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• 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]

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]

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]

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]

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]

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]

The air exposure behavior of the semi-terrestrial crab Neohelice granulata during severe hypoxia was studied. This study also verified whether this behavior mitigates possible oxidative damage, namely lipoperoxidation, caused by hypoxia and reoxygenation cycles. The lethal time for 50% of the crabs subjected to severe hypoxia (0.5 mgO 2 ·L − 1 ) with free access to air was compared to that of crabs subjected to severe hypoxia without access to air. Crabs were placed in aquaria divided into three zones: water (when the animal was fully submersed), land (when the animal was completely emerged) and intermediate (when the animal was in contact with both environments) zones. Then the crabs were held in this condition for 270 min, and the time spent in each zone was recorded. Lipid peroxidation (LPO) damage to the walking leg muscles was determined for the following four experimental conditions: a—normoxic water with free access to air; b—hypoxic water without access to air; c—hypoxic water followed by normoxic water without air access; and d—hypoxic water with free access to air. When exposed to hypoxic water, N. granulata spent significantly more time on land, 135.3 ± 17.7 min, whereas control animals (exposed to normoxic water) spent more time submerged, 187.4 ± 20.2 min. By this behavior, N. granulata was able to maintain a 100% survival rate when exposed to severe hypoxia. However, N. granulata must still return to water after periods of air exposure (~ 14 min), causing a sequence of hypoxia/reoxygenation events. Despite increasing the survival rate, hypoxia with air access does not decrease the lipid peroxidation damage caused by the hypoxia and reoxygenation cycle experienced by these crabs. [ABSTRACT FROM AUTHOR]

Abstract: Information about the roles of both sexes in pair formation is required to better understand the mechanisms involved in sexual selection. Mate choice could depend on the courtship behavior, involving chemical, tactile and visual signals. We determined if Neohelice granulata mate choice is based on female or male choice, considering visual and chemical with contact and without contact signals between partners and different categories of individuals: receptive and unreceptive females; and large, small, mated or unmated males. Experiments showed that mate selection was based on receptive female's choice using chemical signals, but not visual ones. Since copulation occurs during high and low tides, water-borne chemical signals would be preferentially used during high tide, while contact ones during low tide. Females preferred large and unmated males, while males did not seem to recognize receptive females using chemical neither visual signals. Females were capable of detecting the presence of the chemical signals released by large and unmated males, but not its amount. It is proposed that small and mated males are probably releasing different types of chemical signals, not attractive to females, or that they are not emitting any signal. [Copyright &y& Elsevier]

Along its range of distribution, Lithodes santolla can be fished at sites with wide ranges of temperature (5°C to 12°C), suggesting a wider temperature tolerance than is observed for other members of the Lithodidae family. The present study aimed to evaluate the thermoregulatory behaviour of juveniles of L. santolla of different ages, maintained in laboratory conditions at 12°C for 390days and based on: i) temperature selected along a thermal gradient and ii) thermal window calculated as the tolerance temperature interval. Results demonstrate that age is a key factor to be considered in thermal tolerance studies, because the thermal tolerance can change, depending on the age and life cycle stages. The preferred temperature was 12°C for animals aged between 45d and 170d and was 7.2°C and 9.1°C for crabs aged between 260 and 390d, respectively. The critical thermal minimum (CTMin) significantly changed together with the age of crab; the highest value (4.2°C) was for animals 260d old and lowest for crabs 45d old (1.5°C). Critical thermal maximum values were also affected by age, with highest values for animals aged between 105d and 170d (27°C to 27.6°C). The temperature tolerance interval fluctuated between 20.5°C and 25.5°C. Crabs aged between 45d and 260d showed the narrowest interval (22.9°C and 20.5°C, respectively). Considering the thermal limits observed in the present study, a climate change scenario with an increasing frequency and intensity of extreme thermal events might affect the present distribution of the species. Temperature rises would allow L. santolla to explore higher latitudes, whereas a temperature decrease when juveniles are searching for a particular colder habitat, near to CTMin, might be detrimental to the population. [ABSTRACT FROM AUTHOR]

Abstract: The deep-water red crab Chaceon affinis is the largest species of the family Geryonidae. Unlike other species of the same genus, C. affinis is not yet subject to intense commercial exploitation but it has been appointed as a new target resource in European waters, in spite of the lack of information on its biology, life cycle and distribution, which is essential to provide advice for a sustainable exploitation. Here we report for the first time the presence of C. affinis in the Gorringe Bank and give the first account of the mating behavior of this species. All mating pairs were found at the interface of the Mediterranean Outflow Water with North Atlantic Deep Water, suggesting that environmental parameters associated with the interface of these water masses may be relevant for mating in this species. The majority of C. affinis was mating which is an indication of synchrony and reproductive seasonality. A biennial female reproductive cycle is hypothesized, involving molting and mating in the first year with subsequent oviposition during the autumn, and spawning during spring of the second year. We suggest that synchrony and seasonality in the reproduction of C. affinis is linked to the formation of phytoplankton blooms in surface waters, with females carrying embryos from autumn to spring, possibly timing the release of planktotrophic larvae to exploit a seasonal peak in surface productivity and its export. [Copyright &y& Elsevier]

Abstract: Although large crabs are recognized as important sediment disturbers influencing the structure of benthic communities, the role of dominant predatory crabs in soft-bottom habitats along the Humboldt Current Ecosystem, remains largely unknown. A field study was conducted, hypothesizing that the digging activity of these predators disturbs the habitat thereby leading to a reduction in individual abundance, biomass and species richness; these changes result in a modified structure of macrobenthic communities. A directed sampling (crab pits vs. reference areas) showed significant reductions in total abundances in pits compared to reference areas, but no differences were observed in taxonomic richness or benthic biomass. Short-term cage experiment showed significant decreases in total abundance and biomass of macroinvertebrates in predator inclusion treatments compared to exclusions and controls. In consequence, our results confirmed that burrowing activities and the generation of small disturbed sediment patches influence the community structure. These results highlight the importance of large cancrid crabs in soft-bottom habitats, where their modification of the physical configuration of the sediment affects community structure over small spatial scales. Crabs are thus an important source of spatial heterogeneity of the sea-floor landscape. This ecological role must be considered in management strategies of the extensive artisanal fishery for these crabs, as current evidence is showing increasing populations of intermediate predators (like cancrid crabs) in many benthic habitats in response to the depletion of top predators. [Copyright &y& Elsevier]

