step procedure, first characterising and classifying the morphology of reefs based on a classification scheme widely employed on the GBR and then estimating gross CaCO3 productivity rates across the region using a regional census-based approach. This was undertaken by independently verifying published rates of coral reef community gross production for use in Torres Strait, based on site-specific ecological and morphological data. A total of 606 reef platforms were mapped and classified using classification trees. Despite the complexity of the maze of reefs in Torres Strait, there are broad morphological similarities with reefs in the GBR. The spatial distribution and dimensions of reef types across both regions are underpinned by similar geological processes, sea-level history in the Holocene and exposure to the same wind/wave energetic regime, resulting in comparable geomorphic zonation. However, the presence of strong tidal currents flowing through Torres Strait and the relatively shallow and narrow dimensions of the shelf exert a control on local morphology and spatial distribution of the reef platforms. A total amount of 8.7 million tonnes of CaCO3 per year, at an average rate of 3.7 kg CaCO3 m-2 yr-1 (G), were estimated for the studied area. Extrapolated production rates based on detailed and regional census-based approaches for geomorphic zones across Torres Strait were comparable to those reported elsewhere, particularly values for the GBR based on alkalinity-reduction methods. However, differences in mapping methodologies and the impact of reduced calcification due to global trends in coral reef ecological decline and changing oceanic physical conditions warrant further research. The novel method proposed in this study to characterise the geomorphology of reef types based on classification trees provides an objective and repeatable data-driven approach that combined with regional census-based approaches has the potential to be adapted and transferred to different coral reef regions, depicting a more accurate picture of interactions between reef ecology and geomorphology.

珊瑚礁是碳酸钙（calcium carbonate, CaCO₃）的主要堆积体。位于大堡礁（Great Barrier Reef, GBR）北侧的托雷斯海峡内，其异常蜿蜒复杂的礁体网格已被纳入研究，以估算该区域的碳酸钙总生产力。
本次研究采用两步法流程：首先基于大堡礁广泛使用的分类方案，对礁体形态进行表征与分类；随后采用基于区域普查的方法，估算整片区域的碳酸钙总生产力速率。该流程通过针对托雷斯海峡的特定场地生态与形态数据，独立验证已发表的珊瑚礁群落总生产力速率，以适配本区域的研究需求。
研究共测绘并分类了606个礁台，所用方法为分类树（classification trees）。尽管托雷斯海峡的礁体迷宫结构复杂，但其与大堡礁的礁体存在广泛的形态相似性。两个区域内各类礁体的空间分布与规模，均受相似的地质作用、全新世海平面演化历史以及相同的风浪动力环境调控，因此形成了具有可比性的地貌分带特征。然而，流经托雷斯海峡的强劲潮流，以及该陆架相对浅窄的展布特征，对礁台的局部形态与空间分布施加了独特的调控作用。
研究估算得到，研究区域的年碳酸钙总产量约为870万吨，平均速率为3.7 kg CaCO₃·m⁻²·yr⁻¹（G）。基于托雷斯海峡各地貌区的详细区域普查方法得到的外推生产力速率，与其他区域的报道值相当，尤其是基于碱度降低法得到的大堡礁相关数值。但制图方法的差异，以及全球珊瑚礁生态衰退与海洋物理条件变化所导致的钙化作用减弱的影响，仍有待进一步研究。
本研究提出的基于分类树的礁体类型地貌表征新方法，提供了一种客观且可重复的数据驱动研究路径。该方法结合基于区域普查的分析手段，具备被适配并迁移至不同珊瑚礁区域的潜力，可更精准地刻画礁体生态与地貌之间的相互作用。