Crab Body Research Articles

Choosing a bigger opponent: the path to victory and greater gains for the small contestant

Animals often engage in contests over limited resources. The probability of winning a contest is primarily determined by the individual's fighting ability relative to its opponent and the perceived value of the disputed resource. Individuals of the hermit crab Calcinus californiensis frequently fight over gastropod shells. We conducted a free-choice experiment to assess the factors that determine individuals’ choice of opponent, contest initiation, and contest resolution. We placed hermit crabs occupying two shell species into a large container and monitored agonistic interactions between crabs. We assessed the asymmetries in fighting ability based on the differences in body mass between the opponents. The shell species and fit (i.e., shell size relative to crab body size) were used as measures of the objective and subjective resource value, respectively. Motivation influenced contest initiation; the crabs occupying too-tight shells were more likely to initiate a contest than the ones in looser-fitting shells. In most cases, the attackers fought for a shell with a looser fit, even if that meant losing a tighter-fitting shell of the preferred shell species. The fighting success for attackers was positively associated with the number of bouts of rapping and the shell size improvement. However, success was negatively correlated with body size asymmetry; attackers that chose opponents larger than themselves were more likely to evict their opponent than the attackers that chose opponents that were smaller. Experimental designs that allow animals to select their own opponents, rather than assigning specific opponents, can strongly contribute to knowledge of agonistic interactions.Significance statementFighting dynamics are commonly assessed by estimating the influence of the resource-holding potential and resource value in pair-matched opponents. Here, however, we examined the influence of asymmetries in resource-holding potential and the objective and subjective value of gastropod shells on the choice of a contender and contest resolution through a free-choice opponent experiment in hermit crabs. The contest initiation was driven by the motivation to obtain a better gastropod shell species or one with a better size fit—factors which are known to improve individual fitness. Furthermore, fighting success was associated with an individual's persistence in displaying aggressive behaviors and its motivation to obtain a better resource. However, contrary to the predictions of game theoretical models, fighting success was higher when attackers chose opponents larger than themselves. Our results highlight the relevance of assessing fighting under more natural conditions by allowing animals to select their opponents.

Total body burden of neurotoxicant Hg in Chinese mitten crab (Eriocheir sinensis) - Considerations of distribution and human risk assessment

The Chinese mitten crab (Eriocheir sinensis) is considered one of the 100 most invasive alien species in the world. Despite this, its role in ecosystems, among others, in the trophodynamics of pollutants including mercury, is still not fully understood. Becoming an increasingly important and widespread element of the trophic chain in new areas arouses interest from humans as consumers. Hence it is important to determine the level of contaminants (including Hg) in alien species. In the present study, great attention was paid separately to the soft tissues and hard tissues of the exoskeleton, which may play an important role in the detoxification of the crab's body from toxic Hg. The study was conducted on crabs collected in 2011–2021 in the Vistula Lagoon. Concentrations of total mercury and its forms were carried out using a Direct Mercury Analyzer, DMA-80 (Milestone, Italy). The present study showed that mercury accumulation of the crab's body largely occurred through the gills, followed by the oral route. The distribution of Hg in the crab's organs was related to the trophic origin of the mercury, while halide-bound mercury and semilabile forms from the respiration (filtration) process were redistributed into the crab's exoskeleton. Male crabs, compared to females, had a higher Hg burden on internal organs such as their hepatopancreas and gonads. Hg concentration in hard tissues was closely related to the type of mineralization of the carapace. The elimination of Hg from the muscles and from the hepatopancreas into the carapace was one of the important detoxification processes of the crab's body. Thus, moulting crabs effectively remove Hg protecting its body from the neurotoxin. As a result, a smaller Hg load is biomagnified, making the crab's muscle tissue fit for human consumption. The observed decrease in Hg concentrations from 2011 to 2021, as well as the spatial variability of Hg in the crab's muscles, testify that the crab can serve as a biomonitor for ecosystem changes.

