Abstract

The distribution, morphology, population density, and adult sex ratio of fiddler crabs in southern Thailand were studied. Nine (sub-)species of fiddler crab were found: Uca lactea annulipes (H. Milne Edwards, 1837), U. triangularis bengali Crane, 1975, U. forcipata (Adams & White, 1848), U. vocans hesperiae Crane, 1975, U. lactea perplexa (H. Milne Edwards, 1837), U. rosea (Tweedie, 1937), U. paradussumieri Bott, 1973, U. tetragonon (Herbst, 1790), and U. urvillei (H. Milne Edwards, 1852). Three forms occurred in both the Andaman Sea and the Gulf of Thailand: U. v. hesperiae, U. forcipata, and U. l. annulipes. The population densities of these three were higher in the Andaman Sea. In four species, more than 50% of the males were right-handed: U. tetragonon, U. t. bengali, U. v. hesperiae, and U. forcipata. More than 50% of the males in eight out of the nine species had brachychelous claws. Only U. tetragonon males had brachychelous and leptochelous claws in equal proportions. Six out of nine species in the Andaman Sea and two out of three species in the Gulf of Thailand had male-biased sex ratios.