The sale of crayfish in the pet trade has increased in recent decades, and a substantial fraction of the world's entire range of crayfish species is available in the pet trade. The market for pet crayfish creates two major concerns: the potential for over exploitation of natural populations of crayfish to supply the pet trade, and the negative consequences resulting from the release of non-indigenous crayfish into natural habitats. The chain from the source of crayfish to the final owner can be lengthy, and each step in the supply chain needs to be studied by different methods. While there are often regulations intended to limit the trade of crayfish as pets, they differ widely from place to place and seem to have limited success in changing the behaviour of owners of pet crayfish.
Izuohshimaphryxus hoshinoi, a new genus and species of hemiarthrine bopyrid, is described on the basis of a single female specimen from the coastal waters of Izu-Ohshima Island, Sagami Sea, Pacific coast of central Japan. This bopyrid infests an anthozoan-associated shrimp, Ancylomenes speciosus (Okuno, 2004), attaching to the dorsal surface of the pleon. This new genus is most similar to Filophryxus Bruce, 1972 but is distinguished by a) the presence of pereopods on the concave side, b) number of lateral plates of the pleon, and c) absence of a pleotelson. This is the third identified species known to attach to the dorsal surface of the pleon of a caridean shrimp host.
The regulatory mechanisms of shell selection and occupation by hermit crabs can be determined by many factors such as competition, risk of predation, shell size, type and availability and also by physical damage. However, the relative importance among them has been scarcely studied. The aim of this study was to investigate the influence of predator, shell quality and size in shell exchanges and exploratory behaviors of Pagurus criniticornis. The experiments were carried out by placing a hermit crab with a naturally damaged shell in an arena with or without a caged predator (the narrowback mud crab, Panopeus americanus) and 10 empty shells. Concerning the male data and the shell exchange dependency on the factors of shell quality and predator presence, we suggest that individuals were sensitive to the predator presence when carrying a damaged shell. This data could represent a clear trade-off between the benefit of occupying a better shell and the imminent risk of predation. Considering that shells provide protection and that extremely damaged shells may increase the risk of predation, the exchange behavior is directly related to the increase in protection from predators, even if the exchange activity itself exposes the animal to a high predation risk for a short time.
Collecting Macrobrachium shrimps for abundance estimation is challenging, especially in high gradient, boulder dominated streams. The recent advent of digital cameras could change the situation by enabling previously under-used snorkel counting to yield verifiable data. The validity and efficiency of underwater movie recording for shrimp census were tested and compared with those of underwater shrimp net collection and sweeping in a field experiment (1–4 adult shrimps/m2). Total length estimates from the video footage were compared with caliper measurements. Detection was not affected by species, sex, or shrimp density. Movie recording and shrimp net collection yielded high and constant detection probability of adult shrimps (0.955 and 0.874), in contrast to sweeping (0.097). The movie recording had higher efficiency than the other two methods. For juveniles, only shrimp net collection was valid as an abundance indicator, with a detection probability of 0.338. Accuracy of total length estimates made from the video footage did not differ between species or sex and was highly correlated with the actual measurements by digital caliper. These results confirm that in adult Macrobrachium shrimps, the movie recording is valid for body size and quantitative abundance estimation, but not in juveniles.
Males of the hermit crab Pagurus middendorffii use their major cheliped in male–male contests during the reproductive season. This study examined whether autotomized major chelipeds were regenerated before, during or after the mating season. We reared males that were experimentally induced to autotomize just before the mating season (October). During the mating season (November), few males molted even if they had autotomized their major cheliped. In contrast, males initiated a molt at the end of and after the mating season, and most of the autotomized males regenerated their major cheliped before the end of the rearing period (December). This suggests that regenerated major chelipeds in this study affect events other than mating, particularly perhaps future shell acquisition associated with general activities such as predator avoidance, physiological tolerance and growth.
A new species of the genus Lipkemera Davie, 2010, is described from a submarine cave at Ie Island, Ryukyu Islands, Japan. Lipkemera iejima, new species, can be distinguished from congeners by the characters of ambulatory legs and the regionation of the dorsal surface of the carapace. The present study brings the number of Lipkemera species to five. A key to species of Lipkemera is also provided.
Life history and behavioral characteristics are described for a rare brackish-water crab, Ilyograpsus nodulosus (Sakai, 1983) (Family Macrophthalmidae), in Tanabe Bay, Wakayama, central Japan. Ovigerous females appeared from April through September, with the proportion of mature-sized females highest in June–July. Recruitment of juveniles occurred in July–September. Maturity was reached at several months of age, and longevity was estimated to be ≥ 1.5 years. The maximum carapace width of the females was 1.7-fold larger than that of males, indicating a female-biased size dimorphism. The sex ratio was not biased toward either males or females. Thus, this species is characterized by earlier maturation, shorter longevity, and female-biased size dimorphism, compared with other ocypodoids allied to the genus Ilyograpsus, such as species belonging to Macrophthalmidae and Camptandriidae. Egg size and number were not much different from those of other macrophthalmid species. Deposit and suspension feeding were observed. We did not observe crabs constructing burrows, as they hide in bottom mud. Males approached females without any courtship behavior prior to copulation. The copulative posture was female-uppermost. Five fighting behavioral elements were recognized during male-to-male fights, whereas only one fighting behavioral element was observed during female-to-female fights.
The spatial distribution, population structure and feeding behavior of the mole crab Hippa marmorata (Hombron & Jacquinot, 1846) was investigated on Iriomote-jima Island, Ryukyu Islands, in the Western Pacific region. Changes in the geographic distribution, body-size distribution, abundance, and vertical migration of mole crabs in response to the circatidal rhythms were examined by sampling sediments using a modified rake. Diel changes in the number of crabs exhibiting a pre-feeding posture to capture zooplankton were examined by visual counts. Mole crabs were more abundant at stations near the mouth of an inlet where terrestrial hermit crabs (Coenobita brevimanus) were previously observed to have released their larvae. The body-size distribution, measured as carapace length (CL), ranged from 5.3 to 20.3 mm in females and 4.1 to 12.1 mm in males. The pre-feeding posture was only observed at night, and increased and decreased in crab numbers observed with the flood (incoming) and ebb (receding) tides, respectively. Regardless of the tidal cycle, mole crabs were only collected in the swash zone, and the number of crabs collected was higher at night. The population structure and tidal migration characteristics of the mole crabs observed in this study closely correspond to the observations of previous studies. The temporal patterns observed in the adoption of pre-feeding posture among mole crabs may be an adaptation to feeding on the zooplankton that typically emerge at night.