Water temperature and season length interact to explain a rare non‐linear ecogeographic cline in body size

AbstractAimAdult body size often exhibits patterns across large‐scale environmental gradients, creating ecogeographic clines. However, the form of body size clines varies across taxonomic groups, with linear and non‐linear patterns in body size observed in nature. Non‐linear body size clines have received less study, and questions remain about how environmental gradients interact to produce non‐linear clines. We examined the body size of the American horseshoe crab (Limulus polyphemus), a widely distributed marine arthropod, and evaluated the hypothesis that temperature and active season length can interact multiplicatively to result in a dome‐shaped distribution.LocationFourteen states in the United States of America and three Mexican states, representing the entire geographic range of the species.MethodsWe compiled environmental data and body size measurements from more than 49,000 individual horseshoe crabs. For each location, we extracted from the literature or calculated from raw data the mean male prosoma width and the mean female prosoma width. We applied a general additive modelling (GAM) approach to characterize the body size cline, test a hypothesis regarding temperature and season length, and explore evidence for the influence of additional environmental factors.ResultsModel results indicate temperature and season length could act multiplicatively to produce dome‐shaped clines, and these findings align with and quantify previous anecdotal reports of a strong dome‐shaped body size cline across latitude for horseshoe crabs.Main ConclusionsActive season length appears to become relatively more influential on horseshoe crab body size in the northern part of their range, while temperature effects per se appear to dominate in southern latitudes. For horseshoe crabs, the pattern of size variation is consistent with the predictions of Optimal Resource Allocation models, but more study is needed to elucidate mechanistic underpinnings. Considering climate change projections, results from our study suggest future shifts in horseshoe crab body sizes.

Rising surface temperatures lead to more frequent and longer burrow retreats in males of the fiddler crab, Minuca pugnax

The fiddler crab Minuca pugnax occupies thermally unstable mudflat habitats along the eastern United States coastline, where it uses behavioral thermoregulation, including burrow retreats, to manage body temperature (Tb). We explored the relationship between frequency of burrow use and environmental conditions, including burrow and surface temperatures, relative tidal height, and time of day, by twenty male M. pugnax in breeding areas around Flax Pond, New York, USA. We found a highly significant positive correlation between burrow use and surface temperature, with a clear shift to longer times underground above 32 °C degrees. We also experimentally heated live crabs in the laboratory and allowed them to retreat into cooled artificial burrows while continuously measuring Tb. Laboratory data on cooling times were compared to field observations of burrow retreat durations. The median burrow duration in the field of 2.74 min was enough time for our laboratory crabs to capture over 70% of the cooling potential of artificial burrows 10 or 15 °C below Tb. Because crab bodies in burrows experience exponential declines in Tb due to Newton's law of cooling, there are diminishing returns to remaining in a burrow, and many crabs probably leave before coming to equilibrium. For M. pugnax, burrow retreats reduce time spent feeding and courting, activities that only occur on the surface. Current concerns about the impacts of climate change on animals include whether compensatory mechanisms, like more frequent and longer burrow retreats, will come at the cost of other behaviors necessary for survival and reproduction.

Incorporating species-specific morphology improves model predictions of thermal and hydric stress in the sand fiddler crab, Leptuca pugilator

Understanding where and why organisms are experiencing thermal and hydric stress is critical for predicting species' responses to climate change. Biophysical models that explicitly link organismal functional traits like morphology, physiology, and behavior to environmental conditions can provide valuable insight into determinants of thermal and hydric stress. Here we use a combination of direct measurements, 3D modeling, and computational fluid dynamics to develop a detailed biophysical model of the sand fiddler crab, Leptuca pugilator. We compare the detailed model's performance to a model using a simpler ellipsoidal approximation of a crab. The detailed model predicted crab body temperatures within 1 °C of observed in both laboratory and field settings; the ellipsoidal approximation model predicted body temperatures within 2 °C of observed body temperatures. Model predictions are meaningfully improved through efforts to incorporate species-specific morphological properties rather than relying on simple geometric approximations. Experimental evaporative water loss (EWL) measurements indicate that L. pugilator can modify its permeability to EWL as a function of vapor density gradients, providing novel insight into physiological thermoregulation in the species. Body temperature and EWL predictions made over the course of a year at a single site demonstrate how such biophysical models can be used to explore mechanistic drivers and spatiotemporal patterns of thermal and hydric stress, providing insight into current and future distributions in the face of climate change.

