The global pattern of marine biodiversity is primarily constructed based on information from extra-tropical sites. A severe knowledge gap in the shallow benthic diversity exists for the tropical Indian Ocean, especially along the coastline of peninsular India. Latitudinal biodiversity gradient (LBG) – a poleward decrease in diversity, even though accepted as a pervasive global pattern, often differs from regional trends. Although several oceanographic variables are known to influence regional patterns, their relative effect in shaping the shallow benthic community in tropical seas remains unclear. The east coast of India bordering the Bay of Bengal (BoB) presents a 2500 km stretch (8°N - 21°N) of tropical coastline with a spatial variation in oceanographic parameters including freshwater mixing, primary productivity, temperature, shelf area. Here, we documented the marine bivalve distribution using spatially-temporally averaged beach samples and evaluated their relationship with the oceanographic variables. Our data reveal the existence of a highly diverse fauna, comparable to other tropical shallow marine sites. The overall species composition reflects a typical assemblage of Indian Ocean, dominated by Veneridae but shows uncharacteristically low proportion of Tellinidae and Lucinidae. The latitudinal variation in diversity shows a mid-latitude peak at around 14°N, decreasing symmetrically – a pattern inconsistent with the prediction of LBG. The ecology is dominated by infauna (65%), unattached groups (69%) and suspension feeders (87%). There is no strong compositional dissimilarity between southern and the northern sites pointing to a predominantly continuous circulation and considerable mixing within the BoB. Productivity range and shelf width emerge as best predictors of the species richness. Along with these, salinity range contributes significantly in determining the ecology and shaping the species composition. The species composition of the east coast shows no distinct endemism in comparison to Indo-Malayan biodiversity hotspot; the close proximity to this hotspot and biological exchange with it may have contributed to the high diversity of the east coast fauna. Our study highlights the complex interplay between multiple oceanographic variables in determining the distribution and diversity of tropical shallow marine benthos at regional scale generating regional biodiversity patterns that are in odds with global trends such as LBG.

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孟加拉湾沿印度东海岸的海洋双壳类动物的分布及其海洋学决定因素

海洋生物多样性的全球格局主要是根据来自温带地区的信息构建的。对于热带印度洋，特别是在印度半岛的海岸线上，浅层底栖生物多样性存在严重的知识鸿沟。纬度生物多样性梯度（LBG）–多样性呈极度下降的趋势，尽管被认为是普遍存在的全球格局，但通常与区域趋势有所不同。尽管已知一些海洋变量会影响区域格局，但它们在塑造热带海洋浅层底栖生物群落方面的相对作用仍不清楚。印度东部海岸与孟加拉湾（BoB）接壤，绵延2500公里（8°N-21°N），热带海岸带海洋学参数具有空间变化，包括淡水混合，初级生产力，温度，架子面积。这里，我们使用时空平均海滩样本记录了海洋双壳类动物的分布，并评估了它们与海洋变量的关系。我们的数据揭示了存在高度多样性的动物群，可与其他热带浅海站点相媲美。总体物种组成反映了印度洋的一种典型组合，其中以Ven科（Veneridae）为主导，但其Tell兰科（Tellinidae）和露尾科（Lucinidae）的比例却异常低。多样性的纬度变化在14°N附近显示了一个中纬度峰，对称地下降-这种模式与LBG的预测不一致。生态环境主要由不育系（65％），独立的群体（69％）和悬浮饲养者（87％）主导。在南部和北部站点之间没有强烈的成分差异，表明BoB内部主要是连续的循环和大量的混合。生产力范围和架子宽度成为物种丰富度的最佳预测指标。除此以外，盐度范围在确定生态学和塑造物种组成方面也起着重要作用。与印度马来亚生物多样性热点相比，东海岸的物种组成没有明显的地方性。靠近该热点并与之进行生物交换可能导致了东海岸动物区系的高度多样性。