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In the Sea of Japan, the mature red snow crab Chionoecetes japonicus is distributed at a depth of 500���2,700 m. However, its planktonic larvae occur at depths shallower than 300 m. To better understand the factors influencing larval dispersal and settlement of the red snow crab in its natural habitat, we tested the effects of temperatures ranging from 1��C to 18��C on the survival, developmental period, and growth of red snow crab zoeal and megalopal larvae. The mean number of days from hatching to second zoeae and megalopae and from megalopae to the first crab instar was significantly shorter at warmer temperatures. Moreover, the relationships between mean temperatures and larval periods were well described by heat summation theory equations and a nonlinear thermodynamic Sharpe-Schoolfield-Ikemoto (SSI) model. The higher survival rate, intrinsic optimum temperatures in the SSI model, and larger carapace width suggested that the optimum temperatures for the development of zoeal and megalopal stages of the red snow crab are 9���10��C and 7���8��C, respectively. A lower optimum temperature in the megalopal stage than in the zoeal stages was considered an adaptation to facilitate deeper vertical distributions in the megalopal stage.

Post-autotomy appendage movement has evolved independently in several vertebrate and invertebrate taxa. Moving appendage may divert a predator’s attention away from the body, allowing the prey to e...

We examined the effects of temperature and salinity on larval survival, duration, and growth of three amphidromous atyid shrimps, Caridina leucosticta, C. multidentata, and C. typus to infer larval dispersal strategy in the sea. Larvae were reared under 25 combinations of five different temperature (20, 23, 26, 29, and 32°C) and salinity (4.25, 8.5, 17, 25.5, and 34 ppt) levels. Interspecific variability was detected in larval performance: C. leucosticta larvae were able to survive to moult into the juvenile stage at the lower salinity condition (8.5 ppt), C. multidentata larvae exhibited an ability to adapt to the wide range of salinity condition (17–34 ppt), and C. typus larvae adapted to the higher salinity condition (34 ppt) better than C. leucosticta larvae. Larval duration was less variable between species. Thus, salinity adaptation of larvae may play an important role in mediating the larval dispersal of the three Caridina species in the sea. Larval dispersal range may be most limited near the river mouth for C. leucosticta, and be moderate for C. typus, and C. multidentata larvae may be able to disperse broadly under the high salinity condition of the open sea.

The East Asian common octopus Octopus sinensis is a bottom-dwelling species, but goes through a planktonic phase as ‘paralarvae’ during the first several weeks of life. As the swimming performance of the paralarvae is relatively poor, their dispersion relies primarily on ocean currents; however, vertical swimming may play an important role in their horizontal dispersion by controlling their buoyancy in the current. Within this context, ontogenic changes in vertical swimming in relation to the ambient water flow are key to understanding the dispersion properties of the paralarvae and the subsequent onset of settlement, yet this information remains largely unknown. Here, we investigated the effects of different water flows (downward × 4 velocities, stagnant and upward × 5 velocities) on the vertical swimming position in test columns using laboratory-raised O. sinensis paralarvae aged 0, 5, 10 and 15 days during the day and at night. Paralarvae younger than 10 days ( 5 mg) commenced short clinging behaviour, and their swimming positions dispersed downwards during daytime regardless of the water flow, indicating the onset of the transition to settlement. In contrast, their position shifted to near the upper limit at night by swimming upwards, even under downward water flows. Our results suggest that O. sinensis exhibits characteristic behaviour that alternates between diurnal descent dispersion with clinging (hyperbenthic trait) and nocturnal upward swimming (planktonic trait) during the transition to permanent benthic life.

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.

Because temperature strongly influences biological processes of ectotherms, they must adapt to the thermal conditions of their habitats. We evaluated the upper thermal tolerance of early juveniles of six terrestrial hermit crab species in the family Coenobitidae (genera Birgus and Coenobita), B. latro, C. brevimanus, C. cavipes, C. purpureus, C. rugosus, and C. violascens, that occur in the northwestern Pacific region of Japan. A total of 30 laboratory-raised juveniles (approximately 1 mm in shield length) carrying gastropod shells were individually stocked in small plastic cups with sandy bottoms in temperature-controlled incubation chambers at ∼27°C. The temperature was increased by 1°C every 48 h, and the juveniles were observed until all the crabs had died. The median upper lethal temperature was estimated as the temperature at which 50% of the test juveniles had died. The median upper lethal temperature estimates significantly varied among the species. Coenobita violascens, which mainly occurs in mangrove estuaries with lower thermal conditions, had the lowest median upper lethal temperature values. The median upper lethal temperature values estimated for B. latro were slightly lower than those for the other Coenobita species, probably reflecting its cryptic nature in natural habitats during the juvenile stage. The most northerly distributed species, C. purpureus, had the highest median upper lethal temperature values, suggesting the existence of common physiological mechanisms that regulate both upper and lower thermal tolerance abilities.

