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Simple Summary: Boldness is a widely studied personality trait that is positively related to an individual's willingness to fight. To explore the agonistic behavior between female and male crabs with different degrees of boldness, we quantified the boldness of females and males using a behavior observation system and used the experimentally determined boldness and classification. The results showed that boldness affected the agonistic behavior between female and male swimming crabs, the fighting willingness and capacity of male crabs is higher than that of female individuals and is higher in bold crabs than in shy individuals. Energy reserves and metabolic rates may be one of the factors affecting the agonistic behavior in crabs and that the agonistic behavior resulted in significant changes in key energy metabolites. Individual differences in metabolism and agonistic behavior have been a key research area in evolution and ecology recently. In this study, we investigated the boldness of swimming crabs Portunus trituberculatus and explored the agonistic behavior between female and male crabs, specifically examining competitions between bold females vs. bold males (BF–BM), bold females vs. shy males (BF–SM), shy females vs. shy males (SF–SM), and shy females vs. bold males (SF_BM) and its relationship with energy metabolism. The main results revealed the following: There was no significant difference in boldness between females and males, while there were more bold individuals than shy in both females and males. Bold individuals initiated significantly more fights than shy individuals, and male initiators won significantly more fights than female initiators. The duration and intensity of fight between bold individuals was significantly higher than fights between shy individuals. For males, the concentration of glucose in the hemolymph was significantly higher in shy crabs than bold crabs, while there was no significant difference between shy and bold individuals in females. After fighting, the concentration of glycogen in claws was lower than that before fighting, and the concentrations of glucose and lactate in hemolymph were significantly higher after fighting than before. We found that the fighting willingness and ability were higher in male crabs than females and higher in bold crabs than shy. Fighting ability varied between sexes and was influenced by boldness and energy state. [ABSTRACT FROM AUTHOR]

Hard-shell-mating is the typical way that semi-terrestrial and terrestrial crabs copulate, when females reproduce with a hard carapace during the intermoult period and the couples have a brief or absent pre- and post-copulatory behaviour. For Gecarcinidae crabs there are few studies on reproductive behaviour, and are especially rare for isolated species, as in the genus Johngarthia. Here, we describe the mating behaviour of the endangered insular crab J. lagostoma endemic of the South Atlantic Ocean, with a focus on pre-, copulatory, and post-copulatory behaviours. Observations were made on 20 pairs in the field, with every female in intermoult. Accessory behaviours were absent, with copulation beginning after sexual recognition. After mating, there were no records of males guarding or embracing females. All couples had the female in an upper position and passive males, which do not react when other males are near the mating site. The size of the chelipeds and males were random and not determinant to mating. However, yellow crabs predominated (95%) in mating pairs and the linkage of colouration to sexual selection needs to be more elucidated because purple crabs are less frequent in the population and the lower representation in the couples can be an effect of this. Experimental studies are required to investigate sexual selection and the occurrence of the behaviour described herein at other locations. [ABSTRACT FROM AUTHOR]

Individual differences in metabolism and agonistic behavior have been a key research area in evolution and ecology recently. In this study, we investigated the boldness of swimming crabs Portunus trituberculatus and explored the agonistic behavior between female and male crabs, specifically examining competitions between bold females vs. bold males (BF–BM), bold females vs. shy males (BF–SM), shy females vs. shy males (SF–SM), and shy females vs. bold males (SF_BM) and its relationship with energy metabolism. The main results revealed the following: There was no significant difference in boldness between females and males, while there were more bold individuals than shy in both females and males. Bold individuals initiated significantly more fights than shy individuals, and male initiators won significantly more fights than female initiators. The duration and intensity of fight between bold individuals was significantly higher than fights between shy individuals. For males, the concentration of glucose in the hemolymph was significantly higher in shy crabs than bold crabs, while there was no significant difference between shy and bold individuals in females. After fighting, the concentration of glycogen in claws was lower than that before fighting, and the concentrations of glucose and lactate in hemolymph were significantly higher after fighting than before. We found that the fighting willingness and ability were higher in male crabs than females and higher in bold crabs than shy. Fighting ability varied between sexes and was influenced by boldness and energy state.

Crabs use burrows to prevent predation, environmental interference and shelter. The present study investigated the excavation behavior of the trichodactylid crab Dilocarcinus pagei, considering the biometric aspects of the burrows, the excavation time, the amount of bioturbation and the excavation behavior of the two sexes. The burrows of males had a mean diameter larger than the females, although the depth was similar for both sexes. Females had higher bioturbation than males, and showed enlargement in a camera format at the bottom, even closing the entrance of the burrows with a "plug" after their construction. Both the camera and the presence of the "plug" in the burrows of the females may be associated with reproduction. The presence of pellets observed at the entrance of burrows is associated with the cleaning of the pereiopods by crabs after the excavation. The sequence of behaviors for the construction of the burrows is described in detail, contributing to the knowledge about the biology and ecology of freshwater crabs of the Amazon. [ABSTRACT FROM AUTHOR]

• We selected a candidate molting biomarker, GlcNAc-6-P, of the E. sinensis. • We identified substances in the molting fluid by metabolomics techniques. • The GlcNAc-6-P is associated with the catabolism of chitin. • Non-molting crabs locate molting crabs by sensing molting chemical cues. Under high-density culture, cannibalism occurs frequently during the molting of the Chinese mitten crabs Eriocheir sinensis , resulting in a large reduction in production. We found that the leakage of molting fluid from sexually immature crabs informs conspecifics that they are in a molting process. This hypothesis was verified through metabolomics analyses combined with behavioral experiments. The GlcNAc-6-P was identified as a molting biomarker from the differential metabolites by non-targeted metabolomics. In addition, we found that the concentration of GlcNAc-6-P in the molting fluid was significantly higher than other molting metabolites at different molting stages, reaching 5.84 μmol L−1, indicating that the molting fluid was the source of GlcNAc-6-P. Moreover, the behavioral experiments showed that crabs were actively approached to high concentrations of GlcNAc-6-P (1 μmol L−1), but had no obvious choice tendency at different concentrations of UTP, 20-HE and low concentrations of GlcNAc-6-P (0.1 μmol L−1, 0.01 μmol L−1) compared with the control groups. In conclusion, that E. sinensis by sensing the concentration change of GlcNAc-6-P can locate the source of GlcNAc-6-P release and actively approach the high concentration GlcNAc-6-P area and attack the molting crab, causing cannibalism. Blocking the reception pathway of molting chemical cues in E. sinensis , thereby preventing the perception of signals originating from conspecifics' molting in the vicinity, could lead to a reduction in cannibalistic behavior and an increase in overall production. Additionally, this method presents a prospective solution for addressing cannibalism in other crustacean species where such behavior is prevalent. [Display omitted] [ABSTRACT FROM AUTHOR]