Abstract: Competent larvae of most benthic marine invertebrates including brachyuran decapod crustaceans can delay their settlement and metamorphosis in the absence of suitable environmental cues. This however may carry significant costs for the post-larval performance and fitness of early benthic juveniles. In this paper, we examined in the laboratory whether delayed larval metamorphosis affects early juvenile performance of the mangrove crab Ucides cordatus, measured as survival and growth through the first five juvenile crab stages (JI–JV). We further investigated whether ‘carry-over’ effects of an extended larval period vary intraspecifically among juveniles from three different hatches (F1–F3). Ucides megalopae were cultivated in two treatments. In the first one, the control, megalopae were cultivated continuously in exposure to conspecific crab odours (adult-conditioned seawater=ACSW) until moulting to the first juvenile crab stage. In the second, the delay-treatment, settlement-competent megalopae were kept for 20days in pure filtered seawater without metamorphosis-triggering odours. From day 21 onwards, megalopae were transferred to ACSW to induce larval moult. The results showed that delayed metamorphosis affects early juvenile survival and growth of U. cordatus. In the delay-treatment, survival rates of juveniles (JI–JV) from F1–F3 were 11–31% lower and intermoult development periods 1.5–4.2days longer than in the control. Delayed juveniles (F1–F3) exhibited 9.2–14.1% smaller body sizes (carapace width) and 1.4–3.9% lower growth rates mostly in the first two moulting events compared to specimens derived from non-delayed megalopae. Most of the detrimental effects were observed in almost all five crab stages studied, indicating that the costs of delayed metamorphosis may persist throughout early juvenile development. Juvenile morphology, however, was not affected. Our study also showed that carry-over effects of delayed larval moult vary intraspecifically among offspring produced by different females. This plasticity in phenotypic effects could relate to differences in the nutritional state, health or age of the females, to stressful environments during embryogenesis or to genetic differences. The observed carry-over effects of delayed settlement on early juvenile performance may affect the overall recruitment success and population dynamics of U. cordatus. In the field, such a situation would appear when new mangrove areas void of conspecific crabs are colonized or when degraded sites are re-populated by larvae originating from elsewhere populations. [Copyright &y& Elsevier]

Abstract: Many crab fisheries target large males, which can cause their densities to differ greatly in areas where they are fished and areas where they are protected, such as inside marine reserves. The size and gender of crabs potentially affect their ability to compete for resources, with competition likely to favour larger male crabs, raising the potential for cascading effects on females or smaller crabs in reserves. The role of size and gender in structuring the outcomes of competitive interference interactions between mud crabs (Scylla serrata Forskal) was tested by placing crabs in tanks with a competitor of smaller, equal or greater size, and of the same or differing gender. The behaviour of crabs was recorded for 15min, and the times spent feeding, attacking, threatening and avoiding were compared among the different size and gender combinations. Male and female crabs spent less time feeding and more time avoiding in the presence of larger male than larger female crabs. Female crabs spent more time avoiding male crabs of equal size than female crabs of equal size. Male crabs of equal size spent the most time attacking. The size and gender-dependent responses of mud crabs to competition may lead to quite unexpected effects inside marine reserves. [Copyright &y& Elsevier]

Abstract: Predation and adaptations to avoid predation during early life stages have great potential to structure population dynamics and resultant community structure. Crypsis is the primary predator-avoidance mechanism for recently-settled red king crabs (Paralithodes camtschaticus); however, it is unknown if this behavioral adaptation is innate or gained with experience. Hatchery-cultured individuals may be at a disadvantage once released into the wild if they have no experience with predators. We conducted experiments with Pacific halibut (Hippoglossus stenolepis) and Pacific cod (Gadus macrocephalus) predators to determine if red king crab predator responses could be enhanced with experience. We exposed crabs to predators for 48h either with limited exposure (chemical and visual cues only) or complete exposure (chemical, visual, and physical cues) and used video recordings to compare (1) crab crypsis, (2) crab survival, and (3) predator behavior (attack rates, capture success) among naïve and experienced crabs. Halibut and cod exposure enhanced crab crypsis and survival, but only halibut exposure resulted in a significant effect. Crabs with limited and complete halibut exposure had higher initial crypsis, and both naïve and conditioned crabs increased crypsis by the end of the experiment. Complete exposure initiated a stronger response compared to limited exposure. Physical interactions with predators are likely important to initiate enhanced avoidance responses. Halibut and cod attack rates and capture success did not vary when crabs had prior experience, but halibut were generally more successful at capturing prey than cod. Our results show that juvenile red king crabs respond to some predators by increasing their cryptic behavior and that this response may be enhanced with experience. For stock enhancement programs, exposing juveniles to predators in the hatchery prior to release may enhance predator avoidance and allow quick adaptation to the natural environment. [Copyright &y& Elsevier]

Abstract: In organisms using a wide variety of refuges, both the cost and benefits to the users might be refuge-specific. Under these circumstances, users using mechanisms (e.g., behavioral preference) that allow them to find and colonize refuges in which net benefits are maximized are expected to be selected by the environment. Herein, we tested the hypothesis that resource generalists display strong preferences for resources that provide the greatest reproductive benefits using Calyptraeotheres garthi, a crab that inhabits the limpets Crepidula cachimilla and Bostrycapulus odites in the south-western Atlantic. In the field, female crabs inhabiting C. cachimilla featured larger average body size, and subsequently, larger average fecundity and brood weight than those inhabiting B. odites. Thus, C. cachimilla is a higher quality host for C. garthi compared to B. odites. In contrast to expectations, host selection experiments revealed that female crabs were attracted to the host species from which they were collected and not to the host species that provided the greatest reproductive benefits (C. cachimilla). Host chemical and/or visual cues imprinted in crabs early during ontogeny (soon after colonization of their first host), rather than genetic differences, may explain the source-host fidelity of C. garthi. In the two hosts, females of C. garthi lead a solitary lifestyle and appear to inhabit the same host individual for long periods of time as indicated by the close relationship between female crab and host body size. The frequency of male–female pairs within host individuals was lower than expected by chance alone. Also, males were, on average, smaller than females and did not appear to inhabit the same host individual for long periods of time. The above suggests that males might be using a pure‐search mating strategy, continuously roaming among host individuals in search of receptive females. The details of the mating system of C. garthi need to be further investigated. [Copyright &y& Elsevier]