Gastropod shells are vital resources for hermit crabs for their growth, reproduction and survival. However, the land hermit crab Coenobita spinosus, which lives in wet and dark coastal forests, she...

Metamorphosis season of megalopae to the first crab stage in snow crab Chionoecetes opilio and red snow crab C. japonicus was inferred by culturing wild-born megalopae collected from the Se...

Despite recent advances in culture technology for East Asian common octopus Octopus sinensis paralarvae using upwelling systems, securing suitable feed for the paralarvae is an unresolved issue. The zoea of the swimming crab Portunus trituberculatus is a good candidate for paralarval feed because of the high fecundity of the adult females. To investigate the effects of supplying P. trituberculatus zoeae and their feeding method on paralarvae, we cultured paralarvae with supplying different combination ratios of zoeae and Artemia (10:0, 7:3, 5:5, 3:7 and 0:10), and with or without supplementing rotifers using small‐scale (3‐L) upwelling systems. Paralarval survival rate and growth were improved when zoeae were supplied as the main feed, but reduced when the proportion of Artemia exceeded half the whole preys. Supplementing rotifers did not affect the paralarval survival and growth. Subsequently, paralarvae were cultured by supplying zoeae (partially augmented by Artemia) using three large (1‐kl) upwelling systems to assess their feeding effectiveness in juvenile octopus production. Paralarvae could be cultured at high survival rates of 77.1 ± 5.1% to reach benthic juveniles at 23 days after hatching. In conclusion, supplying P. trituberculatus zoeae augmented with Artemia under an upwelling culture system has great potential for juvenile octopus production.

Because temperature strongly influences biological processes of ectotherms, it also plays a fundamental role in determining their geographical distribution. We evaluated the low-temperature tolerance of early juveniles of six terrestrial hermit crab species in the family Coenobitidae (genera Birgus and Coenobita), B. latro, C. brevimanus, C. cavipes, C. purpureus, C. rugosus, and C. violascens that occur in the northwestern Pacific region, Japan. A total of 30 laboratory-raised juveniles (about 1 mm in shield length) carrying gastropod shells were individually stocked in small plastic cups with sandy bottoms in temperature-controlled incubatory chambers at ∼27°C. The temperature was reduced by 1°C every 48 h, and the juveniles were observed until all the crabs had died; the median lethal temperature (MLT) was estimated as the temperature at which 50% of the test juveniles had died. The MLT estimates varied significantly among the species, and the most northward distributed species, C. purpureus, had the lowest MLT values. The phylogeny, paleoceanography, paleogeography, and paleoclimatology suggest that cooler thermal regimes might have acted as an evolutionary force for the divergence of C. purpureus in the Pliocene. A negative correlation was found between the northern latitudinal limit of distribution and the MLT values, even after controlling for the phylogenetic relationships in the six coenobitids. A temperature-dependent biogeography was thus recognized in terrestrial hermit crab species in the northwestern Pacific region, and global warming is expected to affect their geographical distributions.

Fungal infections have been reported as one of the main hindrances for successful crustacean seed production. In a shrimp hatchery of Universiti Malaysia Sabah, abnormal sponge development of the ornate spiny lobster Panulirus ornatus was observed and it was suspected as fungal infection due to a change in sponge colour. Fungus was isolated from egg samples of P. ornatus and transferred to Peptone-Yeast-Glucose-Seawater (PYGS) agar to identify and to reveal its morphological characteristics. Interestingly, the isolate in PYGS broth transferred into sterilized seawater did not show any characteristic feature of any asexual reproduction of Oomycete infection on crustacean. Consequently, slide culture was performed for a more detailed examination, where the fungus isolate showed septate hyphae and vesicle-like fruiting body only upon staining via Iodine-Glycerol stain. Based on the morphological characteristic features, the present isolate was determined as a non-oomycete organism and designated as IPMB LE01 strain. According to the ITS nucleotide sequence analyses of IPMB LE01, it has matched to Zasmidium musae. This species was mainly reported in plant fungal infection and rarely observed in aquatic animals. Hence, it is considered as the first report of fungus-associated on the moribund eggs of ornate spiny lobster in Sabah.