Studies on modulation of hemocyte surface antigen through agglutination reaction under arsenic toxicity in edible mudcrab (Scylla serrata)

Scylla serrata (Crustacea: Decapoda), which is widely spread on the intertidal mudflat of West Bengal, India's Sundarbans Biosphere Reserves, is a potential aqua crop and an economically significant edible species. One of the larger crab groups in the mangrove swamp of the Sundarbans is thought to be this one. The S. serrata's multifaceted immune response is directly tied to its diverse habitat and survival technique. It lives in dangerous surroundings and is constantly in danger of physiological stress brought on by various xenobiotics, such as arsenic. By producing a number of polyclonal antisera in rabbits (New Zealand White, albino), the study attempted to evaluate the surface antigen against crab hemocytes and murine lymphocytes. Control hemocytes and hemocytes treated to 1 ppm expressed very identical reactivity to antihemocyte sera for the agglutination reaction. The control results, however, shifted when exposed to 2 and 3 ppm of sodium arsenite, indicating arsenic-induced hemocyte surface modification. The agglutination reaction from the control sets of hemocytes that reacted with murine anti-lymphocyte sera gradually, shifted as the quantity of sodium arsenite in the medium of the treatment sets increased. The maximum equivalence zone of murine lymphocyte and hemocyte agglutination 98.6% and 99% respectively suggested a potential epitope sharing between two phylogenetically separate species. The situation may lead to a possible alteration of immune status and make opportunity for pathogenic foreign invaders within the mud crab body. Chronic arsenic exposure indicated a steady decline of edible and demandable S. serrata in the natural habitat of Sundarbans.

Biometric and gonadosomatic indices and chemical constituents of edible tissues and exoskeletons of Callinectes amnicola and their potential for reuse in the circular economy paradigm

The study investigates some biological indices and chemical compositions of Callinectes amnicola and their potential for reuse in the context of the circular economy paradigm. The total of 322 mixed-sex C. amnicola collected over a period of six months was examined. The morphometric and meristic characteristics were estimated for biometric assessment. The gonads were obtained from the female crabs for gonadosomatic indices. The shell was obtained using the hand removal technique by detaching it from the crab body. The edible and shell portions were processed separately and subjected to chemical analysis. Our findings showed that females had the highest sex ratio across the six months. The slope values (b) for both sexes exhibited negative allometric growth across all months since the slope values obtained were less than 3 (b < 3). The values obtained for Fulton’s condition factor (K) of crabs in all examined months were greater than 1. The edible portion had the highest moisture level at 62.57 ± 2.16% and varied significantly (P < 0.05). The high amount of total ash obtained in the shell sample showed that ash is the main mineral present in crab shells and showed a significant difference (P < 0.05). The shell sample had the highest concentrations of Na and CaCO3. Based on the findings of this study, it was observed that the shell waste contains some essential and transitional minerals (Ca, CaCO3, Na, and Mg) and can be utilized as catalysts in several local and industrial applications, such as pigments, adsorbents, therapeutics, livestock feeds, biomedical industries, liming, fertilization, and so on. Proper valorization of this shell waste should be encouraged rather than discarding it.

Effects of dietary isoleucine level on growth and expression of genes related to nutritional and physiological metabolism of swimming crab (Portunus trituberculatus)

