Seasonal Changes in the Sexual Size Dimorphisms of the Chelipeds and Pleons of the Porcellanid Crab Petrolisthes japonicus.

Decapod crustaceans develop secondary sexual structures, such as large chelipeds for weaponry and/or display in males and a wider pleon for incubating eggs in females. These structures should be costly to produce and maintain; hence, the crustacean reproductive strategy might have adapted to conserve energy for developing secondary sexual characteristics during the reproductive season. However, little is known about seasonal changes in the sexual size dimorphisms of the chelipeds and pleons of decapod crustaceans. Anomuran crabs from the family Porcellanidae exhibit a true crab-like body shape, with relatively large chelipeds for their body size and a well-developed pleon. They also show sexual size dimorphism (i.e., males with larger chelipeds and females with wider pleons); therefore, it was expected that seasonal changes in the sexual size dimorphisms of these organs would occur in porcellanid crabs. We tested this expectation using Petrolisthes japonicus, which is common on the intertidal cobble and boulder shores of the temperate and tropical regions of Japan. We employed allometric growth analyses of the cheliped and pleon dimensions of P. japonicus females and males collected over a year. Our analyses supported our expectation regarding the seasonal changes in the sexual size dimorphisms of the chelipeds and pleons in P. japonicus. Intersexual size dimorphism of the chelipeds and pleons was evident during the breeding season: females allocated more energy to pleon growth, while reducing cheliped growth, and investment in the pleon increased with increasing female body size, whereas males invested their energy in cheliped growth, and the investment in chelipeds increased with increasing male body size. During the nonbreeding season, females and males conserved energy by reducing the size of pleons and chelipeds relative to their respective body sizes. Our results highlighted the sex-specific and season-dependent resource allocation and reproductive strategies of porcellanid crabs.

Antifungal Prospect of Bacillus cereus Postbiotic on Crustacean Pathogen, Lagenidium thermophilum.

Pathogenic marine fungi, Lagenidium thermophilum is known causative agent in the crustacean industry. Current disinfection practice in hatchery has risks and negative impacts which prompts suitable substitute to synthetic antifungal agents. Thus, this study was conducted to evaluate the antifungal potential of postbiotic from four potential probiotics towards marine oomycetes, L. thermophilum IPMB 1401. The screening test showed that the Lactobacillus plantarum GS12 and Bacillus cereus GS15 postbiotics were positive for antifungal activity on L. thermophilum IPMB 1401. These two bacterial extracts have minimum inhibitory concentration （MIC） at 50%. The toxicity assay on MIC level of the postbiotic revealed that the cumulative mortality of brine shrimp nauplii exposed to B. cereus postbiotic was significantly lower compared to L. plantarum GS12 postbiotic and formalin. This indicates a high potential of B. cereus GS15 as a prospect for alternative control method for fungal infections in the crustacean culture industry.

Larval Performance of Amphidromous and Landlocked Atyid Shrimp Species in the Genus Paratya Under Different Temperature and Salinity Conditions.

Freshwater shrimps in the family Atyidae exhibit one of two life history traits: amphidromy, in which planktonic larvae develop in the sea; and landlocked, in which lecithotrophic larvae develop in freshwater. Temperature and salinity are the most important environmental factors that affect the survival, duration, and growth of decapod crustacean larvae. Larvae of landlocked shrimps are known to retain the ancestral habit of amphidromy, i.e., the ability to develop to the juvenile stage in saline water. Faster development exhibited by large larvae of landlocked shrimps is considered an adaptation that allows the larvae to stay in or near parental habitats. Therefore, information on larval performance under different temperature and salinity conditions is essential to obtain a better understanding of population connectivity through marine larval dispersal in amphidromous shrimps as well as larval adaptation to freshwater environments in landlocked shrimps. We examined the effects of temperature and salinity on the larval performance of two closely related atyid shrimps in the genus Paratya: the amphidromous P. compressa and the landlocked P. improvisa. Larvae were reared under the 25 combinations of five different temperatures (20, 23, 26, 29, and 32°C) and salinity levels (4.25, 8.5, 17, 25.5, and 34 ppt). In P. compressa, the rate of larvae that survived into the juvenile stage decreased linearly with increasing temperature and the larvae adapted to a wider range of salinity (8.5-34 ppt), though larval mortality increased at the high salinity (34 ppt) under the higher temperature conditions. In P. improvisa, larval survival rates were higher under a wider range of temperatures (20-29°C) in brackish water (4.25-17 ppt). Thus, P. compressa larvae may disperse broadly under the high salinity conditions of the open sea, but oceanic currents with high temperature and high salinity conditions may act as a barrier to restrict larval dispersion northwards from the southern islands. Paratya improvisa larvae adapted to a wider range of temperatures in natural freshwater environments and larval duration was shorter in P. improvisa than in P. compressa under the wide range of temperature and salinity conditions. Our results also highlight the retention strategy by which landlocked P. improvisa larvae stay in or near parental habitats.