Artemia are potential food organisms for the mass culture of common octopus paralarvae but cause poor paralarval growth and mortality. To understand problems arising from Artemia use, we focused on Artemia flocculation in paralarval culture tanks; Artemia get caught up with each other, exhibit disrupted swimming, are deposited on the tank bottom and eventually die. To clarify whether paralarvae induce the flocculation of food organisms or not, we cultured newly hatched Artemia nauplii, 3-day-old metanauplii and decapod crustacean zoeae with or without paralarvae at different growth stages (weight). Flocculation occurred only when Artemia were cultured with paralarvae; metanauplii had a higher susceptibility for flocculation than nauplii. Flocculated Artemia proportion increased with increasing paralarval weight. Scanning electron microscopy revealed that flocculated metanauplii had deformed setules on their setae, with hook-shaped tips and adhesion of neighbouring tips, suggesting that flocculation may occur via a mechanism similar to the ‘hook-and-loop fastener’. As octopus paralarvae exhibit external digestion, digestive enzymes secreted by paralarvae may deform Artemia setules and result in flocculation. As flocculation did not occur when metanauplii were cultured in water in which paralarvae were cultured and then removed, causative enzymes were probably rapidly inactivated after secretion.

The present study was conducted to examine the occurrence and distribution of early juvenile land hermit crabs of the genus Coenobita on a small beach on the Boso Peninsula, Japan as a basis for understanding the important habitats that land hermit crabs use during the sea-to-land transition. The survey sites were supratidal zones at six points with heterogeneous topography, and visual surveys for early juveniles were conducted from middle July to late October in 2015 and 2016. The number of empty gastropod shells in four quadrats along the intertidal zone at each point was also counted in the 2016 survey. The occurrence of early juveniles varied among survey points and was spatially stable for two successive years. The first appearance and abundance of early juveniles varied among survey years. Early juveniles were abundant at points with a gravel bottom throughout the intertidal zone, and empty gastropod shells were also abundant at these points. The abundance of early juveniles was highly correlated with the amount of empty gastropod shells. Thus, our surveys suggested the importance of the sediment types and abundance of empty gastropod shells in the intertidal zones for settlement and landing by land hermit crabs.

Despite a growing interest in common octopus for aquaculture, massive mortalities during the planktonic paralarval stage still hamper production. Prior to die-off during rearing trials for paralarvae, it could be observed that the food-capturing paralarvae tended to be carried downward in a current induced by the aeration system, eventually depositing the animals on the tank bottom. The aim of this study was to investigate the effect of upwelling water-flow, that might support paralarval swimming and floating, on paralarval survival and growth. A new artificial upwelling rearing system using a strong downward flow in the center to the bottom of the tank was developed. The effects of the new system in combination with supplying natural zooplankton (mainly decapod crustacean zoeae) or Artemia were evaluated using three different broods hatched from three mothers (broods A, B, and C). As food items for zooplankton, n-3 highly unsaturated fatty acid (n-3 HUFA)-fortified rotifers and digestible microalgae Nannochloropsis oculata were supplemented. The hatchling dry weight was significantly different among broods, showing heavier weight in order of broods A > C > B. Use of the upwelling rearing system significantly improved the rate of paralarval survival as compared with using the standard system, and paralarval growth was significantly faster when reared in the upwelling system with zooplankton supplementation. Paralarvae in the upwelling + zooplankton group kept high survival rates over 80% until 18 days after hatching (DAH). The survival rate of the tank of brood A could achieve 80.8% at 20 DAH, however, those of broods B and C dropped to 8.2% and 54.4% at 20 DAH, respectively, presumably due to combined effect of small hatchling size and insufficient food supply. The octopuses of broods A and C reached benthic stage by 25 and 23 DAH, with survival rates of 51.0% and 45.3%, respectively. The overall results suggest that an inadequate water-flow environment in combination with poor food quality and quantity are major causes of paralarval mortality of the common octopus. For culturing paralarvae, the combined use of an upwelling rearing system and supplying decapod crustacean zoeae supplemented with n-3 HUFA fortified rotifers and digestible N. oculata was recommended.

