We subjected the intertidal hermit crab, Pagurus samuelis (Stimpson, 1857), to various treatments to determine physiological responses of this species to the environmental stress of burial. Hermit crabs were buried with 6 cm of sediment and excavated at 2 h intervals up to a maximum of 12 h. Duration of burial and state (alive or dead) of the crab were analyzed for effects on lactate accumulation in hemolymph. Hermit crab weight, shell weight, weight ratio, lactate, and burial duration were analyzed for their influence on survival. As expected, lactate levels, as well as incidence of death, rose with duration of burial. Significant interaction, however, was also found between burial duration, crab state, and lactate concentration. There was a trend for lactate concentration to be low for surviving crabs, yet higher for dead crabs during shorter burial durations. Conversely and surprisingly, lactate concentrations were very high in surviving crabs, yet lower in dead crabs during long burial durations. Since some surviving crabs were able to develop very high lactate levels, we suggest that lactate buildup itself is unlikely to be the sole cause of death. Further studies are needed to identify factors affecting crab resilience during the stress of burial.
Occurrence pattern and reproductive ecology of a leucosiid crab, Pyrhila pisum were surveyed in tidal flats in Hakata Bay, Fukuoka, northern Kyushu, Japan. Size composition of each sex (male, juvenile and adult females) including carcasses was analyzed, and developmental stages of embryos and combination of mating pairs were checked. A mark-recapture experiment on adult crabs was conducted. In the study site, P. pisum was observed during 5 months only (late April to mid September). Carcasses were rarely found, and many adult crabs probably survived and migrated to the deeper subtidal zone after September. Four cohorts were detected in both sexes, and adults did not molt during their reproduction. Reproduction started after May in two large-sized adult cohorts. Female adults could spawn eggs three times. Two juvenile female cohorts were detected in May, and they joined reproduction after most of them had attained maturity by a puberty molt in late June and late July. Adult females copulated regularly in their hard-shell condition, and mating was observed even for ovigerous females.
Ovigerous females of Nerocila phaiopleura Bleeker, 1857 were collected from the body surface of young Pacific bluefin tuna, Thunnus orientalis (Temminck & Schlegel, 1844), cultured in Japan. This represents the first record of N. phaiopleura in finfish mariculture. The species is the third cymothoid isopod from maricultured fishes in Japan. The infected fish had a large hemorrhagic wound caused by N. phaiopleura at the attachment site. Thunnus orientalis is a new host of the isopod. No cymothoid infection has so far been reported from wild individuals of T. orientalis that swims at high speeds in the oceans, and the observed occurrence of N. phaiopleura on this fish species is regarded as unusual under confined mariculture conditions. The hosts and geographical distribution records of N. phaiopleura in Japan are reviewed.
An invasive freshwater shrimp of the genus Neocaridina Kubo, 1938 (Decapoda: Caridea: Atyidae) was collected from the Tomoe River of the Boso Peninsula, Tateyama City, Chiba Prefecture, eastern Japan. We compared the morphological characteristics and mitochondrial DNA sequence variation of the specimens with those of other Neocaridina species. In particular, we assessed the mitochondrial DNA region encoding the NADH dehydrogenase subunit 2 [ND2] gene and the region encoding the NADH dehydrogenase subunit 5 [ND5] gene. Our specimens are most likely to be Neocaridina davidi (Bouvier, 1904), a species native to mainland China. This species may have entered Japan through intentional disposal or accidental escape from aquaria.