Horseshoe crabs are harvested by the biomedical industry in order to create Limulus amebocyte lysate to test medical devices and pharmaceutical drugs for endotoxins. Most previous studies on the impacts of the biomedical bleeding process on horseshoe crabs have focused on mortality rates and sublethal impacts in the laboratory. In this study, we investigated the effects of the bleeding process on the behavior of horseshoe crabs after they had been released back into their natural environment. A total of 28 horseshoe crabs (14 control and 14 bled) were fitted with acoustic transmitters and released into the Great Bay Estuary, New Hampshire, during the spring of 2016. The acoustic tags transmitted information about the activity and depth of each animal, and these data were logged by an array of passive acoustic receivers. These data were collected from May to December 2016 and from March to October 2017. Bled animals approached mating beaches less than control animals during the first week after release, with the greatest differences between bled and control females. Bled animals also remained significantly deeper during the spawning season than control animals. However, overall, bled and control animals expressed similar biological rhythms and seasonal migrations. Thus, it appears as if the most obvious impacts of the bleeding process take place during the first one to two weeks after crabs are bled. [ABSTRACT FROM AUTHOR]

The freshwater anomuran crabs of the genus Aegla are widespread throughout lakes and rivers in central and southern Chile. They form an important component of the benthic fauna, because the species of the genus are shredders of organic debris and also make an important prey for native and introduced fishes. Nevertheless, the ecology of this genus has been poorly studied in lakes in comparison to rivers. The aim of the present study was a description of the spatial pattern of distribution of an Aegla rostrata population from the littoral zone of Pullinque Lake, in the north of Chilean Patagonia. The results revealed a low density (1.0 ± 0.8 ind/m2), that had a uniform pattern, and has a positive binomial distribution. The results would indicate that the studied species would have territorial behaviour that would be associated with interspecific resource competition. The observed results would agree with observations for the benthic zones in Chilean Patagonian lakes, where Aegla would show territorial behaviour. [ABSTRACT FROM AUTHOR]

The article offers information on the study of Brachyuran crabs or Palicoides whitei. Topics discussed include information on biological family that is Palicidae Bouvier; information on the marine environment habitat of Brachyuran crabs; and behavioral study of Brachyuran crabs. An overview of taxonomy of Brachyuran crabs is also presented.

We studied the effects of claw regeneration on male waving rate and burrow characteristics (i.e., important mate choice criteria) by examining the waving rates and burrow characteristics (diameter, total and horizontal lengths, depth, volume, maximum width, entry and burrow angles, and presence and location of chambers) of large-sized original-clawed males (OCMs) and regenerated-clawed males (RCMs) of Austruca perplexa (H. Milne Edwards, 1852). Female burrows were also examined. The results showed that female burrows were smaller than male burrows, with no chamber and, thus, female burrows are not used for breeding; however, 80% of RCM burrows, and 65% of OCM burrows, had chambers. Other characteristics were not different between RCM and OCM burrows, except for maximum width, which was larger in RCM burrows. The waving rates of OCMs and RCMs were not different. Our results indicate that claw regeneration do not have detrimental effects on male waving rate and burrow characteristics. [ABSTRACT FROM AUTHOR]

Polychaetes and burrowing crabs are widely distributed in intertidal soft bottom environments, playing an important role in structuring infaunal assemblages through trophic and non-trophic interactions such as bioturbation. In southwestern Atlantic (SWA; 37°40′S, 57°23′W) intertidal mudflats, the polychaetes Laeonereis acuta and Neanthes succinea coexist with the burrowing crab Neohelice (Chasmagnathus) granulata. N. granulata and L. acuta strongly modify the sediment characteristics at different spatial scales, changing the infaunal assemblages and probably affecting feeding mode of N. succinea , which could prey upon L. acuta . Here, we experimentally evaluated the effects of constant densities of L. acuta and N. succinea on the benthic species assemblages and sediment organic matter (OM) content in two contrasting scenarios of crab bioturbation: inside and outside crab beds. We found that (1) both polychaetes did not affect the mean density of other macrofaunal organisms neither the meiofauna in general, but L. acuta modifies the abundance of specific groups such as foraminiferans; (2) polychaetes produced changes in meiofaunal spatial distribution probably by adding habitat heterogeneity; and (3) no evidence of predation of N. succinea on L. acuta were observed. Additionally, the variable effects of polychaetes on chlorophyll a nd OM content showed that they were species-specific and also modified by crab bioturbation. Moreover, effects of crab bioturbation on primary producers, quality and content of OM, and on some macro and meiofaunal organisms were found. Our results suggest that the effects of L. acuta and N. succinea on benthic species and OM content are mostly species-specific and, with regard to food sources (OM content and microphytobenthic biomass), strongly modified by larger scale crab bioturbation. [ABSTRACT FROM AUTHOR]

Studies on brachyuran burrowing crabs have shown a relationship between the dimensions of the burrow opening and the size of the constructor. Estimating specimen size using this relationship may nevertheless be biased since individuals of different species and sizes are commonly found using the same burrow. We describe the use of an endoscopic camera to estimate the carapace width (CW) of decapod crustaceans within their burrows, using Ocypode quadrata (Fabricius, 1787) (Brachyura, Ocypodidae) as a model. Videotapes of crabs were filmed inside an artificial burrow using an endoscopic camera fitted with a fixed rod. The length of the carpi and propodi of the third and fourth pereiopods and CW were measured in 35 individuals using a digital caliper. We used Paint.net to measure the lengths in pixels of the pereiopods and converted them to millimeters. The Pearson’s correlation coefficient indicated a high correlation between caliper-measured CW and the CW estimated by the length of the perieopod articles as measured by a caliper (R2 minimum = 0.97, P < 0.01) and pereiopods images (R2 minimum = 0.97, P < 0.01). Our results show that images obtained with endoscopic cameras are feasible for effective and non-destructive estimation of the size of brachyuran crabs living inside their burrows. [ABSTRACT FROM AUTHOR]