Microalgae concentrates are important for hatchery operations but have been found to contain high concentrations of bacteria. Therefore, this study investigated the effects of four thermal disinfection and sterilisation treatments, low‐temperature long‐time (LTLT; 62–65°C, 30 min), high‐temperature short‐time (HTST; 72–75°C, 15 s), ultra‐high‐temperature (UHT; 120–150°C, 1–3 s) and high‐temperature high‐pressure (HTHP; 121°C, 0.2 MPa, 15 min), on concentrates of the microalgae, Chaetoceros gracilis, Chlorella vulgaris (fortified with eicosapentaenoic acid and docosahexaenoic acid) and Nannochloropsis oculata. The concentrates had reduced bacterial counts following LTLT, HTST and UHT and were completely sterilised by HTHP. Furthermore, cell dispersibility was retained in all treatment groups except HTHP‐treated C. gracilis. Rotifers that were cultured with HTHP‐treated C. vulgaris and N. oculata experienced significant population increases, whereas the survival rate and growth of Artemia nauplii significantly improved when supplied with HTHP‐treated N. oculata, indicating that HTHP enhances the digestibility of this microalga. HTHP did not affect the total lipid content and fatty acid composition of the microalgae. These results suggest that HTHP‐treated C. vulgaris and N. oculata could be used for the nutritional enrichment of rotifers and Artemia, while avoiding the risk of bacterial contamination, and would have an increased shelf life at room temperature.

Skeletal deformities are one of the serious problems in hatchery‐reared longtooth grouper (Epinephelus bruneus). In this study, seed production of longtooth grouper was carried out in four large hatchery‐grade tanks. Osteological development of the vertebral column, caudal‐fin skeleton and dorsal‐fin supports in larvae and juveniles was described. The vertebral ontogeny started at 4.8 mm total length (TL) with the formation of neural spines 2 and 3, and the vertebral centra began forming at 5.3 mm TL. By 16 mm TL, all vertebral bony elements were formed except for the dorsal ribs. The onsets of the ontogeny of the caudal‐fin skeleton and dorsal‐fin supports occurred at approximately 5.1 mm and 3.9 mm TL, respectively, and the completion of these bony elements occurred at approximately 20 mm TL. The incidence of deformity was examined; some type of deformity was observed in 57%–68% of the specimens. These deformities mainly occurred as three types: lordosis, around vertebrae 1–5; saddleback‐like syndrome, around vertebrae 7–11; and vertebrae fusion, around vertebrae 22–24. The incidence of prehaemal lordosis was significantly higher among individuals with an uninflated swim bladder than among those with an inflated swim bladder.

Larval sinking causes larval mass mortality during seed production in the horsehair crab, Erimacrus isenbeckii. Under normal light conditions, horsehair crab larvae generally show negative phototactic behaviour and sink in their rearing seawater. It has been proposed that culturing larvae in the dark may prevent larval sinking. Herein, we examined the effect of photoperiods on horsehair crab larval survival and development to facilitate the development of larval rearing techniques that prevent sinking. Newly hatched larvae were reared with Artemia to the first crab stage in 2‐L beakers under five photoperiods: 0L:24D, 6L:18D, 12L:12D, 18L:6D and 24L:0D. Larvae survived and molted to the first crab stage under all tested photoperiod conditions. The survival rate improved with increasing light period, whereas the developmental period for each larval stage decreased with increasing light period. Longer light periods increased the carapace length at the first crab stage. Our results suggest that larvae could be cultured to the first crab stage in large‐scale tanks under constant darkness. However, significantly improved larval performance under longer photoperiodic conditions indicates a need for developing alternative culture techniques to control larval behaviour in the seed production tank.