Abstract: Understanding the invasibility of marine species with complex life cycles requires examination of the ecology of both larval and adult stages. The goal of our study was to determine whether several species of coastal fish native to the western North Atlantic Ocean can consume megalopae of the nonindigenous Asian shore crab Hemigrapsus sanguineus and, if so, whether megalopae can respond to chemicals from potential fish predators by either molting faster to a benthic crab stage or exhibiting avoidance behaviors. Laboratory predation experiments showed that all fish species tested (cunner, Tautogolabrus adspersus; tautog, Tautoga onitis; grubby, Myoxocephalus aeneus; scup, Stenotomus chrysops; and mummichog, Fundulus heteroclitus) consumed H. sanguineus megalopae. When megalopae were reared in seawater in which fish or adult crabs had been housed, fish chemical cues had no effect on molting rate whereas chemicals from adult conspecific crabs accelerated molting. Behavioral responses of H. sanguineus megalopae to chemicals from fish and crabs were tested in still and flowing water. In still water, megalopae moved away from chemicals from T. adspersus and M. aeneus. In flowing water, chemicals from T. onitis caused a behavioral reaction that led to enhanced movement away from the source of the cue. All 3 species are related to fishes present in the native range of H. sanguineus. In contrast, chemicals from adult crabs and F. heteroclitus had no effect on behavior of megalopae. Behavioral responses of H. sanguineus megalopae to chemical cues from coastal fish species might function as antipredator strategies that enhance survival of this nonindigenous species. [Copyright &y& Elsevier]

A major challenge in neurobiology is to understand how brains function in animals behaving in the complexity of their natural environment. Progress will depend on our ability to correctly interpret results from laboratory experiments in the light of information processing demands identified by studying the organization of behaviour and the flow of information in naturally behaving animals. Predator avoidance responses of semi-terrestrial crabs offer an excellent opportunity for such an approach. We review here findings from two distinct lines of research: (1) Field studies which have characterized the structure and context of escape behaviour to real and dummy predators, and (2) Laboratory studies which have used computer-simulated images and in vivo intracellular recordings to identify and characterize individual neurons implicated in the control of escape. The results of both approaches highlight the influence of behavioural and environmental context in structuring escape. In order to understand how context and the complex flow of signals are processed and translated into behaviour in natural environments it is imperative that future studies take electrophysiology outdoors. [Copyright &y& Elsevier]

Abstract: Marine snails have two predator avoidance strategies: withdrawing into the refuge of their shells and fleeing by crawling away. Here we exposed the marine snail, Nucella ostrina, to water-borne cues from injured prey and a common predatory crab, singly and in combination. We determined whether snails avoided cues from the different cue sources and quantified how long snails spent in passive avoidance (i.e., withdrawn in the shell) before switching to active avoidance behavior (i.e., crawling away) under different cue combinations. Active avoidance behavior was induced by all cue treatments, but the proportion of snails exhibiting passive avoidance and the time taken to switch from passive to active avoidance depended on cue combination. Cues from injured prey induced rapid initiation of active avoidance and little passive avoidance, while cues from crabs alone increased the incidence of passive avoidance and increased time spent withdrawn in the shell; suggesting that alarm cues from injured prey and predator cues elicit opposite behavioral strategies in N. ostrina. The combination of cues from injured prey and crabs induced an intermediate response; snails remained in their shells longer than those exposed to injured prey alone and initiated crawl-away behavior sooner than those exposed to crabs alone. These results suggest that different risk cues interact additively in providing risk information for N. ostrina. Future studies of antipredator behavior in marine snails should consider the possibility that different types of risk cues may induce different types of avoidance behavior. [Copyright &y& Elsevier]

Abstract: Bright colours are a key visual signal in many animal communication systems. Here we examine the function of the blue-green facial bands found in two species of mangrove crabs, Perisesarma eumolpe (De Man) and P. indiarum (Tweedie). Food (mangrove leaves) deprivation and re-feeding experiments demonstrated that facial band brightness and saturation changed significantly with nutritional status. These results suggest that the colours are diet-derived and could be carotenoid-based. Manipulation of the facial bands had significant effects on inter-crab behaviour. When P. indiarum and P. eumolpe males were given a choice between a female with its facial band blacked out and a similar-sized control female with natural colour, they consistently chose the latter. In a resource holding potential (RHP) experiment, male crabs defending burrows responded differently to male con-specific intruders with blacked out facial bands compared to non-blacked out controls. Together, the results show that brightly coloured facial bands in P. eumolpe and P. indiarum are important for communication; either as a way to identify conspecifics, or to convey nutritional status and hence physical quality. [Copyright &y& Elsevier]