Portunid crabs characteristically undertake soft-shell-female mating, with extensive pre- and post-copulatory guarding of the female. We herein record hard-shell-female mating in the portunid Charybdis japonica (A. Milne-Edwards, 1861) in New Zealand. Mating pairs were recorded in 2014 and 2015 between August and December inclusive, with peak mating in late winter/early spring. Copulation in C. japonica was prolonged, lasting between 180 to 270 min, with no pre- or post-copulatory guarding being observed. Among members of the family Portunidae, hard-shell-female mating has only been documented in the subfamily Thalamitinae, with C. japonica the fifth species documented to utilise this mating strategy. Further investigations are warranted to determine the extent of hard-shell-female mating within other subfamilies of Portunidae. [ABSTRACT FROM AUTHOR]

Studies on relative growth and sexual maturity are important to understand the reproductive biology of a species. The aims of this study were to determine the relative growth and to estimate the size of Panopeus occidentalis at morphological sexual maturity, as well as to confirm whether this species demonstrates heterochely or handedness. Individuals were collected every two months from March 2013 to July 2014 in the intertidal estuarine zone of Cananeia, São Paulo, Brazil. The following measurements were taken: carapace width (CW), carapace length (CL), right and left cheliped propodus length (CPL), right and left cheliped propodus height (CPH), right and left cheliped propodus width (CPW), abdomen width (AW), and first pleopod length (FPL). The morphometric relationship used to estimate the size at morphological sexual maturity were CW vs. AW for females and CW vs. FPL for males; these comparisons yielded estimated CW values of 15.60 mm and 16.67 mm, respectively. Heterochely was observed but handedness was not present. The species has a major cheliped on one side, but the side is not constant. This study provides the first insights on the relative growth, sexual maturity, heterochely, and handedness on a population of P. occidentalis in a conserved area. [ABSTRACT FROM AUTHOR]

Looming-sensitive neurons (LSNs) are motion-sensitive neurons tuned for detecting imminent collision. Their main characteristic is the selectivity to looming (a 2D representation of an object approach), rather than to receding stimuli. We studied a set of LSNs by performing surface extracellular recordings in the optic nerve of Neohelice granulata crabs, and characterized their response against computer-generated visual stimuli with different combinations of moving edges, highlighting different components of the optical flow. In addition to their selectivity to looming stimuli, we characterized other properties of these neurons, such as low directionality; reduced response to sustained excitement; and an inhibition phenomenon in response to visual stimuli with dense optical flow of expansion, contraction, and translation. To analyze the spatio-temporal processing of these LSNs, we proposed a biologically plausible computational model which was inspired by previous computational models of the locust lobula giant motion detector (LGMD) neuron. The videos seen by the animal during electrophysiological experiments were applied as an input to the model which produced a satisfactory fit to the measured responses, suggesting that the computation performed by LSNs in a decapod crustacean appears to be based on similar physiological processing previously described for the LGMD in insects. [ABSTRACT FROM AUTHOR]

We examined the effects of mudballs around burrows and of sex on burrow characteristics (shape, diameter, length, depth and volume) in an underground mating fiddler crab species, Austruca annulipes (H. Milne Edwards, 1837). We investigated 35 burrows with mudballs (males: 20; females: 15) and 34 burrows without mudballs (males: 16; females: 18), and measured their burrow characteristics. Results showed that burrow characteristics did not differ between burrows with and without mudballs. Males built larger-sized burrows with greater volumes, and had more mudballs than females. Crabs built J-, I-, L-, S- and U-shaped burrows, with higher numbers of J-shaped burrows in males, and higher numbers of I-shaped burrows in females. J-shaped burrows were larger with greater volumes, and had more mudballs than I-shaped burrows. For burrows with mudballs, mudball numbers were positively associated with burrow characteristics. This indicates that fiddler crab burrow characteristics are affected by sex, not by the production and presence of mudballs. [ABSTRACT FROM AUTHOR]

Although numerous aquatic and terrestrial species adorn their surface with items secured from their surroundings, termed decorating, the physical and environmental factors that drive this behavior are often unclear. One of the best-known examples of this phenomenon are the decorator crabs (Majoidea), with almost 75% of species known to decorate. Here, we examined patterns of decorating in a coral reef-associated majoid, Camposcia retusa, to identify what factors determine patterns of, and investment in, decorating. Observations of natural decoration patterns indicate this species primarily decorate with sponges, fleshy and filamentous algae, and detritus. Decorations were primarily distributed on the carapace and hind walking legs which may reflect exoskeleton morphology. However, decoration cover did not decline with size, as is observed in some other majoid species, suggesting the factors driving decoration investment remain consistent throughout growth stages. From behavioral experiments, we determined that nonuniform decorating is a result of active selection, with crabs preferentially decorating their hind legs and carapace, with only small items placed on the carapace. Decorating in C. retusa appears to function primarily as an antipredator response, with crabs decorating at higher rates when access to shelter is limited. This study is the first to quantify the decorating habits of C. retusa and suggests that behaviorally-mediated decorating has a primary antipredator function. This study also highlights the value of manipulative behavioral experiments as a tool for assessing the behavioral mechanisms that drive decorating in animals. [ABSTRACT FROM AUTHOR]

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Biotic interactions can structure ecological communities and influence ecosystem functioning. As ecosystem engineers and filter feeders, bivalves often have disproportionately large effects on ecosystem functioning. They also utilize numerous morphological and behavioral responses to reduce predation, which can include changes in their filtration rates. To test the response of Crassostrea virginica filtration rates to the presence of predators, juvenile and adult oysters were separately exposed to varying types of predation risk from Callinectes sapidus and Panopeus herbstii in outdoor mesocosms. Water column chlorophyll a concentrations and crab behavior were measured over the duration of the experiment. Predation risk had no effect on oyster reef drawdown of chlorophyll a, which suggests that this important ecosystem function of oyster reefs is not mediated by behaviorally induced predator effects. Therefore, efforts to model how oyster predators influence filtration rates and associated ecosystem services should focus primarily on the factors that influence oyster mortality rather than predator effects on oyster behavior. [ABSTRACT FROM AUTHOR]