Sedimentation and increasing temperature caused by human disturbances and global climate change are additive in their effects on coastal areas. To assess their influence on intertidal organisms, we studied the hermit crab, Pagurus samuelis, under acute temperature changes and shallow burial conditions. We applied three temperatures (5℃, 20℃, and 30℃) and two burial depths (3 cm and 6 cm) with a control at the surface (0 cm), and monitored survival, shell abandonment, and burial escape. Survival was primarily affected by temperature, with hermit crabs twice as likely to survive at 20℃ than at 30℃, and at 5℃ than at 30℃. The combined conditions of 30℃ and 6 cm were the least favorable for survival. Hermit crabs which abandoned their shells were more likely to survive burial at 20℃ and 30℃ than those retaining their shells. Fewer hermit crabs abandoned their shells when exposed to 5℃ than to 20℃ and 30℃. Crabs buried at 6 cm were 85.0% less likely to abandon shells than those buried at 3 cm, and heavier shells were less readily abandoned than lighter shells. Although overall, 35% of hermit crabs escaped burial to the sediment surface, hermit crabs buried in the combined conditions of 30℃ and 6 cm were significantly slower to reach the surface. Our results show that the combined stresses of temperature and burial can impact survival of hermit crabs in intertidal zones. While human activities, including dredging, industrial and domestic dumping, and coastal construction, result in relatively immediate increased inputs of sediment in coastal environments, climate change may endanger intertidal organisms, such as P. samuelis, living near their thermal tolerance over the long term, with both increasing temperature and sedimentation from more frequent storm events.
Aggressive behaviors are described for five species of the genus Ilyoplax (Dotillidae), I. pusilla (De Haan, 1835), I. formosensis (Rathbun, 1921), I. ningpoensis Shen, 1940, I. deschampsi (Rathbun, 1913), and I. tansuiensis Sakai, 1939, and the male/female ratios are compared relative to the sex ratio of the population. Aggressive behaviors were similar in all species. The main types of aggressive behaviors, including aggressive dash, aggressive wave, and wrestling, were common to the five species. The mutual aggression of wrestling was confined to male crabs in all five species. The frequencies of aggressive behaviors were higher in male crabs than in female crabs, suggesting male-biased aggressiveness. This may be reflected in the male-biased carapace and chela size dimorphisms observed in I. pusilla.
Two new species of the stenopodid shrimp genus Odontozona Holthuis, 1946 are described and illustrated based on material from several Indo-West Pacific localities, including Japan, Indonesia, Australia and Madagascar. Odontozona arbur sp. nov. is described on the basis of numerous specimens collected in Australia (Queensland, Western Australia), Indonesia, Japan and Madagascar. Odontozona stigmatica sp. nov. is described on the basis of a single specimen from Ishigaki Island, Ryukyu Archipelago, southern Japan. Odontozona arbur sp. nov. and O. stigmatica sp. nov. differ from all other species of the genus by a combination of morphological characters, mainly involving spination on the carapace and third pereopod, as well as sculpture of the pleon. This study increases the total number of species described in the genus Odontozona to 19, eight of them occurring in the Indo-West Pacific. An identification key to all species presently assigned to Odontozona is also presented.
The Norway lobster, Nephrops norvegicus, is a valuable and commonly exported European decapod crustacean, which experiences stress from point of capture and onward transport. Stressors such as air exposure duration (i.e. emersion period) and air temperature have been studied previously. We investigated whether mortality could be reduced by decreasing road vibrations during transport, and how physiological stress measurements were influenced in a transport simulation experiment, reflecting a typical short road journey along a supply chain. Baseline haemolymph samples were taken from lobsters sampled immediately after commercial capture using static traps (lobster pots). Individuals were emersed for one hour, either immobile or with continuous shaking; the latter to simulate conditions occurring during transport. Both treatments significantly increased Total Haemocyte Counts (THC) and serum glucose, lactate and ammonium concentrations compared to baseline animals. Individuals subjected to continuous shaking showed higher glucose and ammonium concentrations compared to individuals maintained immobile. We conclude that shaking appears to influence the physiological responses of N. norvegicus in addition to the effects of emersion alone, and the reduction of road vibrations (e.g. via simple cushioning) can reduce post-transport mortality.
Two new species of potamid freshwater crabs of the genus Chinapotamon Dai & Naiyanetr, 1994, are described from caves in Guangxi, southwestern China. Although obtained inside caves, C. dashiwei n. sp. does not show any cave-adapted morphological features, differing from congeners in the form of the carapace, structure of the male pleon and male first gonopods. Chinapotamon clarkei n. sp., on the other hand, has lost much of its body pigmentation, has conspicuously long ambulatory legs and the eyes are reduced with the cornea small. In these aspects, C. clarkei differs from all other Chinapotamon species and is the most stygobitic potamid currently known from China.