Settlement is the process whereby benthic octopuses with a planktonic paralarval phase make a behavioural change from being active swimmers to assume adult life on the seabed . This process is poorly understood, mainly because octopus juveniles are highly cryptic in the natural habitat and they lack any distinct morphological changes (i.e. metamorphosis) in concert with settlement. To investigate behaviour during the settlement process, ontogenetic changes in swimming, clinging and shelter-utilizing behaviours were examined during both day- and night-time using laboratory-raised East Asian common octopus, Octopus sinensis, aged from 10 to 28 days after hatching (ranging from 1.7 to 16.4 mg mean dry weight, DW). The accompanying change in feeding habit from planktivorous to benthivorous was assessed by comparing rates of consumption of planktonic zoea (of the swimming crab Portunus trituberculatus ) and benthic juveniles of the Manila clam , Ruditapes philippinarum . During the daytime, octopus behaviour changed rapidly from swimming to clinging onto the surface of the wall and bottom of the test tank during growth from 3 to 9 mg DW. At night, the frequency of clinging behaviour increased along with growth but the behavioural change progressed more slowly, indicating a tendency to continue swimming during darkness. Shelter utilization during the day commenced mainly after reaching 8 mg DW, after which shelter use gradually increased with growth. In contrast, shelter utilization at night was rarely observed throughout the experiment. Regarding octopus prey preference , consumption of clam juveniles increased with growth while zoeae consumption remained constant. The increase in clam consumption, however, was gradual, indicating that the shift of feeding habit from planktivorous to benthivorous is by no means an abrupt transition. These results indicate that O. sinensis requires a considerable period of time to complete the transition to benthic life. The alternating behaviours of diurnal clinging and nocturnal swimming in the water column may facilitate safe migration of the octopuses from the location to which they have been passively advected towards a more suitable benthic habitat while minimizing their exposure to visual predators. Since shelter utilization and feeding on bivalves are likely to require the use of a certain degree of force and complex coordination of the arms and suckers, the extended, gradual increase in shelter utilization frequency and clam consumption may be attributable to the degree of arm and sucker development.

Terrestrial hermit crabs in the family Coenobitidae (genera Coenobita and Birgus) are distributed in tropical and subtropical regions. They occupy various habitats ranging from shore to inland forests, and the two shore-dwelling species, Coenobita rugosus and C. violascens, possess different distributional characteristics on Ishigakijima Island, Ryukyu Archipelago, Japan. Coenobita rugosus is distributed throughout the coast of the island and is abundant in beach areas, whereas C. violascens has mainly been found in river mouth areas. However, very little is known about the habitats used by the early life stages of coenobitid crabs because identifying the species of recently landed early juveniles is difficult. We tested whether the species compositions of early juveniles of coenobitids differed between beach and river mouth sites on Ishigakijima Island. We collected and identified the early stage coenobitids using PCR–RFLP techniques. A total of 576 early juveniles of five Coenobita species were collected, of which 0.7% were C. brevimanus, 7.3% were C. cavipes, 0.2% were C. purpureus, 70.1% were C. rugosus, and 21.7% were C. violascens. The early juveniles of Birgus latro were not found. The early juveniles of C. rugosus occurred at both beach and river mouth sites, and they were abundant at beach sites. The early juveniles of C. violascens were only found at river mouth sites. These findings indicate that C. rugosus and C. violascens complete their life cycles on land near the localities where they land. The early juveniles of the inland-dwelling species, C. cavipes, were also mainly collected from river mouth sites, which suggested that juveniles of C. cavipes selected landing sites near river mouth areas and then migrated into the inland forests, passing through riverside areas. Our results highlighted the importance of river mouth areas for recruitment to adult habitats by some coenobitid species.

Seed production of the swimming crab Portunus trituberculatus in Japanese hatcheries frequently shows larval mass mortality because of abnormal morphologies and nutritional deficiencies. We conducted two laboratory experiments to explore the optimal food conditions for larval culture in this species. In experiment 1, hatchlings of three mothers were separately reared under different supplementation densities of digestible Nannochloropsis oculata for feeding to the Artemia nauplii provided to larvae. In experiment 2, hatchlings of three other mothers were separately reared under different supply densities of Artemia nauplii that had been cultured with different densities of digestible N. oculata. To evaluate larval performance, we examined larval morphogenesis and measured somatic growth of the carapace, starvation tolerance, development rate, and metamorphosis success. The food conditions significantly affected larval morphogenesis and growth. Additionally, we found large differences in many larval traits among the larvae hatched from different mothers. The food condition for achieving better survival differed among broods; thus, the optimal food conditions varied for larvae of different mothers. We conclude that seed-production success or failure depends largely on a match or mismatch between larval culture methods and characteristics conferred by the mothers used.