The taxonomy of Daldorfia spinosissima (A. Milne-Edwards, 1862) and D. triangularis Sakai, 1974, two large and rarely reported parthenopid species, is discussed. The taxonomy of the two species had been confused until Tan & Ng (2007) argued that both were valid taxa. The availability of fresh species material allowed direct comparisons to be made and the two taxa could, in fact, be separated by a good series of characters: carapace shape, spination on carapace surfaces and chelipeds, rostral form, shape of proepistomal spine, proportions of the third maxilliped ischium, overall structure of the chelipeds, relative lengths of the ambulatory merus, shape of the anterior thoracic sternal depression, and proportions of the male pleon, as well as structure of the male first gonopod. [ABSTRACT FROM AUTHOR]

Though cryopreservation of some invertebrate embryos was successful, the cryopreservation of crustacean embryos has not yet been reported. On the basis of previous study, a single vitrifying cocktail (Code A: 30% propanediol and 20% dimethyl formamide) was selected as a cryoprotectant from six kinds of vitrifying solutions to cryopreserve E. sinensis embryos. The cleavage stage, the gastrula, the pre-nauplius, and the first zoea stage embryos were serially acclimated in 25, 33, 50, 67 and 100% vitrifying solution A for 6 min. Embryos were acclimated for 1 min on the 20 cm liquid nitrogen (LN2) layer, and then plunged into liquid nitrogen. After storage for several minutes in LN2, straws containing frozen embryos were acclimated for 1 min on the 20 cm liquid nitrogen (LN2) layer, then quickly removed from LN2. For thawing, straws were immersed quickly for 1 min in a water bath at 37°C, then carefully washed with 0.25 mol/l sucrose and were then incubated with 15 ppt seawater in a Petri dish at 25°C. The survival rate in the vitrifying solution differed for embryos in different stages of development, and the survival rate of different stage embryos declined with the increase of acclimation time in code A vitrifying solution. The survival rate of pre-nauplius stage embryos did not significantly differ when the embryos were washed for 5, 10, 15, or 20 min with 0.25 mol/l sucrose after thawing. There was no survival after either cleavage stage embryos, or gastrula stage embryos were frozen. Eight pre-nauplius stage embryos survived and the survival rate was 9.3 ± 2.5%, but subsequently the embryos died at the fourth day. Seven first zoea stage embryos survived, and the survival rate was 11.3 ± 3.6%, one frozen-thawed embryo hatched at the seventh day. We conclude that cryopreservation of E. sinensis embryos by vitrification is feasible. [ABSTRACT FROM AUTHOR]

A new species of lowland freshwater crab of the family Gecarcinucidae, Salangathelphusa peractio, is described from Langkawi, an island off the northwestern coast of peninsular Malaysia. Salangathelphusa peractio sp. n. can be separated from S. brevicarinata (Hilgendorf, 1882) in having a proportionately broader external orbital tooth, a distinctly concave posterolateral margin, and the terminal segment of the male first gonopod is not distinctly bent laterally outwards; and from S. anophrys (Kemp, 1923) by its more quadrate carapace and the terminal segment of the male first gonopod possessing a relatively longer and less curved distal part. This is sixth wholly freshwater brachyuran species known from the island. [ABSTRACT FROM AUTHOR]

The mating systems of symbiotic crustaceans vary broadly, ranging from monogamy to polygamy to promiscuity. This disparity in mating systems coupled with wide differences in host ecology provides opportunities to study the effect of environmental conditions on the social behavior of marine organisms. In this study, we tested the prediction that symbiotic crustaceans inhabiting relatively large and abundant host species are promiscuous rather than monogamous. The host traits above constraint host monopolization and favor host-switching behaviors by males individuals and, thus, ultimately drive promiscuity as a mating system in symbiotic crustaceans. As a model system we used Dissodactylus crinitichelis, a small 'pea-crab' that inhabits the relatively large and abundant sand dollar Encope emarginata. We described the population distribution of D. crinitichelis at two intertidal localities in Sergipe, Brazil, and conducted laboratory experiments to infer the mating system of this species. Dissodactylus crinitichelis inhabit sand dollars as adult heterosexual pairs more frequently than expected by chance alone, but these heterosexual pairs did not exhibit size-assortative pairing. Sexual dimorphism was reversed in D. crinitichelis, with males attaining smaller average body sizes than females but exhibiting more elaborated weaponry (male > female claws). These findings disagree with expectations for monogamous symbiotic crustaceans. Laboratory experiments demonstrated that male and female crabs switch among host individuals rather frequently and heterosexual pairs retrieved from the field did not remain together for long times. Our results argue against social monogamy and in favor of promiscuity in D. crinitichelis. Our study supports the notion that host abundance and large body size (relative to that of symbiotic guests) favor promiscuity in symbiotic crustaceans. [ABSTRACT FROM AUTHOR]

Claw-only crab fisheries are often marketed as renewable because crabs are returned to the water after declawing to regenerate claws and re-enter the fishery. The challenge of managing a claw-only fishery for stone crabs ( Menippe spp.) is compounded by varying regulations throughout their range that include the number of claws harvested from a crab and use of a seasonal closure to protect spawning females. We conducted mark-recapture studies to examine crab responses to claw removal in the field and compared claw handedness and type (crusher, intermediate, pincer) in a wild population to commercial landings to examine compliance with fishery regulations in a one-claw fishery with no seasonal closure. Declawed crabs were recaptured less frequently than control crabs, particularly if claw removal created large wounds. Control crabs were more commonly recaptured within one month of tagging and declawed crabs recaptured one to three months after tagging, suggesting that declawed crabs were less mobile or less motivated to feed initially after claws were harvested and that, over time, intact crabs left the study area. Crabs with fishery-related, regenerated claws comprised 3% of crabs with legal claws. Claw type ratios in a limited assessment of the commercial catch most closely reflected expected ratios consistent with a two-claw fishery, indicating that voluntary adherence to current one-claw fishing regulations is not universal. In fisheries needing better protection of spawning stock, a seasonal closure on fishing could be instituted to ensure better protection of spawning. [ABSTRACT FROM AUTHOR]