Abstract: The antimicrobial peptide scygonadin (Scy) was first isolated from the gonad of Scylla serrata and its gene is predominantly expressed in the ejaculatory duct of adult males. Thus, its function was predicted to be associated with reproductive immunity, but this is still unclear and needs further investigation. In our study, the expression pattern of Scy at different developmental stages of both male and female S. paramamosain was investigated, so that the potential function of this peptide could be examined. Using real-time quantitative PCR, Scy mRNA transcripts were demonstrated obviously in the vulnerable embryos and larvae-zoea I but very weakly detected in the larvae-zoea III, megalops and juveniles. The gene expression pattern showed a decreasing trend during the early developmental stages. The Scy gene had low expression in the ejaculatory duct of small and medium crabs (100g and 200g in weight) whose gonads were underdeveloped. However, the level of Scy expression was significantly increased in large crabs (300g in weight), which had normally become sexually mature at this size. It was further observed that the numbers of Scy mRNA transcripts in sexually mature crabs were significantly more abundant than in immature ones. In addition, the Scy gene was significantly expressed in the ejaculatory duct of mature male crabs during the mating period (April and May) and reached their highest expression in May. Using immunohistochemistry, the Scy protein was strongly detected in the testis and seminal vesicle of small crabs. However, in large crabs, Scy protein was intensively present in more tissues than in small crabs, including the ejaculatory duct, posterior ejaculatory duct, gill and muscle of males, and also in the spermatheca, gill and muscle of females. It is also interesting to note that Scy mRNA transcripts were detected in other crab species and showed similar expression pattern to those in S. paramamosain. This study extended our knowledge concerning the antimicrobial peptide scygonadin, which has its function principally in the ejaculatory duct of males but which may also play a role at different developmental stages of S. paramamosain from embryogenesis to maturation, and is also widely distributed in other crabs. [Copyright &y& Elsevier]

Abstract: Estuaries represent highly dynamic environments, especially with respect to salinity. Exploitation of these habitats by marine species can assist their ecological success, however they require specialized behavioral strategies as well as physiological abilities to cope with the fluctuations of physical stressors. The Valdivia River estuary, southern Chile, is a site of high larval recruitment and juvenile abundance of the commercial crab species Cancer edwardsii, particularly during the spring and summer months. This estuary experiences severe low salinity events (<7.5) for periods exceeding 6h, that are associated with rainfall events and the subsequent higher flow rates of the tributaries. To determine the strategies employed by juvenile crabs living in the inner portions of the estuary in the face of changes in salinity conditions, we evaluated their survival and behavioral responses when exposed to a salinity gradient. Early juveniles were incubated at salinities of 0, 7.5, 15–22.5, 32 and crab mortality was recorded after 1, 6 and 12h of exposure. In addition, early juveniles were experimentally exposed to continuous and gradual changes in saline conditions to evaluate their behavior, which was recorded on video. The main results were (1) despite most Cancer species being considered weak osmoregulators, 30% of individuals of C. edwardsii were able to survive freshwater conditions for 12h. (2) burying and not quiescence behavior was associated with a drop in salinity, (3) in severe hyposaline conditions, the crabs increased their survival burying in the substrate, probably using higher salinity (>22) interstitial water. Our findings suggest that burying behavior plays a key role in allowing the crabs inhabit inner estuarine areas where sudden and unexpected severe hyposalinity events occur. [Copyright &y& Elsevier]

Abstract: Adult green crabs are highly aggressive predators that exhibit fast population growth in newly invaded areas and potentially compete with juvenile lobsters for limited resources. Previous studies suggest that juvenile lobsters utilize shelter to avoid predation but shelter dependence decreases as they mature and develop predator defense mechanisms. Smaller lobsters must therefore trade-off energetic needs with predation risk. In laboratory experiments we examined how the presence of an adult green crab affects foraging and shelter behavior of juvenile lobsters (25–51mm CL) by offering juvenile lobsters protective shelter and an adjacent food patch in the presence or absence of a green crab. For each trial we monitored lobster behavior over 8h. Our results indicate that in the presence of a green crab, small juvenile lobsters (<35mm CL) spent significantly less time foraging and more time within the shelter. These small juveniles also spent significantly less time feeding and/or handling the food but took longer to actually locate the food source. In contrast, the presence or absence of a green crab did not have any influence on the results of trials that used juvenile lobsters over 35mm CL. Thus, green crabs can significantly influence foraging and shelter usage of small (<35mm CL) juvenile lobsters and re-affirm the idea that this early stage represents the most vulnerable in the benthic life cycle of lobsters. [Copyright &y& Elsevier]

Abstract: Monitoring effects of contaminants at lower levels of biological organisation (e.g. biochemical and cellular) allows for mechanistic evaluation of effects of contaminant exposure through laboratory exposures. However, higher level organism effects (e.g. physiological and behavioural) are deemed more ecologically-relevant. In the present study, cellular (cell viability and immune function), physiological (cardiac activity) and behavioural (foraging behaviour) responses were evaluated in field-collected shore crabs Carcinus maenas from three estuaries [a ‘relatively’ (polycyclic aromatic hydrocarbon) PAH-contaminated site (Plym Estuary) and two ‘comparatively clean’ field sites (Avon and Yealm Estuaries)] and compared with responses of crabs exposed in the laboratory to a model organic contaminant (PAH) pyrene (200 μg l−1 for 28 days). The hypothesis that behavioural indicators may be more sensitive than other more traditional methods was tested. No significant impacts were observed at the cellular or physiological level in Plym-collected crabs (the ‘relatively’ contaminated site), but foraging behaviour was significantly altered (increased prey handling time) compared to individuals collected from the ‘relatively’ uncontaminated sites (Avon and Yealm). When given a cockle as a prey item, both Plym-collected and laboratory-exposed crabs took longer to handle and break into cockle shells. Therefore, ecologically-relevant behavioural observations may serve as valuableindicators of environmental quality. [ABSTRACT FROM AUTHOR]

Abstract: In a previous work we found that size-matched Chasmagnathus crabs establish winner–loser relationships that were stable over successive encounters but no evidence of escalation was revealed through fights. Here, we evaluated the hypothesis that size-matched fights between these crabs would be resolved according to the contestants'' level of aggressiveness. Moreover, we aim at analysing the proximate roots of aggression, addressing the influence of the biogenic amines serotonin (5HT) and octopamine (OA) in crab''s agonistic behaviour. To achieve these purposes, the following experiments were carried out. First, we performed successive fight encounters between the same opponents, varying the number of encounters and the interval between them, to assess the stability and progression of the winner–loser relationship. Then, we analysed dominance relationships in groups of three crabs, evaluating the emergence of linearity. Thirdly, we examined the effects of 5HT and OA injections over the fight dynamics and its result. Our findings show that contest outcome is persistent even through four encounters separated by 24h, but a comparison between encounters does not reveal any saving in fight time or increase in the opponent disparity. Within a group of crabs, a rank-order of dominance is revealed which is reflected in their fight dynamics. Interestingly, these results would not be due to winner or loser effects, suggesting that fight outcome could be mainly explained as resulting from differences in the level of aggressiveness of each opponent. Moreover, this individual aggressiveness can be modulated in opposite directions by the biogenic amines 5HT and OA, being increased by 5HT and decreased by OA. [Copyright &y& Elsevier]