Growth and moulting of male adolescent snow crabs were investigated in a laboratory culture experiment. The moulting season of adolescents was separated into two groups of earlier and later, and they were regarded as normal and skip moulters, respectively. The existence of male snow crab skip moulters was first demonstrated in the Sea of Japan. Although the precise moulting season of the earlier moulter could not be revealed owing to the captive method, the later moulter is suspected to moult approximately 1 year after the earlier moulter. Earlier and later moulters were not different in growth of carapace width or chela height during the pubertal and terminal moult. Our moult and growth results of earlier and later moulters will be useful for predicting recruitment to legally fishable (>90 mm carapace width) or valuable (hard-shelled adult) populations of male snow crab in the Sea of Japan.

Population structure and demographic history of the Japanese Spanish mackerel Scomberomorus niphonius a highly piscivorous and migratory marine fish, were assessed using mitochondrial DNA control region sequences (n = 720) and microsatellite genotypes at five loci (n = 1331) for samples collected on Japanese coasts from 2001 to 2010. The population structure was panmictic and the haplotype and allele frequencies were temporally stable even during the recent recovery process. Demographic expansion was strongly supported throughout the Pleistocene, suggesting that the oscillating glacial and interglacial climate conditions in the Pleistocene had no substantial impact on the demographic history of S. niphonius.

Saddleback-like syndrome is one of the most frequently observed malformations in hatchery-reared red spotted grouper Epinephelus akaara. Saddleback-like syndrome is characterized by a V-shaped dorsal-profile depression behind the head region accompanied by deformities or misalignments of the first to fourth neural spines on the vertebral column and the first to fourth pterygiophores of the dorsal fin. Abnormal swim bladder inflation in several finfish species leads to malformations, particularly of the vertebral column. The present study examined the influence of swim bladder inflation on saddleback-like syndrome in hatchery-reared red spotted grouper. The incidence of saddleback-like syndrome increased as swim bladder inflation rate increased. Additionally, the incidence of saddleback-like syndrome among juveniles with inflated swim bladders was significantly higher than that among juveniles with uninflated swim bladders. The larval swim bladder is located just below the first to fifth vertebrae and the first to fifth dorsal spines, where saddleback-like syndrome occurs. Our results suggest that an inflated swim bladder increases the risk of saddleback-like syndrome in hatchery-reared red spotted grouper.

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.

We evaluated the thermal adaptations of embryos of 6 terrestrial hermit crab species in the family Coenobitidae (genera Birgus and Coenobita): B. latro, C. brevimanus, C. cavipes, C. purpureus, C. rugosus, and C. violascens. Embryos of each species were cultured in vitro at 6 dif- ferent temperatures (18 to 34°C) in artificial seawater to avoid air desiccation; the lower threshold temperatures for embryonic development were estimated using heat summation theory equa- tions. Additionally, partial effective cumulative temperatures (> lower threshold temperature) until hatching were determined for ovigerous females of each species cultured in containers. The relationships between the embryonic growth index values (relative area of the embryonic body vs. total embryo surface) and effective cumulative temperatures were expressed using cubic equa- tions. Lower threshold temperature was estimated to be 12.7 to 14.5°C. The effective cumulative temperature and egg incubation period estimates from the appearance of the embryonic body to hatching were higher in B. latro and C. brevimanus, followed by C. rugosus, C. cavipes, and C. violascens, and lower in C. purpureus, suggesting that C. brevimanus may retain an ancestral thermal adaptation trait for embryos, as in B. latro, which is considered the most ancestral species in the coenobitid phylogeny. Egg size varied among species but did not affect the thermal adap- tations of embryos. The lower effective cumulative temperature and shorter egg incubation period may be advantageous to producing broods during the shorter summer breeding season in C. pur- pureus, which has the northern-most geographical distribution.