A six-week feeding trial was conducted to evaluate the effects of dietary isoleucine level on growth, myofiber histology, and mRNA levels of genes related to amino acid, glucose and lipid metabolism in swimming crab (Portunus trituberculatus). Six isonitrogenous and isolipidic diets (45% protein and 8% lipid) were formulated to contain graded levels of isoleucine (Ile), with the analyzed levels of isoleucine being 0.69%, 1.06%, 1.32%, 1.78%, 2.03% and 2.38%, respectively. A total of 180 crabs (initial weight 16.30 ± 0.01 g) were housed individually in 180 plastic baskets with 30 crabs assigned to each diet, divided randomly into three replicates of 10 crabs. Each crab was fed twice at 08:00 and 18:00 with a daily feeding ration of 6–8% of crab body weight. Eight crabs from each replicate group were sampled and dissected after the feeding trial to provide hemolymph for biochemical analysis, hepatopancreas for proximate composition, amino acid profile enzyme activity, and gene expression, and muscle for proximate composition, amino acid profile and histology. The results indicated that final weight, percent weight gain and specific growth rate increased significantly as dietary isoleucine level increased from 0.69% to 1.78%, and then decreased with further increased dietary isoleucine. Crabs fed the diets with 1.78%, 2.03% and 2.38% isoleucine showed significantly higher muscle protein contents (17.80%, 17.99% and 17.65% of wet mass) than crabs fed lower levels of isoleucine. The highest concentrations of IGF1R and CHH in hemolymph (187.95 and 529.42 pg ml−1, respectively) and hepatopancreas (24.18 and 38.69 pg ml−1, respectively) were observed in crabs fed the diet with 1.32% isoleucine. Hepatopancreas expression levels of genes related to amino acid metabolism, including s6k1, bcat, alt and ast, were up-regulated in crabs fed 1.32% isoleucine compared to the other groups, whereas the expression level of tor decreased as dietary isoleucine increased. Expression levels of genes related to glucose intake, such as pi3k, igf1r and glut1, were significantly higher in crabs fed 1.32% isoleucine compared to crabs fed 0.69% isoleucine. Expression levels of genes related to gluconeogenesis (pepck and g6pase) were significantly higher in crabs fed 0.69% isoleucine than in crabs fed the diets with 1.32% and 1.78% isoleucine. In contrast, expression levels of genes related to glycolysis, including hk, gk and pk, were up-regulated in crabs fed 1.32% isoleucine compared to crabs fed 0.69% isoleucine. Gene expression levels of regulatory factors related to lipid metabolism (foxo, sirt1 and sirt3) were significantly higher in crabs fed 1.32% isoleucine compared to crabs fed the other treatments, while expression levels of genes related to lipolysis (hsl and cpt2) were significantly up-regulated in crabs fed the diets with 1.32% and 1.78% isoleucine. Expression levels of key lipogenesis genes (fas and acc) were down-regulated in crabs fed the diets with 1.32% and 1.78% isoleucine compared to those fed 0.69% isoleucine. Muscle histology indicated that crabs fed the diets with 1.32% and 1.78% isoleucine had significantly lower densities of myofibers (21.67 and 17.33 N/ mm2) compared to crabs fed 0.69% isoleucine. In conclusion, based on percent weight gain, the optimal isoleucine requirement of juvenile swimming crab was calculated to be 1.57% of diet (3.49% dietary protein) by quadratic curve model. Thus, appropriate dietary isoleucine levels (1.32–1.78%) promoted amino acid metabolism and protein synthesis, increased protein deposition, and altered myofiber structure of muscle and, in addition, promoted lipolysis and glycolysis, and reduced lipogenesis and gluconeogenesis in juvenile swimming crab.

Evaluating different diets on the growth performance of mud crab (Scylla serrata)

The purpose of this study was to assess the potential of natural feeds for the sustainable grow-out aquaculture of mud crabs as an alternative to commercially available mud crab feeds. This study employed a completely randomized design that includes five feed treatments including trash fish, African land snail, horn snail, edible frog, and mud snail. There were three replicates for each treatment with three cages each located in a concrete tank with an area of 12m2. Each cage contained one lean crab. The crabs were fed twice a day, at 7 a.m. and 8 p.m. with an amount adjusted to 7% of the crab's body weight. After the first 21 days, all the crabs were harvested by draining out the tank water and the pincers of the crab were tied with a string to enable handling. The results showed that the highest growth performance in weight gain and condition factor was seen in African land snail feed with a feed conversion ratio of 1.38, indicating a high-quality feed. It also showed an impressive ROI of 96.8% which can be confirmed that this kind of feed might be a viable mud crab feed for both commercial scale and industry.

Occurrence and distribution characteristics of aged microplastics in the surface water, sediment, and crabs of the aquaculture pond in the Yangtze River Delta of China

The artificial breeding of freshwater crabs in China has become the main source, accounting for 45.69 % of the total output in 2020. However, microplastics widely exist in ponds due to the addition of meals, and the aging and breakage of plastic tools, and people know little about the occurrence of microplastics in the environment and the tissues of crabs during the cultivation of crabs in ponds. In this study, the abundance and characteristics of microplastics in ponds and crabs were studied finely, and the types of microplastics produced by meals and tools and the aging degree of microplastics in different media were studied in a typical aquaculture experimental base in the Yangtze Estuary of China. After we digested all the samples, there were microplastics in the water, sediment, and inedible part of crabs and crab meals, mainly in fiber shape, with a particle size of 100~300μm, and they have a certain degree of aging. The abundance of microplastics in surface water ranges from 4.4 to 10.8 items/L, and that in sediment ranges from 28.6 to 54.3 items/100 g·dry weight sediments. The average abundance of microplastics in crabs was 23.9 ± 15.9 items/individual. The content of microplastics in crabs' intestinal tissue was the highest, followed by gills and hepatopancreas. At the same time, the microplastics found in crabs were positively correlated with crab body weight and negatively correlated with hepatopancreas index. The results show that in the process of artificial breeding pond feeding, microplastics will be released from the process of meals dissolving in water, and fall off due to wear and tear during the use of tools. Microplastics found in the water, sediments and the tissues of crabs were all aged. Humans have a risk of ingesting microplastics when they eat the tissues of nonedible parts of crabs.