Abstract: Little is known about nursery habitat function for red king crab (Paralithodes camtschaticus), a commercially important species that associates with complex benthic habitats from settlement through the first two years of life. During settlement, the red king crab actively seeks complex benthic habitats, with high availability of vertical structure and crevice space. Habitat choice for early juvenile red king crab may be driven by habitat complexity, or a function of several potential mechanisms, including foraging requirements, and shifting ontogeny. We established habitat preference and foraging behavior for two size classes of age-0 red king crab (small 2–4mm, and large 7.5–9mm carapace length) with laboratory experiments using habitat treatments composed of individual complex substrates that were living, biogenic substrates, including structural invertebrates, bryozoans and hydroids, and macroalgae in branched and blade forms. Non-living structural mimics of the biogenic substrates were presented to crabs as clean and fouled mimic treatments. We quantified the proportion of crab associations and foraging activity with single habitat treatments within a 24h period. Substrates that were statistically attractive to small crabs were paired to test small crab foraging behavior. A variety of substrates were statistically attractive to red king crab. Small crabs associated with complex biogenic habitats and fouled mimics (group mean±SE 64%±4%) more often than clean mimics (29%±4%), and preferred to forage on the structural invertebrates (foraging frequency 81%) when presented with paired biogenic and fouled mimic substrates. Large crabs associated with habitats composed of structural invertebrates (group mean±SE 78%±2%) statistically more often than macroalgae and fouled and clean mimics (32%±5%). Strong attraction to structural invertebrates by early juvenile red king crab is likely driven by foraging opportunities. Our experiments demonstrate that biological habitat features may be functionally more important to early juvenile red king crab than complex physical structure alone. Habitats formed by structural invertebrates, in particular, may enhance growth and survival of early post-settlement stage red king crab in excess of other highly structured habitats, including macroalgae and complex physical substrates. [Copyright &y& Elsevier]

Abstract: The evolutionary history of the Anomura has long been controversially discussed. One aspect that has received little attention is the dissimilarity in physiological tolerances of the related families Paguridae and Lithodidae to environmental conditions, and how this may have determined the divergence and radiation of the families into different distribution ranges, in particular with regard to the limited penetration of the deep sea by the Paguridae. This study investigates the physiological tolerances of the temperate shallow-water hermit crab, Pagurus cuanensis, to various temperature (5, 10, 15, 20°C) and pressure regimes (1 to 100atm) by measuring the standard metabolic rate (SMR) and behavioural changes. SMR was primarily affected by temperature, with a notably low rate at 5°C throughout all pressures. Behaviour was affected by pressure, with an increase in pressure from 50 to 100 atmospheres (atm) resulting in reduced activity. It is suggested that this species can tolerate hydrostatic pressures greater than those found in its natural bathymetric range. It is discussed that a lack of physiological cold tolerance and ecological factors, such as the need to find gastropod shells for protection, are the principal restrictions maintaining P. cuanensis to a maximum depth of approximately 250m. We hypothesize that temperate shallow-water invertebrates could indeed be able to penetrate greater depths as continental shelf waters warm up in the course of global climate change. [Copyright &y& Elsevier]

Abstract: In temperate marine environments, meroplanktonic larvae face seasonal variations in temperature and food availability. In a laboratory study conducted under seasonally varying temperature conditions, we evaluated the nutritional vulnerability in different cohorts (August, September, October, November, December, and January) of first-stage larvae of a porcellanid crab, Petrolisthes laevigatus. Besides continuously fed and starved control groups (FC, SC), the experimental treatments comprised: (1) differential periods of initial starvation and subsequent feeding (point-of-no-return, PNR: minimum time of initial starvation preventing recovery after later feeding); (2) initial feeding and subsequent starvation (point-of-reserve-saturation, PRS: minimum time of initial feeding allowing for food-independent development through the rest of the moulting cycle); (3) limited daily access to prey (feeding pulses, 4 and 6h/day). The development time of FC larvae ranged from 10.6±0.4days (January) to 21.9±2.6days (August), without significant variation in mortality among cohorts. Under continuous absence of food (SC), first-stage larvae never survived to the zoea II. Short-term feeding pulses had significantly different effects on development time of different cohorts, but not on survival. The PNR was lowest in larvae produced near the end of spring (November). However, when the PNR was expressed as a percentage of the development time in FC larvae, no significant differences were found among cohorts (relative PNR: 32.8–42.5%). The relative PRS was reached after 60.6–73.5% of the development time in FC larvae. In spite of strong seasonal (presumably temperature-induced) differences in the absolute PNR and PRS values of different cohorts, the relative values were generally similar. This suggests that successive cohorts of early larvae can develop with similar success, unless severe winter conditions or oceanographic fluctuations cause a significant decline in short-term prey availability or plankton productivity. Due to long development duration at low temperatures, the larvae produced in winter and early spring have greater potential for dispersal, favoring a genetic exchange between distant populations and colonization of new habitats. Summer larvae, by contrast, may be more important for maintaining local populations. An index of nutritional vulnerability (NVI=PRS50/PNR50) is proposed in this paper to compare larvae with differential developmental times. In most larvae studied so far, the NVI is <1, indicating some degree of independence of food. In larvae of P. laevigatus an index >1 reflects a relatively high degree of dependence on planktonic food, especially in winter larvae. [Copyright &y& Elsevier]