Survival of the swimming crab, Portunus trituberculatus , during the post-larval period from the megalopal to the first crab stage was low compared with successive larval stages in seed production trials conducted in Japan. To clarify the cause for the low survival, we explored whether rotifers, Artemia , or phytoplankton have negative effects during this period. The effects of the causative factor on larval survival and morphology were verified, and measures to overcome low survival were investigated. We conducted three experiments. In experiment 1, larvae were reared with different types of food (rotifers or newly hatched Artemia ) with or without Nannochloropsis oculata supplementation during the late zoeal period (from the third to fourth zoeal stages). After moulting to megalopae, all larvae were fed newly hatched Artemia . The somatic sizes of the last stage (fourth stage) zoeae and megalopae were large, and developmental velocity was faster in the Artemia -fed groups than that in the rotifer-fed groups. However, Artemia feeding induced unviable and morphologically abnormal first-stage crabs with close-set eyes, regardless of Nannochloropsis supplementation. In experiment 2, third stage zoeae were reared to first stage crabs with variously treated Artemia such as newly hatched, 48 h starved, and Artemia enriched with commercially available digestible Nannochloropsis with physically broken cell walls to confirm the negative effects of feeding Artemia . Larvae reared with the newly hatched and starved Artemia containing lower eicosapentaenoic acid (EPA) content exhibited low survival (1.9–3.5%) from the megalopal to the first crab stage, whereas larvae reared with Artemia enriched with digestible Nannochloropsis containing higher EPA content achieved higher survival (40.7%). In experiment 3, newly hatched Artemia were cultured under various conditions such as supplementation with untreated Nannochloropsis , digestible Nannochloropsis , or without phytoplankton to investigate what caused the Artemia to starve. The treatments supplemented with untreated Nannochloropsis and without phytoplankton suppressed Artemia growth and resulted in total mortality 4 days after hatch. Supplementing with digestible Nannochloropsis maintained Artemia growth and resulted in higher survival, suggesting that early Artemia nauplii could not digest Nannochloropsis , which resulted in starvation. Our results indicate that Artemia starve in larval rearing water regardless of supplementation with Nannochloropsis ; however, Nannochloropsis are usually added to seed production tanks. Artemia starvation during the late zoeal period exerted a negative carry-over effect during the post-larval period. We recommend nutritionally enriching Artemia with EPA and supplementing larval rearing water with digestible Nannochloropsis during the late zoeal stage. Statement of relevance Improving larval rearing techniques for producing crablets.

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.

Terrestrial hermit crabs in the family Coenobitidae (genera Coenobita and Birgus) must migrate onto land after completing a pelagic larval stage in the ocean. Better knowledge of emigration behavior would assist in the conservation and management of coenobitid populations by helping identify and protect the habitats they need to complete their life cycles. We cultured laboratory-born individuals of five coenobitid species (Coenobita cavipes, C. purpureus, C. rugosus, C. violascens, and Birgus latro) from megalopae to early juveniles (first, second, and/or third crabs) in vessels containing seawater and a hard substrate, and analyzed their behavior and molting in conjunction with our published data for C. brevimanus. Our results confirm that the coenobitids migrated from sea to land at the megalopal stage. Megalopae and early juveniles tended to select shells based on their body size. Inland-dwelling coenobitids, such as C. brevimanus, C. cavipes, and B. latro, had a longer duration from landing to first molt and had a prolonged first crab intermolt period compared with those of the beach-dwelling coenobitids C. purpureus, C. rugosus, and C. violascens, probably because of the adaptive traits for migrating to inland habitats. Little burrowing behavior was observed by megalopae of B. latro, but they had a strong tendency to be cryptic under shelters. Additionally, megalopae and early juveniles of Coenobita spp. created and utilized burrows somewhat differently. Our results suggest that coenobitids require specific microhabitats for completing their early life stages in the wild. In particular, megalopae of B. latro may need structurally complex refuges to migrate from the sea.

Larvae of the swimming crab Portunus trituberculatus are traditionally cultured with rotifers, Artemia, and phytoplankton. However, abnormal morphology of last-stage zoeae caused by excessive nutritional intake, abnormal morphology of megalopae caused by indirect ingestion of phytoplanktons via rotifers during zoeal stages, and lack of essential nutrients due to starvation of Artemia cause mass mortality. To develop techniques addressing these issues simultaneously, we evaluated methods to prevent megalopal abnormalities while avoiding starvation of Artemia (experiment 1). Then, we evaluated the effects of Artemia feeding schedules on the occurrence of last zoeal abnormalities (experiment 2). In experiment 1, megalopal abnormality was prevented by rearing larvae with enriched Artemia supplemented with digestible Nannochloropsis, but without rotifers. However, the developmental rates were variable among individuals because of the large size of enriched Artemia for early zoeae, and last zoeal abnormality was induced because of excessive Artemia feeding, resulting in low survival. In experiment 2, newly hatched Artemia were only supplied during the first zoeal stage, and larvae were reared with low density Artemia and/or low salinity. These measures achieved high survival rate while suppressing the last zoeal abnormality. Our results suggest that P. trituberculatus larvae can be successfully cultured using only Artemia.