Prey exposed to predators with different hunting and feeding modes are under different selective pressures, therefore it is expected that they should exhibit plastic and adaptive antipredator responses according to current risks. The hermit crab Calcinus californiensis faces two contrasting predators, the shell peeler Arenaeus mexicanus that hunts by active searching and the shell breaker Eriphia squamata that hunts by ambush. In order to discover whether C. californiensis displays plastic responses depending on the type of predatory challenge, we examined the shell size preference, the hiding time, and the escape velocity of hermit crabs in the presence of chemical cues from a shell peeler, a shell breaker, and a control. We also examined the role of shell fit on the escape velocity of the hermit crabs in natural tidal pools. Crabs chose shells with a loose fit (relatively large shells) in the presence of chemical cues from the shell peeler Arenaeus and shells with a tight fit when exposed to cues from the shell breaker Eriphia. The hermit crabs hid for shorter times and moved away faster from Eriphia than from Arenaeus stimulus. The use of a tight shell favours faster movement away from the shell breaker (pre-capture strategy), but prevents the crab retracting deeper inside the shell, increasing the risk of be eaten by the shell peeler once captured. Hence, the use of loose shells that protect the crab from the shell peeler hinders fast escape. This study shows specific and plastic antipredatory responses to contrasting predators, each bringing adaptive benefits at different levels of the predator sequence. [ABSTRACT FROM AUTHOR]

Non-random mating, especially size-assortative mating, has been observed in animals, including brachyuran crabs. Studies on the mating behaviour and mate selection of mud crabs of the genus Scylla De Haan, 1833 (family Portunidae), however, is limited. We investigated the possibility of assortative mating by size in three sympatric species of Scylla in Malaysia, the effect of male sizes on mating success and the difference in the body size of the mating pairs. Larger males mated with larger females and smaller males with smaller females. Males in all guarding pairs (from field populations) and mating pairs (in captivity) were larger compared to their respective female partners. Mating success was not affected by the difference in male-size classes in the three species. The proportion of size difference between mating pairs in captivity was largest in S. olivacea (Herbst, 1796), followed by S. tranquebarica (Fabricius, 1798) and S. paramamosain Estampador, 1949, and increases with male-size class. Strong size-assortative mating was observed in all three species. [ABSTRACT FROM AUTHOR]

Behavioural decisions are often context-dependent, where information from immediate experience is incorporated into an individual's decision-making, particularly in complex environments. To test whether such mechanism is adopted by foragers in heterogeneous environments, we investigated the foraging behaviour of the deposit-feeding sand-bubbler crab, Scopimera intermedia. An individual-based model was constructed, based on an optimal-patch selection criterion, which implicitly assumed that individuals adjust foraging decisions based on immediate past experience. The model's predictions were tested on the shore by manipulating the location of food patches, where the crab showed a strong context-dependent foraging pattern. When resources were randomly distributed, the crab responded by spending 56% of time in enriched patches compared with only 28% in the same area when patches were composed of natural sediments. Shore manipulations varying resource distribution supported the underlying principles of the model mechanism, and highlighted the benefits of such a strategy in heterogeneous environments such as intertidal sediments where food resources vary at different spatial and temporal scales. The proposed model therefore provides a mechanistic process, based on optimal foraging, to predict foraging decisions and movement patterns of animals feeding in heterogeneous landscapes. [ABSTRACT FROM AUTHOR]

Predation can strongly influence community structure and ecosystem function, so the loss of key predators can have dramatic ecological consequences, unless other predatory species in the system are capable of playing similar ecological roles. In light of the recent outbreak of sea star wasting disease (SSWD) and subsequent depletion of west coast sea star populations, including those of the keystone predator Pisaster ochraceus, we examined whether large mobile crabs could play a role as predators on mussels (Mytilus californianus) on a rocky shore in Northern California. Using a combination of sea star removal and predator exclusion cages we found that mussel mortality was 43–294 times greater in uncaged treatments versus caged treatments. Mortality on uncaged mussels at low tidal elevations was due to predation by large mobile crabs (Cancer productus and Romaleon antennarium); confirmed by the presence of mussel shell fragments and documented attacks on wax snail replicas. Laboratory feeding assays indicated that crabs, on a per unit biomass basis, can consume almost twenty-five times as many mussels per day than sea stars, which together with the results of our field experiment, suggest that large predatory crabs could play an important role in maintaining ecosystem function through their predation on mussels on rocky shores where P. ochraceus are rare, absent, or have been depleted by SSWD. [ABSTRACT FROM AUTHOR]

Predator avoidance and prey capture are among the most vital of animal behaviors. They require fast reactions controlled by comparatively straightforward neural circuits often containing giant neurons, which facilitates their study with electrophysiological techniques. Naturally occurring avoidance behaviors, in particular, can be easily and reliably evoked in the laboratory, enabling their neurophysiological investigation. Studies in the laboratory alone, however, can lead to a biased interpretation of an animal's behavior in its natural environment. In this Review, we describe current knowledge - acquired through both laboratory and field studies - on the visually guided escape behavior of the crab Neohelice granulata. Analyses of the behavioral responses to visual stimuli in the laboratory have revealed the main characteristics of the crab's performance, such as the continuous regulation of the speed and direction of the escape run, or the enduring changes in the strength of escape induced by learning and memory. This work, in combination with neuroanatomical and electrophysiological studies, has allowed the identification of various giant neurons, the activity of which reflects most essential aspects of the crabs' avoidance performance. In addition, behavioral analyses performed in the natural environment reveal a more complex picture: crabs make use of much more information than is usually available in laboratory studies. Moreover, field studies have led to the discovery of a robust visually guided chasing behavior in Neohelice. Here, we describe similarities and differences in the results obtained between the field and the laboratory, discuss the sources of any differences and highlight the importance of combining the two approaches. [ABSTRACT FROM AUTHOR]