Abstract: Multiple prey species may affect consumption by their shared predator in a non-additive fashion which cannot be predicted by summing pairwise predator–prey interactions within food webs. By manipulating prey species richness and identity in experimental mesocosms, we sought to explore the effects of interspecific prey interactions between pinfish Lagodon rhomboides and pigfish Orthopristis chrysoptera, and between blue crabs Callinectes sapidus and common mud crabs Panopeus herbstii on the consumption rates of a shared predator species, gulf toadfish Opsanus beta. We also determined the effects of these interactions on the survivorship of the prey species as mediated by the predator. In both fish and crab prey trials, interspecific interactions between multiple prey increased the overall consumption rate of O. beta, and in each case, one prey species was harmed (decreased survivorship) while the other prey species was not significantly affected by these interactions (all relative to single-prey treatments). In trials run with fish prey, behavioral observations revealed that L. rhomboides aggressively chased O. chrysoptera out of a seagrass refuge and into a surrounding sand matrix where O. beta foraged, thus increasing O. chrysoptera vulnerability to predation. In trials run with crab prey, C. sapidus failed to reduce their activity in the presence of O. beta. In addition, P. herbstii displaced C. sapidus from the seagrass refuge in mixed prey treatments, and so these conspicuous behaviors primarily occurred in the unstructured sand habitat where C. sapidus were more vulnerable to predation. We conclude that multiple prey effects, including those involving risk-enhancing, agonistic interactions between prey, can be important determinants of predator–prey outcomes. This may be especially true when refuge space is limited. [Copyright &y& Elsevier]

Abstract: Red king crab (RKC) (Paralithodes camtschaticus) are generally associated with structurally complex habitats during the first 2years of benthic life. In this first experimental laboratory study with a fish predator, survival of newly settled juvenile RKC was tested in eight different habitat treatments with varying amounts and types of physical structure, open sand, gravel bottom, and habitat islands. Video observations provided insights on habitat-mediated interactions between Pacific halibut predators (Hippoglossus stenolepis) and crab prey. Survival of RKC increased with amount of physical structure and was highest in the most heterogeneous habitat and in habitats characterized by high density patches. Predator activity decreased with increasing amount of structure, and attacks on RKC were correlated with predator activity. Low survival in open sand habitat was associated with both high attack rate and high capture success (captures per attack). Lower levels of capture success did not vary among the habitats containing algae and other complex physical structures, but attack rates declined with increasing amount of structure, and encounter rate (i.e., prey detection and attack) was the primary determinant of mortality. RKC were capable of detecting predators and adjusted their behavior to avoid predation by sheltering in dense microhabitat patches. Successful stock enhancement for greatly reduced populations of RKC in the Gulf of Alaska will depend upon placing seed stock in habitats with abundant protective habitat, and high quality microhabitats may serve as well as continuous cover. [Copyright &y& Elsevier]

Abstract: Hermit crabs with poor fitting shells are chemically attracted to dying gastropods and conspecifics where a shell may become available. For land hermit crabs, the shell cue is a volatile compound found in the haemolymph. Based on this knowledge, we tested the hypothesis that shell investigation behavior in aquatic hermit crabs, the ancestral predecessors of terrestrial hermit crabs, is also triggered by volatile cues. Volatile compounds from haemolymph of Clibanarius vittatus and Pagurus pollicaris and brachyuran decapod crustaceans were purged from a water–haemolymph solution, trapped in seawater and tested for induction of shell investigation behavior with juvenile C. vittatus. Only volatiles from C. vittatus haemolymph stimulated shell investigation. Volatile compounds were isolated from haemolymph by headspace solid-phase microextraction (SPME) and analyzed by coupled gas chromatography–mass spectrometry (GC–MS). Two prominent compounds were identified, 3-decanol, which was unique to C. vittatus haemolymph, and 2-ethyl-1-hexanol, which was present in the haemolymph of all 4 crustacean species. In shell investigation bioassays, 3-decanol from C. vittatus haemolymph stimulated shell investigation behavior, while 2-ethyl-1-hexanol did not. In bioassays with synthetic 1-, 2-, 4-, and 5-decanol, shell investigation behavior was evoked by 1-decanol, 5-decanol and 3-undecanol. There was no response to 2- and 4-decanol. The response of C. vittatus to volatile shell cues supports the hypothesis that volatile cue detection evolved prior to the occupation of terrestrial niches by crustaceans. [Copyright &y& Elsevier]

Abstract: The study aimed at investigating the effects of sewage loadings on the behaviour of two fiddler crabs species maintained in a system of experimental mesocosms, built in a mangrove area in Tanzania and inundated with different seawater/sewage mixtures. Our results show that sewage loads led to a modification of the overall activity budget of the crab community as a result of increased hypertrophic conditions (high COD, increased chlorophyll-a concentrations). During their activity period, crabs inside contaminated mesocosms seemed to satisfy their feeding demand faster than those of the control cells, spending a significant longer time in other activities like courtship and territorial defence. Apart from being a good biological indication of ecosystem eutrophication, such a reduced foraging activity by fiddler crabs also depresses their sediment bioturbation activity, important factor for the health of mangrove systems, suggesting practical implications regarding the efficiency of mangrove-based wetlands for treatment of domestic sewage. [Copyright &y& Elsevier]

Abstract: Behaviour of juvenile mud crabs, Scylla serrata (70–90mm carapace width, CW) were observed in response to odours of moulting and injured conspecifics and food (pilchard) under controlled flow conditions using bioassay technique. This study was undertaken to better understand the role that chemical cues have in mediating the attraction of cannibal crabs to moulting crabs in an aquaculture growout facility and thus aid in more successful production. In response to moult odour juvenile S. serrata spent 5.6±1.9% of the time in locomotion but this did not differ significantly (P >0.05) from that of control odours (seawater, 2.6±1.2%), however a tactile response was observed for moult odour not seen in controls. Juveniles exposed to the odour of injured conspecifics (12.2±2.3% of time in locomotion) and to food (22.7±3.1%) differed significantly from the seawater control (P <0.05). The possibility that the active agent in moult water is relatively dilute was considered, however varying concentrations of food and crushed conspecific odour failed to demonstrate concentration dependant behavioural results. Variation in the form of size (carapace width) and sex was revealed, so too was preliminary evidence of behavioural differences between crab hatchings. For example, larger crabs (around 80mm CW) increased tactile investigation of the odour inlet pipe in response to the crab-based odours of moulting (3.5±1.7% of the time) and injured conspecifics (2.6±1.0%), though response to food remained constant over all sizes (∼10.0% of the time). In another experiment, larger female crabs maintained a high frequency of tactile response to the odour of injured conspecifics. In males, the response was attenuated in larger individuals. Despite no differences being found between moult odour and controls some evidence exists to suggest that a small proportion of crabs were responding to the moult odour and that this still has the potential to cause a dramatic cumulative reduction in growout survival. Variation in size and subsequent behaviour of individuals poses the question of whether behaviour contributes to growth rate and might be a focus of genetic selection for more uniform growth. [Copyright &y& Elsevier]