New Records of the Hydrozoan Coryne hincksi Bonnevie, 1898 on Red King Crabs in the Barents Sea

Coryne hincksi Bonnevie, 1898 (Cnidaria, Hydrozoa) is a rare corynid hydrozoan that was first found in the coastal Barents Sea on the surface of other hydrozoan species and on the body of spider crabs in 1913. After the introduction of red king crabs into the Barents Sea in the 1960s and their range expansion and population growth, colonies of C. hincksi were registered on this host as well. In this paper, we update a list of C. hincksi records on red king crabs and present a detailed description. Also, for the first time, we provide quality photographs of a living colony of this species. Despite relatively low prevalence rates (1.4–3.2% in certain years), currently in the Barents Sea, C. hincksi occurs on crustaceans thus exhibiting a predominantly symbiotic lifestyle.

Preparation and Characterization of Flavored Sauces from Chinese Mitten Crab Processing By-Products

To achieve high-value utilization of Chinese mitten crab processing by-products, different types of sauces were prepared using crab legs (CLs) and crab bodies (CBs). Two processing methods, enzymatic hydrolysis and enzymatic hydrolysis coupled with the Maillard reaction, were employed to prepare these sauces. An electronic nose (E-nose) and electronic tongue (E-tongue) were used to measure the changes in the taste and odor, an automatic amino acid analyzer was used to measure the amino acid content, and a headspace solid-phase microextraction GC/MS (HS-SPME-GC/MS) was used to analyze the volatile compounds, qualitatively and quantitatively. The results showed that the sour, bitter, and other disagreeable odors of the enzymatic hydrolysis solution (EHS) were reduced following the Maillard reaction; meanwhile, the umami and saltiness were considerably enhanced. The quantity of free acidic amino acids with an umami and sweet taste in the CL and CB sauces after enzymatic hydrolysis and the Maillard reaction was substantially higher than that in the homogenate (HO). The Maillard reaction solution (MRS) produced more volatile compounds than the HO and EHS, such as aldehydes, pyrazines, ketones, etc. These compounds not only impart a unique flavor but also have antioxidant capabilities, making them a prototype for the high-value utilization of crab processing by-products.

Tidal periodicity of molting in giant mud crab, Scylla serrata (forskål, 1775)

Molting is the most crucial phase in the life cycle of mangrove crabs, leading to mortality in various culture systems. As a result of this exigency, this study was conducted to offer a cue in molting using the tidal cycle as one of the visible events in a natural context. Monitoring was carried out at every 1-hour interval (24 hours) day and night for 57 days to check for molting while taking into account key environmental elements such as tidal cycles, water current speed, and flow rate. The results showed that 70.6% of molting happened during high tide, with 93.8% of it occurring at night and 6.3% during the day. By contrast, only 29.4% occurred during low tide, showing a significant difference (T-test = 0.011, p &lt; 0.05) between mean molts. Hence, the highest molting rate (88.2%) was observed between tidal episodes between the neap and middle cycles, with the middle tide (55.9%) occurring at 12.4±0.9 m/s, neap tide (32.4%) occurring at 16.8±2.0 m/s, and spring tide (11.8%) occurring at 9.5±1.2 m/s. Molting occurs at high tide because crabs' rheotactic behavioral responses to incoming new water help the crab's body fill with air and water throughout the molting process. Mangrove crabs employ their tidal periodicity of molting as a defense strategy against potential predators and mortality, and it can be used as a molting indicator in many culture systems.