In a previous study, lethal effects of mudskipper (predator) presence were detected in the mangrove brachyuranParacleistostoma depressumbut notHaberma nanum. In addition, these effects were sex specific (male: non-significant; female: significant), suggesting differences in anti-predator behaviour. To validate this, predator avoidance strategies of the two prey species were investigated for the variables ‘species’ and ‘sex’. Ex situ responses of 40 crabs (10 per sex per species) to a mudskipper model were video-recorded. Three stimuli were given in the sequence of (A) upper torso appearance, (B) full body appearance and (C) lunge towards crab. Innate behaviour to any innocuous signal was ruled out by replacing the mudskipper model with a rectangular block. Lastly, predator recognition capabilities in terms of shape and presence of eyes were tested using five models with increasing similarity to the predator model.P. depressumandH. nanumshare the same suite of observable anti-predatory behaviours: “freeze”, “sit” or “run”. However, varied strategies were observed. Instead of flight,P. depressum“sit”, and reacted most notably in the last stimulus. In contrast,H. nanumreacted early in the onset of impending threat with “run”, with diminished responses despite the increase in signal strength. Contrary to prediction, the factor ‘sex’ was not statistically significant in either species. Predator recognition capabilities were ascertained in both prey species, as behaviours were different after the predator model was replaced.H. nanumdisplayed greater sensitivity for threat perception by withholding the flight behaviour when uncertain. This keen sense for threat recognition coupled with its flight strategy may be key to explaining the exclusion ofH. nanumfrom the predator’s diet. [ABSTRACT FROM AUTHOR]

Sexual dimorphism is common in species where one sex fights for access to the other sex, or one sex displays to attract the other sex for mating. We show that in the dotillid crab Scopimera globosa (De Haan, 1835) there is strong sexual dimorphism with males having relatively larger chelae (claws) than females. We also found that males had relatively longer walking legs (pereiopods) than females, a pattern previously shown in a few brachyuran crabs. This species exhibits five distinct aggressive behaviors and males predominantly engage in aggressive interactions. Unlike other brachyuran crabs, males do not grasp each other with their chelae during fights and chela size was not a determinant of winning such interactions. The most escalated fight, the wrestle, involves the raising of the walking legs, and leg length was a strong predictor of fighting success. We suggest that the sexual dimorphism in leg length has evolved in response to the use of the legs in determining fighting success. [ABSTRACT FROM AUTHOR]

Shell fragmentation patterns that result from attacks by durophagous predators on hard-shelled marine invertebrates are a rich source of indirect evidence that have proved useful in interpreting predation pressure in the fossil record and recent ecology. The behaviour and effectiveness of predators are known to be variable with respect to prey size. It is less well understood if variable predator-prey interactions are reflected in shell fragmentation patterns. Therefore, we conducted experimental trials to test the behavioural response of a living crab, Carcinus maenas, during successful predatory attacks on the blue mussel Mytilus edulis on two prey size categories. Further, we examined resultant shell fragments to determine whether specific attack behaviours by C. maenas could be successfully deduced from remaining mussel shells. In contrast to previous studies, we observed no significant differences in attack behaviour by the predators attributable to prey size. In most experimental predation events, crabs employed an ad hoc combination of five mechanisms of predation previously described for this species. We identified seven categories of shell breakage in predated mussels, but none of these were unambiguously correlated with specific attack behaviour. Combined attack behaviours may produce shell breakage patterns that have previously been assumed to be attributable to a single behaviour. While specific patterns of shell breakage are clearly attributable to durophagy, the results of this study provide important insights into the limitations of indirect evidence to interpret ecological interactions. [ABSTRACT FROM AUTHOR]

New England salt marshes are susceptible to degradation and habitat loss as a result of increased periods of inundation as sea levels rise. Increased inundation may exacerbate marsh degradation that can result from crab burrowing and foraging. Most studies to date have focused on how crab burrowing and foraging can impact the dominant low marsh plant species, Spartina alterniflora . Here we used a mesocosm experiment to examine the relationship of foraging and burrowing activity in two dominant New England crab species, Sesarma reticulatum and Uca pugilator , and the combined effect of inundation, on the dominant high marsh plant species Spartina patens using a 3 × 2 factorial design with three crab treatments ( Sesarma , Uca , control) at two levels of inundation (low, high). Plants were labeled with a nitrogen (N) stable isotope tracer to estimate plant consumption by the two crab species. At both levels of inundation, we found that S. reticulatum had a significant negative impact on both above- and below-ground biomass by physically clipping and uprooting the plants, whereas U. pugilator had no significant impact. Low inundation treatments for both crab species had significantly greater aboveground biomass than high inundation. Stable N isotope tracer levels were roughly the same for both S. reticulatum and U. pugilator tissue, suggesting that the impact of S. reticulatum on S. patens was not through consumption of the plants. Overall, our results suggest the potential for S. reticulatum to negatively impact marsh stability, and that effects of crab foraging behavior may be heightened by increased inundation. [ABSTRACT FROM AUTHOR]

Marine and estuarine crabs brood attached eggs, which hatch synchronously releasing larvae at precise times relative to environmental cycles. The subtidal crabDyspanopeus sayihas a circadian rhythm, in which larvae are released within the 4-h interval after the time of ambient sunset. Previous studies demonstrated that the rhythm can be entrained by the light:dark cycle. Since subtidal crabs are also exposed to temperature fluctuations, an unstudied question was whether the circadian rhythm could be entrained by the diel temperature cycle. To answer this question, ovigerousD. sayiwere entrained in darkness to 2.5, 5, and 10 °C temperature cycles that were reverse in phase from the ambient temperature cycle. After entrainment, larval release times were monitored in constant conditions of temperature and darkness with a time-lapse video system. The effectiveness of a temperature cycle to shift the timing of larval release increased as the magnitude of the temperature cycle increased and as crabs were exposed to increasing numbers of entrainment cycles. However, entrainment to a 10 °C cycle only lasted 2 days in constant conditions. When crabs were entrained to a light:dark vs. a 10 °C temperature cycle, the light:dark cycle was dominant for entrainment. Nevertheless, ovigerous crabs do sense temperature cycles and in areas where daylight is too low for entrainment, temperature cycles can be used to regulate the time of larval release. [ABSTRACT FROM AUTHOR]

