Seasonal changes in body color of Mictyris guinotae (Brachyura: Mictyridae)

Abstract

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.