Land Crabs

Two species of land crabs (Chiromantes haematocheir and C. dehaani) inhabit coastal forests in Noto Peninsula, Ishikawa Prefecture, Japan. The adult crabs inhabit coastal deciduous and evergreen forests. They feed mainly on fallen leaves, but also harvest fresh leaves, mushrooms, nuts and invertebrates in the forests. To remove toxic substances from the leaves and aid digestion, Chiromantes crabs either buried the leaves in the soil or soaked them in the water. Each adult female releases up to tens of thousands eggs into the sea from July to September each year. The numbers of the females that released eggs increased steadily from the new moon to the full moon, with fewer numbers observed when avian predators and/or humans were present. Both eggs and larval stages of Chiromantes are important food sources for a variety of small marine fish, such as the striped mullet (Mugil cephalus). M. cephalus, in turn, are fed by larger fish species including the Japanese sea perch (Lateolabrax japonicus). The larval stage (zoea) of Chiromantes species was both abundant and widely distributed around Noto Peninsula and, therefore, they play a crucial role in supporting rich marine faunal diversity in the region. The crabs return to the terrestrial habitats as they reach the juvenile stage between late September and October. Degradation of coastal habitats poses a major threat to Chiromantes. For example, the juvenile Chiromantes were abundant in the reed (Phragmites spp.) grasslands, with the average density of 100 individuals m-2. Their densities, however, declined significantly to approximately 40, five and zero individuals m-2 in the concrete grounds with fallen leaves, the sandy soils and the concrete grounds without fallen leaves, respectively. Our presence/absence survey of Chiromantes in the terrestrial environments and the comparison with the historical data indicated that they have disappeared at least from twelve monitoring locations within Noto Peninsula. These locations, where haematocheir and C. dehaani have disappeared, typically suffered from coastal forest and grassland removal, housing constructions and/or concrete embankments. Concrete embankments, in particular, prevented the movements of Chiromantes. Therefore, it is important to create corridors so that Chiromantes could continuously utilise both marine and terrestrial habitats. Thus, we conclude that ensuring the connectivity between satoyama and satoumi is crucial for supporting sustainable ecosystems in Noto Peninsula.

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