An emerging focus of behavioural ecology is to determine the driving forces behind animal personalities. While numerous theories have been proposed to explain these behavioural variations, empirical studies on this subject remain lacking. Here, we test ecological theory by studying the combined effects of physiological condition and habitat quality on the behaviour of individual mud crabs, Panopeus herbstii , across the spawning season (early spawning season and 2 months after). We assessed the boldness, energy stores and reproductive effort of crabs collected across 10 oyster reefs of low and high quality using laboratory observations and subsequent dissections. Crab boldness was significantly dependent on the interaction between habitat quality and season. While crab behaviour remained relatively constant on healthy reefs, crabs on degraded reefs exhibited a nearly two-fold increase in boldness during the late spawning season, approximating the boldness of crabs on healthy reefs. This behavioural change corresponds to a seasonal shift in crab energy store content and is likely to represent a switch in the primary driving force of crab behaviour. During the early season, crab boldness was positively correlated with short-term stores, whereas later in the season, crab boldness was negatively correlated with long-term stores. Our results suggest that behaviour is driven by predation pressure and refuge availability during the early spawning season, but afterwards depends on replenishing energy stores used for reproduction. These findings support ecological theory and also provide new insight into the stability of behavioural drivers. [ABSTRACT FROM AUTHOR]

Motion vision originated during the Cambrian explosion more than 500 million years ago, likely triggered by the race for earliest detection between preys and predators. To successfully evade a predator's attack a prey must react quickly and reliably, which imposes a common constrain to the implementation of escape responses among different species. Thus, neural circuits subserving fast escape responses are usually straightforward and contain giant neurons. This review summarizes knowledge about a small group of motion-sensitive giant neurons thought to be central in guiding the escape performance of crabs to visual stimuli. The flexibility of the escape behavior contrasts with the stiffness of the optomotor response, indicating a task-dependent early segregation of visual pathways. [ABSTRACT FROM AUTHOR]

Physical traits such as body size and weapon size typically reflect an individual's resource holding potential (RHP). During male-male contests, contestants use these traits to assess their own and their opponent's RHP. However, the advertisement of RHP does not always predict contest outcome. Here, we examined whether assessment index (body size or weapon size [major cheliped size]) and assessment tactics (self or mutual) are predictors of outcome in male-male contests of the hermit crab Pagurus minutus. In experimental contests over guarded females, intruders did not escalate the contest when their major cheliped was smaller than their opponent's, implying that intruders use mutual assessment based on weapon size when deciding whether to escalate a contest. After escalation, intruders succeeded in taking over females within a shorter period of time with increasing major cheliped size relative to their opponent's. Overall, males with a major cheliped that was larger than their opponent's were more likely to win the contest, although some intruders later stopped guarding the female they had taken over. The importance of relative weapon size after escalation indicates that mutual assessment was also used in this phase of male-male contests. Together, these results suggest that males of P. minutus use mutual assessment based on weapon size throughout male-male contests, and that weapon size is an honest index of RHP. Significance statement: We examined whether assessment index (body or weapon size) and tactics (self or mutual) are predictors of outcome in male-male contests of the hermit crab Pagurus minutus. Intruders did not escalate contests when their major cheliped was smaller than their opponent's, implying that mutual assessment based on weapon size was used to decide whether to escalate contests. After escalation, intruders succeeded in taking over females within a shorter period of time and were more likely to win with increasing weapon size relative to their opponent's. The importance of relative weapon size after escalation indicated that mutual assessment was also used in this phase of contests. Together, these results suggest that males of P. minutus use mutual assessment based on weapon size throughout male-male contests, and that weapon size is an honest index of actual strength. [ABSTRACT FROM AUTHOR]

Climate-mediated range shifts into eco-evolutionary novel habitats have the potential to alter the ecology and behaviour of range-expanding species. Of particular concern are behaviours that have a strong impact on the ecology and life history of expanding species. Behaviours that control the spatial patterns of habitat use may be particularly important. We examined site fidelity and foraging foray behaviour of the mangrove tree crab, Aratus pisonii , in its historic mangrove habitat and the recently colonized eco-evolutionary novel salt marsh. In the mangrove, A. pisonii showed both strong site fidelity to individual trees and a foraging pattern wherein they made foraging forays that decreased in frequency as their distance from the home tree increased; but they displayed neither behaviour in the salt marsh. Chemical cues from faeces appear to be the mechanism behind site fidelity in the mangrove and may suggest the mechanism for the loss of this behaviour in the salt marsh where substrate is regularly submerged, potentially preventing establishment of such cues. The loss of site fidelity may affect the foraging behaviour and predation risk of A. pisonii in the salt marsh, leading to a shift in its ecology and bioenergetics. As more species are forced to shift ranges into eco-evolutionary novel habitats, it is important to understand how this shift may affect their life history, behaviour and ecology in indirect ways. [ABSTRACT FROM AUTHOR]

The interplay between a receiver's sensory system and a sender's courtship signals is fundamental to the operation of sexual selection. Male courtship signals that match a female receiver's preexisting perceptual biases can be favored yet the message they communicate is not always clear. Do they simply beacon the male's location or also indicate his quality? We explored this question in a species of fiddler crab Uca terpsichores that courts under elevated predation risk and that mates and breeds underground in the safety of males' burrows. Sexually receptive females leave their own burrows and are thereby exposed to avian predators as they sequentially approach several courting males before they choose one. Males court by waving their single greatly enlarge claw and sometimes by building a sand hood next to their burrow entrance. Hoods are attractive because they elicit a risk-reducing orientation behavior in females, and it has been suggested that claw waving may also serve primarily to orient the female to the male. If the wave communicates male quality, then females should discriminate mates on the basis of variation in elements of the wave, as has been shown for other fiddler crabs. Alternatively, variation in elements of the claw waving display may have little effect on the display's utility as a beacon of the location of the male and his burrow. We filmed courting males and females under natural conditions as females responded to claw waving and chose mates. Analysis of the fine-scale courtship elements between the males that females rejected and those they chose revealed no differences. When predation risk during courtship is high, males' courtship displays may serve primarily to guide females to safe mating and breeding sites and not as indicators of male quality apart from their roles as beacons. [ABSTRACT FROM AUTHOR]

