Brackish-water crab <i>Deiratonotus cristatus</i> in Tokyo Bay, Japan, with different life history traits from nearby populations

The camptandriid crab Deiratonotus cristatus inhabits brackish, muddy-bottomed tidal channels and streams, but has experienced a drastic decline due to habitat deterioration, leading to its designation as an endangered species in Japan. Although historically abundant in Tokyo Bay, sightings of the species had ceased for several decades until 2008 when the species was rediscovered. Since D. cristatus had been undetected in Tokyo Bay for decades, we considered the possibility that the population in Tokyo Bay might have been introduced from other regions or overseas. Therefore, as an initial step in our research, we conducted a 13-month study from October 2011 to November 2012 to elucidate the life history traits of the study population. This revealed D. cristatus longevity of approximately 2 years, with recruitment in late summer and ovigerous females holding eggs in the second overwintering period. The D. cristatus population in Tokyo Bay, where females appear in the cool season, differed from several nearby Pacific Coast populations that exhibit this trait in the warm season. The presence of eggs during the cool season is considered consistent with the traits of genotypes from Kyushu and the Seto Inland Sea, which differ from the Pacific type, where ovigerous females appear during the warm season. Thus, although the possibility of introduction via ballast water or fisheries trade cannot be ruled out, the distinct life history of the Tokyo Bay population could represent the uniqueness of the breeding season in the Pacific coast populations.