This study aims at investigating of dynamic states of larvae of land hermit crab Coenobita brevimanus in Amitori Bay, Iriomote Island, Japan from the perspective of numerical analysis. An ecological investigation of Coenobita brevimanus was conducted to provide input data for a numerical model. Reproduction of coastal currents in Amitori Bay was done using a coastal ocean current model CCM. The dynamic states of larvae of Coenobita brevimanus were examined using particle tracking analysis based on the ecological investigation and the current field reproduced by the CCM. Coenobita brevimanus is speculated to employ a strategy to maintain the group of individuals by making most of the larvae stay around the release place.

The body color of the soldier crab, Mictyris guinotae, varies from a pale blue to a dark ink-blue. We describe the composition of black and blue body color forms in animals obtained during a year-long collection effort. Body color showed clear seasonal changes; almost all crabs were black between April and September (non-breeding season) and blue between late November and February (breeding season). Larger black crabs, 7 mm in carapace length, first showed blue coloration in October, suggesting that color change is associated with sexual maturity. Some newly molted black individuals with white exuviae were found inside the burrow in March. The timing of the color change from blue to black was later in females because ovigerous females are unable to molt. Black body color during summer months may mitigate the harmful effects of ultraviolet radiation and provide visual crypsis from predators during activity on the surface of sand flats.

No abstract