Mussel losses peak after relaying seed on culture plots. The present paper is an attempt to examine the role of shore crab predation and initial mussel density on mussel losses in mussel bottom culture using an intertidal culture plot as a case study. Because of their small size and loose attachment, mussels are particularly vulnerable to predation at this stage, as well as to handling stress and intraspecific competition. In the experimental field plots (1 × 1 m) in the intertidal Oosterschelde, three different densities (1, 5 and 10 kg m) of mussel seed are laid, with half of the experimental plots protected from predation by means of exclosures. Duration of the experiment was 5 weeks (August-September 2012) post-seeding. Protection was the major factor accounting for biomass production, followed by mussel density. Loss rates increased with mussel density, both in the exclosures and in the exposed plots. Losses in the exclosures with the lowest density were still 45 %. There are indications that handling stress prior to the start of the experiment played a major role in these losses. At the higher densities in the exclosures, losses increased to 72.1 % and were not significantly different between 5 and 10 kg m. About one-third of the total loss (32.6 %) was attributed to shore crab predation. The number of shore crabs observed on the plots did not differ between treatments. Byssal thread development during the experimental period was followed and was found to be a slow process that was insufficient to protect mussels from crab predation at the sheltered experimental location. [ABSTRACT FROM AUTHOR]

Prey responses to predator cues are graded in intensity in accordance with the degree of threat presented by the predator. In systems in which prey gather information on predators by using chemicals, prey often respond more to the odor of predators that have consumed conspecifics, as opposed to heterospecifics. We investigated the response of a prey species, the mud crab, Panopeus herbstii, to urine of blue crab, Callinectes sapidus, fed mud crabs or oysters. Behavioral analysis was combined with metabolomics to characterize bioactive deterrents in the urine of predators fed different diets. Urine from blue crabs fed oysters or mud crabs depressed mud crab foraging when presented singly, with the urine derived from a mud crab diet being more potent. The magnitude of foraging depression increased with urine concentration. When urine from blue crabs fed oysters or mud crabs was combined, response to the urine mixture was no different from that to urine derived only from a mud crab diet. Metabolomics analysis indicated diet-dependent differences were related to a set of shared spectral features that differed in concentration in the respective urines, likely consisting of aromatic compounds, amino acids, and lipids. Taken together, these results suggest mud crabs distinguish diet of, and therefore the risk imposed by, predators through detection of a suite of compounds that together represent what the predator has recently consumed. [ABSTRACT FROM AUTHOR]

Larval development in brachyuran crabs includes a number of zoeal stages followed by a single megalopal stage. Zoeae and megalopae are relatively strong swimmers, and movement up or down in the water column takes advantage of vertical shear in ambient currents with consequent transport in the horizontal dimension. For some species, this process is important in controlling the dispersal of early-stage larvae away from spawning sites and in maintaining the supply of late-stage larvae to juvenile nursery habitat. For other species it enables retention near spawning sites throughout the larval period. Vertical position in the water column also modulates predator-prey interactions, which impact growth and survival of larvae. Swimming behavior in larval crabs is regulated by both external cues detected in the water column and endogenous rhythms entrained by external oscillators. Gravity, hydrostatic pressure, and light are the primary external cues because of their predictability in the environment. Light is also the most common external oscillator entraining swimming rhythms. Secondary cues include salinity, temperature, turbulent kinetic energy, and feeding state. Crab larvae also respond to chemical and tactile cues that facilitate settlement in juvenile habitat. This paper presents a review of the physical and chemical characteristics of these cues, the behavioral responses of crab larvae to the cues, and the patterns of larval transport that emanate from these responses. [ABSTRACT FROM AUTHOR]

Dominance and the establishment of social hierarchies are frequently related to size: the larger individuals gain greater reproductive success, while the smaller ones display alternative mating strategies. We studied the existence of dominance and the alternative mating strategies among Neohelice granulata small (SM) and large (LM) males competing for burrows. LM construct burrows with copulation chambers while SM do not. Field studies showed the existence of a SM's size-range of 30-32 mm carapace width when they change behavior and occupy burrows with copulation chambers (hereafter referred to as the 'switch size-range'). We found a restricted size-range in mating pair formation. Laboratory experiments showed that LM dominate SM because SM did not construct burrows in the presence of LM, and LM displaced SM from their burrows. When given the chance, recently mated SM occupied burrows without copulation chambers while not recently mated SM occupied chambered burrows. This is evidence that these males may be displaying a cheating mating strategy to copulate with females looking for these burrows: they occupy but do not own these burrows. SM can also intercept and mate females on the surface. Given the size restriction in pair formation, intermediate-sized males in the switch size-range (30-32 mm carapace width) may copulate with a broader female size-range, larger and smaller than themselves. In this way, SM in the switch size-range may be acquiring a higher reproductive success by adopting multiple tactics. Male dominance hierarchies have been well documented in crustaceans, except for crabs. Here, we demonstrate male dominance related to the construction and defense of burrows and male size in the crab N. granulata. We found that small males of a certain size range adopt an alternative 'cheating' mating strategy that can enhance fitness. Therefore, although they are not large and dominant, small males can nevertheless achieve high reproductive success as a result of this alternative reproductive tactic. [ABSTRACT FROM AUTHOR]

The article discusses the prevalence of the misinformation on fiddler crab claw reversal. Listed are websites mentioning topics regarding fiddler crabs, including Darwin's Finch, Wild informatics and Dreamfish.com. Noted are studies conducted by several researchers on the reversal of fiddler crab claw which include Young and colleagues in 1994, Norman and Jones in 1991 and Simonson in 1985.

The article focuses on the behavior and life of the male yeti crab on the East Scotia Ridge, Southern Ocean. Topics discussed include an overview of the male yeti crab, the low number of this species, their behavior, their higher growth rate in the chimney system's warmer waters, and their space limitation.