Characterization of Aquimarina hainanensis isolated from diseased mud crab Scylla serrata larvae in a hatchery.

Mass mortality due to necrosis signs occurred in hatchery-reared zoea stage larvae of the mud crab Scylla serrata in Okinawa, Japan, and a causative bacterium was isolated. In this study, we identified and characterized the bacterium by genome analysis, biochemical properties and pathogenicity. The bacterium was a Gram-negative, non-motile, long rod, forming yellow colonies on a marine agar plate. It grew at 20-33°C (not at 37°C) and degraded chitin and gelatin. Phylogenetic analysis of the 16S rRNA gene sequence identified the bacterium as Aquimarina hainanensis. Genome sequence data obtained from Illumina MiSeq generated 29 contigs with 3.56 Mbp in total length and a G + C content of 32.5%. The predicted 16 chitinase genes, as putative virulence factors, had certain homologies with those of genus Aquimarina. Experimental infection with the bacterium conducted on larvae of four crustacean species, brine shrimp Artemia franciscana, freshwater shrimp Caridina multidentata, swimming crab Portunus trituberculatus and mud crab S. serrata, revealed that this bacterium was highly virulent to these species. The present study suggests that the bacterium caused mass mortality in mud crab seed production was A. hainanensis and can be widely pathogenic to crustaceans.

Expansion of the Northern Geographical Distribution of Land Hermit Crab Populations: Colonization and Overwintering Success of Coenobita purpureus on the Coast of the Boso Peninsula, Japan.

The present study aimed to elucidate the population dynamics of land hermit crabs on the coast of the Boso Peninsula, Chiba Prefecture, Japan, which is the northern limit of their geographical distribution. We conducted monthly field surveys at four sites from April 2012 to December 2014 and visually searched for crabs. Laboratory experiments were also conducted to evaluate the overwintering ability of two species, Coenobita purpureus and C. rugosus, which were detected during the field surveys; adult crabs and laboratory-raised juveniles were exposed to low-temperature conditions that simulated the in situ temperatures during the early overwintering period. Newly landed juveniles first appeared in August. They were identified as either C. purpureus or C. rugosus, with C. purpureus being the dominant species. Early juveniles grew until October. The abundance of early juveniles decreased with decreasing air temperatures, and dead individuals were found during the overwintering period. The low-temperature tolerance ability of C. purpureus was stronger than that of C. rugosus. Some crabs successfully overwintered, and all were identified as C. purpureus. The growth and overwintering success of juveniles varied among the survey sites depending on the local temperature regime. Our results highlight the frontier for expanding the northern geographical distribution of land hermit crab populations by the colonization and overwintering success of C. purpureus.

Ontogenetic change of body color patterns in laboratory-raised juveniles of six terrestrial hermit crab species.

We examined the ontogenetic change of body color patterns in the laboratory-raised juveniles of six terrestrial hermit crab species, including Birgus latro, Coenobita brevimanus, C. cavipes, C. purpureus, C. rugosus, and C. violascens, which commonly occur in the southern islands, Japan. The body color patterns of coenobitid juveniles were species-specific. The diagnostic features of body color patterns enable identification of juveniles of coenobitid crab species in the wild, thereby helping to understand the precise habitats of each coenobitid species.