Abstract: Organisms ranging from paramecia to humans tend to explore places that have been least recently explored, which is referred to as spontaneous alternation. Although organisms rely on different sources of information in alternating between places, the emergent behavioral pattern is likely advantageous during exploration and foraging. Under this rationale, continuous spontaneous alternation performance of the invasive green crab, Carcinus maenas was assessed and compared with the native blue crab, Callinectes sapidus in a plus-maze submerged in seawater. For the first time spontaneous alternation behavior was demonstrated in Crustacea (i.e., C. maenas) and significant interspecific differences in alternation performance were observed between the invasive versus the native species. Carcinus maneas exhibited a pronouncedly higher spontaneous alternation performance than C. sapidus. Carcinus maneas on average alternated at levels higher than chance, which was not the case for C. sapidus. These observations point to an additional behavioral mechanism that might result in the competitive success of green crabs over blue crabs in areas where they co-occur. Most of the subjects exhibited asymptotic alternation performance from the onset; there was no improvement in their performance over the course of the experimental session. This finding implies the innate nature of this behavioral policy. [Copyright &y& Elsevier]

Abstract: This study tested the hypothesis that physiological condition is a key factor in determining the outcome of intraspecific agonistic interactions for food in male shore crabs Carcinus maenas of equal body size. Physiological condition was manipulated by maintaining crabs under different food regimes (using the cockle Cerastoderma edule) in combination with exposure to a sub-lethal concentration (200 µg L−1) of pyrene, a polyaromatic hydrocarbon (PAH). After 14 days, crabs were used in staged agonistic interactions, whereby, an unexposed crab was paired with a pyrene-exposed crab from the same dietary regime, using a whole cockle (C. edule; 0.35±0.05 g wet weight) as the limited resource. Agonistic behaviour was recorded over 15 min, then crabs were separated and their energetic status was assessed based on haemolymph glucose and lactate concentrations. Fully-fed (fed 2 g of food each day) crabs had significantly higher concentrations of circulating glucose and lactate compared to starved (no food) and diet-restricted crabs (fed 1 g of food on alternate days after an initial starvation period of 3 days). In fully-fed crabs, blood glucose concentrations were lower, on average, in individuals exposed to pyrene. Physiological condition had no significant effect on most behavioural measures used to describe the agonistic behaviour in crabs (e.g. number of fights, number of wrestles, fight duration, wrestle duration, contest duration and contest intensity); however, starved pyrene-exposed individuals had significantly higher resource possession (defined as % time in possession of the resource) and significantly decreased inter-bout intervals (defined as time spent away from an opponent after an agonistic encounter) compared with starved unexposed individuals. Results show that a reduced physiological condition (‘lower’ RHP) in starved contaminant-exposed crabs resulted in an unexpected increased competitive ability over starved unexposed individuals. [Copyright &y& Elsevier]

Abstract: Activity patterns, feeding and burrowing behaviour of the economically important semi-terrestrial mangrove crab Ucides cordatus (Ucididae, L. 1763) was studied in a high intertidal Rhizophora mangle forest stand in Bragança, North Brazil. Video observations in the rainy and dry season were conducted over 24 h cycles at different lunar phases to investigate the behaviour of these litter-feeding crabs outside their burrows. During the rainy season, crabs stayed inside their burrows for 79% and 92% of the time during day and night, respectively. Time spent for feeding, burrowing and other activities outside their burrows was significantly longer during the day with 9.9% (night: 1.7%) and at waning and waxing moon with 9% (full and new moon: 0.9%). At neap tides (no tidal inundation) foraging and feeding activities outside burrows were clearly light-dependent, increasing at dawn and decreasing at dusk. Highest activities during daytime relate to the visual localisation of food. During the dry season, crabs spent less time inside burrows at neap tides than during the rainy season (80% and 91%, respectively). However, time spent for feeding activities was similar during both seasons. During almost all observation periods crabs collected leaf litter, but rarely fed on it outside burrows. At neap tides nearly all available litter was collected, suggesting that the U. cordatus population is litter-limited during these times. At spring tides (regular tidal inundation) the surface activity of U. cordatus was tide-dependent. Crabs closed their burrow entrances 2–3 h before flooding and re-emerged as soon as the tide retreated. During the day, burrow maintenance was the second most frequent behaviour after feeding. Agonistic interactions were regularly observed and were mainly related to burrow defence. The mean foraging radius of the crabs was only 19 cm (max: 1 m) underneath high Rhizophora mangle trees where crab densities were high. The results point to a high competition for burrows and show that U. cordatus is territorial. It is concluded that several exogenous factors, in particular light, leaf litter availability, flooding of burrows and the presence of conspecifics are important in controlling the crabs'' activity patterns. [Copyright &y& Elsevier]