Morphometric characteristics of red crab (Thalamita spinimana) in Dompak Tanjungpinang Waters, Riau Islands

The morphometric characteristics of the red crab (Thalamita spinimana) have not been widely studied. This research was conducted from March to May 2021 in the waters of Dompak Tanjungpinang, Riau Islands. Each sample obtained directly measured the morphometric part using a caliper or calipers with an accuracy of 0.05 mm and the crab body weight was also weighed using a digital scale with an accuracy of 0.1 g. The samples obtained during the study were 119 crabs, of which 84 female red crabs and 35 male red crabs. The carapace width range for female crabs is 55.40 – 88.32 mm, while in male crabs the carapace width range is 16.35 and 34 individuals 68.96 – 90.94 mm. The weight of female red crabs is in the range of 50.0 – 103.6 g, while the weight of male crabs is in the range of 49.0 – 142.8 g.

Impact of the acanthocephalan parasite Profilicollis altmani on the fecundity of its crustacean intermediate host, the Pacific mole crab, Emerita analoga

AbstractParasites may influence their hosts in multiple ways, ranging from physiological changes and behavioral modifications, to altering life history traits. One fitness component that is often considered in relation to parasitism is host fecundity. The larval acanthocephalan parasite, Profilicollis altmani, commonly infects the Pacific mole crab, Emerita analoga; yet this parasite's effect on the crab's fecundity is unknown. Consequently, we examined the effects of acanthocephalan parasitism on the fecundity of this mole crab species. Crabs were collected from the swash intertidal zone in Monterey Bay, CA, and the following parameters were quantified: crab body size (carapace length) and weight, egg‐bearing status (nongravid and gravid), egg number and diameter, total volume and weight of egg mass, and their developmental stages (from newly laid eggs to recognizable zoea larval stage). Parasite prevalence, intensity of infection, and body size of larval cystacanths (measured as volume) were assessed. Host fecundity was positively correlated with both body size and body weight. No differences in egg weight were found between uninfected and infected crabs. Similarly, no difference in crab body weight at various embryonic developmental phases was documented between uninfected and infected crabs. Cystacanth volumes in infected nongravid and infected gravid crabs were not significantly different. Our study suggests that the parasite P. altmani does not have any appreciable effect on the fecundity of E. analoga and that female mole crabs undergo normal reproduction and maintain robust population sizes in their natural environments. Our findings thus appear to moderate the pervasive notion of a major impact of parasitism on host reproduction.

Species diversity and molecular taxonomy of symbiotic crustaceans on Portunus pelagicus (Linnaeus, 1758) in Vietnam, with remarks on host records and morphological variation

The blue swimming crab (Portunus pelagicus (Linnaeus, 1758)) is an economically and ecologically important species in Vietnam, and a potential subject for aquaculture as well. More than 400 individual crabs were collected along the Vietnamese coastline and examined for ectosymbiotic crustaceans. Two molecular markers (28S rRNA and COI mtDNA) were applied for species delineation. Seven species were reported and described, of which six are cirripede barnacles (Thecostraca, Thoracia); and one parasitic copepod Choniosphaera indica Gnanamuthu, 1954 (Copepoda, Podoplea). Four species (Chelonibia testudinaria (Linnaeus, 1758), Semibalanus sp., Octolasmis neptuni (MacDonald, 1869), and Dianajonesia tridens (Aurivillius, 1894)) were the first records for both host and location. The symbiotic crustaceans occupy specific niches on the crab body, and vary in their infestation status. Molecular taxonomy of symbiotic crustaceans was classified and confirmed based on sequence similarity and phylogenetic analyses.

Unique Behavioral Strategies Adopted by Gravid Ghost Crab Ocypode gaudichaudii to Overcome Dehydration Stress while Minimizing Predation Risks.

Semi-terrestrial crabs require continual access to water to maintain life-sustaining processes such as circulation and feeding. When they emerge from their burrows during low tide to forage, they face the problem of dehydration as they leave the dampness of their burrows. While foraging above ground, water uptake is elicited through capillary action via the hydrophilic setae near the base of the crab's body. Extruded eggs that are borne on the abdominal flap of females tend to obstruct the contact of the setae with the wet sediment. The behavioral adaptations that enable the gravid female painted ghost crab, Ocypode gaudichaudii, to overcome dehydration stress and minimize predation risks at a sandy shore in Playa Venao, Panama were studied using field observations. Comparison of the morphometric measurements of setal tufts between 30 male and 30 female crabs was made to determine if there were morphological adaptations. Analysis of the water uptake behavior from video footage showed that gravid crabs spent a longer duration on water uptake than crabs that did not carry eggs. For the first time, masquerading behavior of a gravid O. gaudichaudii was observed, in which the crab minimized predatory detection by freezing its movement next to a stone enroute to the lower shore during the day. There was no sexual dimorphism in the length and width of the setal tufts between the male and female adult crabs. The results of this study provide the first evidence that the water-uptake behavior in gravid O. gaudichaudii is dependent on behavioral adaptations, as setal tuft morphology does not differ between the sexes.