Sexual Dimorphism and Reproductive Status of the Red Swamp Crayfish Procambarus clarkii.

The red swamp crayfish Procambarus clarkii is native to northeastern Mexico and the south-central USA, and it has expanded its distribution worldwide and negatively impacted the ecosystems in the invaded regions. The dynamics of the P. clarkii populations have been studied as the basis for the development of effective control measures against this invasive alien species. Adult males of P. clarkii exhibit a cyclical dimorphism between two sexual morphotypes; reproductive form I has large chelae and non-reproductive form II has small chelae. However, whether P. clarkii females have two sexual morphotypes and exhibit form alternation has not been resolved, and little is known about the degree of intra-sexual dimorphism of the chelae, even among males. We employed allometric growth analysis on the chelae dimensions of P. clarkii females and males that were collected from a small pond in Yokohama, Japan. Our analysis demonstrated the existence of form I, which has larger chelae, and form II, which has smaller chelae, in P. clarkii females and highlighted the intra- and inter-sexual dimorphisms in the chelae of this species. The reproductive cycle of the population was successfully traced by the reproductive status of P. clarkii based on the occurrence patterns of each sexual morphotype; the form I crayfish occurred throughout the sampling period from April to December, while the occurrences of form I females and males were highly correlated, peaking in October. Our results suggested that alternation of sexual forms occurs in P. clarkii females. The ability to discriminate between the sexual morphotypes based on chelae allometric growth would allow us to evaluate the female reproductive status more easily and precisely in invasive P. clarkii populations.

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.

Larval Performance of Amphidromous and Landlocked Atyid Shrimp Species in the Genus Paratya under Different Feeding Conditions.

Freshwater shrimps in the family Atyidae exhibit two life history traits: 1) amphidromy, with many small embryos hatching into planktotrophic larvae that develop in the sea, and 2) landlocked, with few large embryos hatching into non-feeding lecithotrophic larvae, or facultative lecithotrophic larvae that develop in freshwater. The lecithotrophy of larvae is considered an adaptation to limited food conditions in the freshwater environment. Furthermore, faster development and settlement behaviours that large larvae exhibit are considered adaptations that allow the larvae to stay in or near parental habitats in fast-flowing streams. We therefore hypothesized that the facultative lecithotrophic larvae of landlocked shrimps might better adapt to limited food conditions as their large body size develops, an adaptation to maintain habitat position in flowing streams, than do planktotrophic larvae of companion amphidromous species developing in the sea. To test this hypothesis, we compared the larval feeding habits and size of two closely related species in the genus Paratya: the amphidromous P. compressa, with planktotrophic larvae, and the landlocked P. improvisa, with facultative lecithotrophic larvae. Larvae were reared by being fed commercially preserved or cultured phytoplankton (Tetraselmis sp.) and cultured zooplankton rotifers. Paratya compressa larvae did not survive, but P. improvisa larvae did develop into the juvenile stage under poor feeding conditions with preserved Tetraselmis alone, supporting our hypothesis of the effects of different larval feeding habits in amphidromous and landlocked atyid shrimp species. Hatchlings were larger and larval duration was shorter in P. improvisa than in P. compressa. Paratya improvisa larvae exhibited settlement behaviour beginning with the early zoeal stage. Our results also highlighted the retention strategy by which landlocked P. improvisa larvae stay in or near parental habitats.

Rigorous monitoring of a large-scale marine stock enhancement program demonstrates the need for comprehensive management of fisheries and nursery habitat.

Release of captively-bred individuals into the wild is one of the most popular tools in fisheries, forestry, and wildlife management, and introgression of hatchery-reared animals into wild populations is of global concern. However, research and monitoring of impacts on wild populations are generally lacking, and the benefit of hatcheries for long-term fisheries and conservation goals is unclear. Using spatio-temporal genetic monitoring and a four-dacade time series of catch data, we quantified the effects on the size and genetic diversity of wild populations of one of the world's largest marine stock enhancement programs-the red sea bream (Pagrus major) in Kagoshima Bay, Japan. Our analyses found that the stock enhancement program reduced genetic diversity of the population, but the genetic effect diminished with increased size of the wild population. Increases to the seaweed communities and reduced fishing efforts were the primary factors associated with the wild population recovery; effects of aquaculture were much smaller. Our results represent crucial evidence that hatcheries for enhancement and conservation of populations cannot be successful over the long term unless sufficient efforts are also made to reduce harvest rates and rehabilitate natural habitats.

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.

Larval development of the land hermit crab Coenobita violascens Heller, 1862 (Decapoda, Anomura, Coenobitidae) described from laboratory-reared materia.

The zoeal and the megalopal stages of the land hermit crab Coenobita violascens Heller, 1862 are described and illustrated from laboratory-reared material, and compared with larvae of nine other described coenobitid species. The larvae developed through four planktonic zoeal stages to the megalopal stage. Coenobita violascens had characteristics of zoeal pleomeres and megalopal antennules typical of those found in other Coenobita species, excluding C. brevimanus.