Abstract: Trait-mediated indirect interactions (TMIIs) can vary across mosaics of wave exposure due to variation in predator abundance, foraging efficiency, or morphological and behavioral responses to predators. In this study, we compared how whelks, Nucella lapillus, from several wave-exposed and wave-protected populations transmitted TMIIs initiated by waterborne cues from crab predators (Carcinus maenas and Cancer borealis) and a seastar (Asterias rubens). In laboratory experiments, whelks taken from wave-exposed environments consumed fewer mussels (Mytilus edulis) than did whelks from wave-protected populations. Whelks from wave-protected sites reduced foraging when exposed to cues from Cancer, Carcinus, Asterias, or both Carcinus and Asterias, but whelks from wave-exposed sites only responded to Cancer. In predation trials, both crabs readily consumed whelks taken from wave-exposed populations, but only Cancer consumed the whelks from wave-protected populations. Although Carcinus could crush thin-shelled, wave-exposed whelks, in the presence of Asterias these whelks were consumed by “winkling”. The differing responses of wave-exposed and wave-protected whelks may be explained by several factors: 1) the abiotic stress of wave action may generate a persistent reduction in the overall feeding rates of wave-exposed whelks, rendering TMIIs undetectable, 2) some predators may not threaten whelks in wave-exposed environments, and 3) the threat of wave dislodgement may supercede the threat of predators. Thus, the extent to which Nucella transmits TMIIs will likely depend on the wave-exposure history of whelk populations and the initiating top predator species. [Copyright &y& Elsevier]

Abstract: Blue crabs are cannibalistic, and therefore the scent of injured conspecifics represents both a potential food cue, as well as an indicator of predation risk. We examined the response of blue crabs to conspecific odor alone, as well as in mixtures of attractive cues to determine how animals evaluate and respond to this odor. We explicitly manipulated risk-sensitivity based on either animal size (an indicator of susceptibility to predation) or hunger state (susceptibility to starvation) as ways to evaluate theories of risk-allocation, which suggest that decreases in predation risk, or increases in the risk of starvation, ought to result in diminished responses to sensory cues that signal predator presence or activity. Large and small blue crabs were challenged to locate the source of odor plumes consisting of the scent of injured conspecifics (risk cue), attractive food odors (attractive cue), or their mixture (conflicting cue). Neither large nor small blue crabs tracked aversive cues, but large blue crabs consistently tracked conflicting treatments to their source. Responses to conflicting and aversive treatments also involved diminished movement and reduced tracking speed relative to behaviors displayed in attractive plumes. Thus, even cannibalistic crabs seem to respond more prevalently to the apparent predation risk then to food reward, and risk-sensitive behaviors have a likely cost in terms of reduced food intake. Starved animals were more likely than unstarved animals to track conflicting plumes. Both the ontogenic shift and the response of starved animals support the notion that the cost of risk-aversive behaviors results in this strategy being allocated in proportion to the degree of potential risk. Since risk-aversive responses to chemical cues can produce strong effects in communities, the size-dependent nature of these responses in blue crabs may introduce considerable complexity in interactions between blue crabs, their predators, and their prey. [Copyright &y& Elsevier]

Abstract: Understanding the behavioural mechanisms that underlie prey size preference of predators is an essential component of unravelling the processes that govern predator-prey dynamics. In marine systems, despite being able to consume larger and more profitable prey, many molluscivorous predators show a preference for smaller, less profitable prey, most likely to minimize the risk of damaging feeding extremities. Here we assessed the flexibility of this prey size preference. We observed that shore crabs (Carcinus maenas) that were food deprived, and which were offered mussels (Mytilus edulis) of different sizes in dichotomous preference tests, preferred smaller, less profitable mussels. The same result was observed for crabs foraging with a conspecific competitor. Only crabs that were conditioned to feed on the larger, most profitable mussels shifted their prey size preference and ranked the most profitable mussels as highest. Although shore crabs showed flexibility in prey size preference, through which they would be able to cope with environmental variability, our results in general emphasize preference for smaller prey. We discuss the possibility that crabs maximize their long-term feeding rate, in which case it can be optimal to select these smaller mussels. [Copyright &y& Elsevier]

Abstract: The mole crab Emerita talpoida migrates with the tide in the swash zone of sand beaches. A circatidal rhythm in vertical swimming underlies movement, in which mature male crabs show peak swimming activity 1–2 h after the time of high tides at the collection site. In addition, there is a secondary rhythm in activity amplitude, in which crabs are maximally active following low amplitude high tides and minimally active following high amplitude high tides. The present study determined the phase response relationship for entrainment of the circatidal rhythm with mechanical agitation and whether the cycle in activity related to tidal amplitude could be entrained by a cycle in the duration of mechanical agitation at the times of consecutive high tides. After entrainment with mechanical agitation on an orbital shaker, activity of individual crabs was monitored in constant conditions with a video system and quantified as the number of ascents from the sand each 0.5 h. Mechanical agitation at the times of high tide, mid-ebb and low tide reset the timing of the circatidal rhythm according to the timing relationship to high tide. However, mechanical agitation during flood tide had no entrainment effect. In addition, a cycle in duration of mechanical agitation entrained the rhythm in activity amplitude associated with tidal amplitude. Both rhythms and entrainment effectiveness over the tidal cycle may function to reduce the likelihood of stranding above the swash zone. [Copyright &y& Elsevier]

Hydroacoustics was used to study the influence of tides in the main pelagic fauna composition in Bahía Magdalena in the south of Baja California, Mexico (24°50′N, 112°50′W). The target species were the Pacific sardine (Sardinops caeruleus) and the red crab (Pleuroncodes planipes). Measurements of fluorescence, temperature, and salinity were made along a transect 18km long covering three zones inside the bay, around the mouth of the bay (the main entrance), and the continental shelf. The mouth of the bay was the region of highest fluorescence and lowest temperature, this latter caused by upwelling pulses. Results show two locations where most of the fish were observed, inside the bay and at the main entrance. The preferred locations for the red crab were outside the bay and also the main entrance. The fish and the red crab aggregations were observed in the area of the main entrance particularly during low tide at night. Beside fish density distribution, there were two distinct fish shoaling behaviors along the transect: inside the bay, fish where located in large and compact schools, and in the region of the main entrance where they were scattered in large and small shoals. Results are discussed in terms of the adaptative behaviour of fish shoaling, food availability and seasonal abundance of small pelagics in Bahía Magdalena influenced by tides. [Copyright &y& Elsevier]