Burrow Morphology of Brachyuran Crab Dotilla blanfordi Alcock, 1900 from Gulf of Khambhat, Gujarat, India

The present study was conducted to understand the burrow morphology of brachyuran crab Dotilla blanfordi Alcock, 1900 at Dandi beach located in Gulf of Khambhat of Gujarat state, India. Burrows were selected randomly and their opening diameter was recorded. Diluted resin was poured in the burrows to generate burrow cast. If the occupant crab emerges out of the burrow, it was captured and carapace width and gender was recorded. The shapes of complete burrow casts were identified and measurements of various morphological characters of burrow cast were recorded. Total 7 different burrow shapes were identified, out of which single tube burrow was the most common as compared to other burrow shapes. The crab carapace width showed significant relationship with burrow opening diameter, burrow depth, burrow length and burrow volume. Juveniles (3.45 mm CW) were making burrow of all the seven shapes. Burrow depth, length and volume were significantly higher in adult crabs as compared to juveniles. No significant variation was observed between burrows of male and female individuals. The present study showed that burrow morphology is highly affected by the crab body size and also varies significantly with different life stages of the crab. Juveniles make shallow and simple burrows as their smaller gill areas stores lesser amount of respiratory water which needs to be changed frequently. However, adults make complex burrows to perform various tasks including copulation and reproduction.

Signs of claw asymmetry appear in a homochelate crab

Lateral asymmetry is observed widely among vertebrates and invertebrates. It appears in various aspects, such as morphological structure, or the preferential use of body parts. Many studies have focused on animal handedness and its developmental process. This is especially true in crabs with asymmetrical claws (heterochelate), while there are few studies on handedness (claw laterality) in crabs with symmetrical claws (homochelate). In this study, we analyzed the claw symmetry of the Chinese mitten crab (Eriocheir sinensis) by comparing the ratio of chela height to length (HL- ratio), and we also analyzed the correlation between cheliped morphology and weight, crab body weight, physiological indices and closing force. The relationship between handedness and behavior of the crabs was further analyzed. The results showed that the morphology of the chelipeds was not symmetrical. The left chela of male crabs and the right chela of female crabs were stubbier. The closing force was positively correlated with the HL- ratio. Moreover, the closing force of the right cheliped was significantly greater than that of the left cheliped in females. In the comparison of behaviors between the lateral group (crabs with significantly greater closing force on the left or right claw) and non-lateral group (crabs with roughly the same closing force on their left or right claws), we identified that the lateral group showed more significant lateralization than the non-lateral group in hiding behavior. Further studies are needed to investigate the mechanism or evolutionary drivers of asymmetric claws in homochelate crabs.

‘Photography’ as a useful method for estimating the density, sex-ratio and body size of the surface-active Austruca perplexa (H. Milne Edwards, 1852) (Brachyura, Ocypodidae)

Abstract Estimations of crab density, sex-ratio, and body sizes are difficult. Though the ‘burrow excavation’ method is widely used to estimate these parameters in surface-active crabs, it is destructive to crab populations. Therefore, an alternative, non-destructive method is desirable. This study compared the non-destructive ‘photography’ method with the ‘burrow excavation’ method in a fiddler crab (Austruca perplexa (H. Milne Edwards, 1852)) population. Twenty 0.25 m2 quadrats were set out and 4 photos were taken of the surface-active crabs in each quadrat. All crab burrows were then excavated, and the crabs were collected to estimate their numbers, sexes, and body and claw sizes. Afterward, the photographs were analysed to estimate the same parameters by using the GIMP program. These parameters were then compared between the two methods. The results showed that these parameters were not different between the methods compared. This study thus reveals that the ‘photography’ method could safely be used instead of the ‘burrow excavation’ method, and yield the same results.