Global warming is leading to range shifts of marine species, threatening the structure and functioning of ecological communities and human populations that rely on them. The largest changes are seen in biogeographic transition zones, such as subtropical reef communities, where species range shifts are already causing substantial community reorganisation. This causes functional changes in communities over subtropical latitudes, though a baseline functional understanding remains elusive for many taxa. One key marine taxon are molluscs, which provide many ecosystem services, are important prey for fishes and are also fisheries targets themselves, but remain largely unstudied. Here, we examine the trait composition, functional diversity, and functional redundancy of mollusc assemblages along the tropical-to-temperate transition in Japan (25° to 35° Northern latitude). Specifically, we use a trait database of 88 mollusc species from 31 subtropical reefs along the Pacific coast of Japan to show that trait composition of mollusc assemblages changes continuously along the latitudinal gradient. We discover that functional diversity of mollusc assemblages decreases with increasing latitude, a pattern associated with declines in functional dispersion. Moreover, we find a clear distinction between tropical and subtropical mollusc assemblages, with substrate-attached, suspension feeding bivalves more abundant in the tropics and free-living gastropod grazers more prevalent at higher latitudes. Our trait-based evidence in this study shows a contraction and almost complete shift in the functioning of marine mollusc assemblages at biogeographic transition zones and our trait database facilitates further study. Our findings provide evidence of the changing taxonomic and functional composition of extant mollusc communities with latitude, pointing to potential pertinent changes and tropicalisation of these communities with rapid ocean warming.

中文翻译：

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沿热带到温带梯度的珊瑚礁软体动物的功能多样性

全球变暖正在导致海洋物种的范围变化，威胁着依赖它们的生态群落和人口的结构和功能。最大的变化出现在生物地理过渡区，例如亚热带珊瑚礁群落，物种范围的变化已经导致大量的群落重组。这会导致亚热带纬度上群落的功能发生变化，尽管对许多分类群的基线功能理解仍然难以捉摸。一种重要的海洋分类群是软体动物，它提供许多生态系统服务，是鱼类的重要猎物，也是渔业目标，但在很大程度上仍未得到研究。在这里，我们检查性状组成、功能多样性、以及沿日本热带到温带过渡（北纬 25° 至 35°）的软体动物组合的功能冗余。具体来说，我们使用来自日本太平洋沿岸 31 个亚热带珊瑚礁的 88 种软体动物物种的性状数据库来显示软体动物组合的性状组成沿纬度梯度不断变化。我们发现软体动物组合的功能多样性随着纬度的增加而降低，这种模式与功能分散的下降有关。此外，我们发现热带和亚热带软体动物组合之间存在明显区别，热带地区更丰富的附着基质、悬浮进食的双壳类动物和自由生活的腹足类食草动物在高纬度地区更为普遍。我们在本研究中基于特征的证据表明，生物地理过渡区海洋软体动物组合的功能出现收缩和几乎完全转变，我们的特征数据库有助于进一步研究。我们的研究结果提供了现存软体动物群落的分类和功能组成随纬度变化的证据，指出这些群落随着海洋快速变暖而潜在的相关变化和热带化。