Supporting data for Ecology of Semi-terrestrial Crabs Found in Back Mangroves and Adjacent Woodlands in the Monsoonal Tropics

The colonization of land from the sea, known as ‘terrestrialization’, occurred relatively recently among Brachyuran crabs (Decapoda, Crustacea). Many crab species invaded the supralittoral and terrestrial environment from the sea via intertidal habitats, which involves crabs spending most of their time in air and facing the challenges of temporal variations in temperature, water salinity and availability, and changes in food sources. This thesis studies the various adaptations to semi-terrestrial life in eight species of semi-terrestrial crabs common in the back mangroves and adjacent riparian woodland in Hong Kong (Chiromantes haematocheir , Orisarma patshuni, Orisarma intermedium, Orisarma dehaani, Neosarmatium indicum, Parasesarma continentale, Parasesarma pictum and Chasmagnathus convexus) to identify their behaviours, life histories and gut microbiomes, as well as the potential resource partitioning that allows their co-existence.The distribution of the semi-terrestrial crabs was defined by the salinity gradient, with only two species (C. haematocheir and O. patshuni) expanding into the riparian woodlands, while the remaining species were confined to the back mangroves and other lower shore habitats. Within the riparian woodlands, C. haematocheir was more abundant than O. patshuni at higher elevations, suggesting it was better adapted to the low salinity and variable water conditions in upper stream areas. These two riparian woodland species had slower growth rates and longer lifespans compared with species that live in intertidal habitats.To cope with variable environmental conditions, crabs showed seasonal activity patterns, with higher activity in the wet-and-hot summer than in the cold-and-dry winter. Temperature was a key factor, as the abundances of C. haematocheir and O. patshuni were positively correlated to mean daily temperatures. Burrows were refuges for N. indicum and C. convexus, which they remained in throughout winter and when the soil surface was hotter than the temperature in the burrows in summer.In terms of diet, the crabs showed subtle partitioning of food sources. Apart from P. pictum, which consumed more animal tissues, the other species ingested large amounts of plant materials. Differences in the freshness of consumed leaves were found: whilst most crabs consumed leaf litter, O. intermedium consumed more green leaves . The crabs also relied on soil microalgae and animal tissues to supplement their diets. Competition for food might induce caching behaviour in summer as N. indicum and C. convexus brought potential food sources into burrows more frequently in areas with higher burrow density. This caching of leaf litter improved leaf palatability as it promoted the leaching of phenolic compounds, especially in winter. The gut microbiomes of the crabs reflected their phylogeny, habitat and food sources and may improve their nutrition by providing essential amino acids and vitamins.In summary, this thesis highlights the variety of potential adaptations of semi-terrestrial crabs to survive in the challenging supralittoral habitats, which may be used to inform their conservation, given the threats to their habitats now and in the future.

陆地从海洋的殖民化过程，亦即所谓的‘陆化’，在短尾类螃蟹（甲壳动物门，十足目）中相对较晚发生。众多螃蟹物种通过潮间带生境从海洋侵入潮间带和陆地环境，这要求螃蟹大部分时间生活在空气中，并面对温度、水盐度及其可获取性以及食物来源变化的时序挑战。本论文研究了香港后红树林及相邻河岸林地中常见的八种半陆生螃蟹（Chiromantes haematocheir, Orisarma patshuni, Orisarma intermedium, Orisarma dehaani, Neosarmatium indicum, Parasesarma continentale, Parasesarma pictum 和 Chasmagnathus convexus）对半陆生生活的各种适应性，以识别其行为、生命周期和肠道微生物组，以及允许其共存的可能资源分配。半陆生螃蟹的分布由盐度梯度界定，其中仅有两种物种（C. haematocheir 和 O. patshuni）扩展至河岸林地，而其他物种则局限于后红树林及其他低海岸生境。在河岸林地内，C. haematocheir 在较高海拔处比 O. patshuni 更为丰富，暗示其更能适应上游地区低盐度和多变的水质条件。这两种河岸林地物种的生长速度较潮间带栖息地物种缓慢，寿命更长。为了应对多变的环境条件，螃蟹展现出季节性的活动模式，在潮湿炎热的夏季活动频率高于寒冷干燥的冬季。温度是关键因素，因为 C. haematocheir 和 O. patshuni 的丰富度与平均日温度呈正相关。洞穴是 N. indicum 和 C. convexus 的避难所，它们在整个冬季以及夏季土壤表面温度高于洞穴内温度时都留在洞穴内。在饮食方面，螃蟹对食物来源进行了细微的划分。除了 P. pictum 摄食更多动物组织外，其他物种摄入大量植物材料。研究发现摄食叶子的新鲜度存在差异：尽管大多数螃蟹摄食落叶，但 O. intermedium 摄食更多绿叶。螃蟹还依赖土壤微藻和动物组织来补充其饮食。在夏季，食物竞争可能诱导储存行为，因为 N. indicum 和 C. convexus 在洞穴密度较高的区域更频繁地将潜在食物来源带入洞穴。这种储存落叶的行为提高了叶片的可食性，因为它促进了酚类化合物的淋溶，尤其在冬季。螃蟹的肠道微生物组反映了其系统发育、栖息地和食物来源，并通过提供必需氨基酸和维生素来改善其营养。总之，本论文突显了半陆生螃蟹适应挑战性潮间带生境的多样性潜在适应性，鉴于其生境目前及未来的威胁，这些适应性或许可用于指导其保护工作。