Although they are land dwellers, coconut crabs, Birgus latro , spend planktonic larval development in the sea and immigrate to the land as megalopae carrying gastropod shells. Better knowledge of settlement behavior and habitat requirements during the early life stages can assist in conservation of depleted coconut crab populations. Our objectives were to evaluate settlement behavior of coconut crab megalopae from 0 to 6 d post-metamorphosis (dpm), and determine the substrate preference (open sand, coral fragments, or brown algae) of 0–12 dpm megalopae. Early megalopae (0–3 dpm) were active swimmers during the night. The walking activity of naked megalopae was directly correlated with shell-inspection behavior during the day, peaking at 2–3 dpm. Almost all megalopae wore shells by 5 dpm and the walking activity of megalopae wearing shells was higher during the night than the day. Based on our observations, we hypothesize that megalopae migrate to the coast by nocturnal flood-tide transport and emigrate from the sea during the nocturnal full tidal phase to minimize predation risk. In the substrate choice experiment, early megalopae exhibited no preference for any substrata, and shell-less megalopae experienced the highest mortality, probably because of cannibalism. The survival rate plateaued at 9 dpm associated with an increase in the proportion of individuals wearing shells and of the onset of active habitat selection for complex substrata (coral fragments or brown algae). This suggests that shells and structural complex habitats are important for survival during the initial benthic phase of the coconut crab.

The moulting cycle and the time course of changes in body density from hatching to the end of the megalopal stage in snow crab (Chionoecetes opilio) larvae were investigated in laboratory-reared specimens. Morphological changes in the epidermis and cuticle were photographically documented to characterize the moult-cycle stages: A–B (postmoult), C (intermoult), D (premoult) and E (ecdysis). Moult-stage characteristics were based on a microscopical examination of integumental modifications, particularly of the telson. During stages A–C, the larval cuticle changed from a spongy structure to become conspicuously thicker and more solid in appearance. In stage D, the epidermis retracted from the cuticle and new setae and appendages were formed. The body densities of larval snow crabs were lowest just after moulting; they increased greatly during stage C, and then gradually increased to reach a plateau at 1.0897–1.0931 g cm−3 during stage D. Over the whole larval period, they have a density greater than that of ...

The occurrence of morphologically immature megalopae, which retain zoeal features such as dorsal spines and furcae of telson, is closely correlated with larval mass mortality during seed production of the swimming crab Portunus trituberculatus in Japanese hatcheries. To determine the cause of immature megalopal morphology, zoeae were reared with various supplementary schedules and density of diets (rotifer, Artemia and phytoplanktons including Chlorella vulgaris and Nannochloropsis oculata). In addition, to assess the relationship between immature morphology and endocrine control, the effect of causative dietary factor was compared with the effect of eyestalk ablation at various timing during zoeal development. Megalopal immature morphology was more distinct in Chlorella-supplemented groups than in Nannochloropsis-supplemented groups. High density Chlorella supplementation was associated with the highest incidence of immaturity and resulted in larval mass mortality. The premoult of the third zoeal stage was identified as a critical period at which Chlorella supplementation led to the highest incidence of immaturity. This critical period coincided with the critical period at which larval metamorphosis was regulated by the eyestalk neurosecretory system. Our results suggested that the occurrence of immature megalopal morphology under culture conditions is most likely caused by phytoplankton (especially, Chlorella) supplementation, which disrupts the endocrine regulation. On the basis of our results, we successfully prevented the occurrence of immature megalopal morphology in 500 L tanks by excluding the influence of phytoplankton before the critical period (i.e. discontinuing phytoplankton supplementation and supplying rotifer cultured with non-phytoplankton materials).

The effect of water temperature on the growth of juvenile snow crabs Chionoecetes opilio (Fabricius, 1788) was investigated in laboratory culture experiments. Laboratory-born juveniles were cultured from instar I to VIII at four temperatures (approximately 1, 3, 5 and 8°C). The growth indices (size increments at moulting in mm and in % of premoult carapace width) were significantly higher in crabs reared at 5°C than in those reared at other temperatures. The relationship between the mean temperature (T) and intermoult period (D) of each instar was described by the heat summation theory equation: D=K∕(T−α). The thermal constant K is the summation of the effective temperature for development (above the threshold temperature, α) up to a selected biological end point. The thermal constant tended to increase and the threshold temperature tended to decrease with increasing mean premoult carapace width of each instar, reaching asymptotes of 1573 day-degrees and −4.7°C, respectively. Size- and temperature-dependent growth models were developed for snow crab juveniles.