Control Crabs Research Articles

Exposure to Lead (Pb) influences the outcomes of male-male competition during precopulatory intrasexual selection

Male-male competition is a component of Darwin’s theory of precopulatory intrasexual selection, where males compete for access to resources important for reproduction and successful males pass on traits that endow greater competitive ability to their offspring, thereby exaggerating the trait(s) over evolutionary time. Metals, such as lead (Pb) often occur in urban mangrove forests, where shore crabs reside, and being neurotoxic may cause sub-lethal effects on behaviour. In this study, we asked whether exposure to Pb influences the outcomes of male-male competition in the Semaphore crab, Heloecius cordiformis, thereby altering outcomes of intrasexual selection. Crabs were exposed to an environmentally relevant, and a behaviourally relevant, concentration of lead (i.e. Pb, 10 µg/L and 100 µg/L respectively) under laboratory conditions for 96 h and subsequently allowed to compete for burrow ownership in experimental arenas. Exposed crabs (100 µg/L) were less successful than control crabs in chela size-matched paired competitive interactions, spent less time in burrows and predominantly lost burrow ownership. Further, exposure to Pb contamination (both 10 µg/L and 100 µg/L) negated the chela size advantage in size-asymmetric competitive interactions. This contaminant-induced loss of size-related competitive advantage may result in relaxation in selection pressure on body size and smaller male carapace widths and especially male chela lengths in contaminated locations. Assessment of a range of locations in the wild found a consistent pattern of metal-associated size declines in more contaminated locations for males, but not for females.

Dietary supplementation of Roseovarius litoreus improves survival and immune defense of the swimming crab Portunus trituberculatus

The aquaculture of the swimming crab Portunus trituberculatus is challenged by vibriosis, and Rhodobacteraceae strains play a crucial role in maintaining gut health and enhancing the immunity of crustaceans. In this study, we investigated the effects of dietary supplementation of Roseovarius litoreus, a member of Rhodobacteraceae, on the survival and immune defense of the swimming crab. The results showed that 60-day dietary supplementation of R. litoreus resulted in a marked increase in the mRNA expression of gut ZO-1. Meanwhile, R. litoreus increased zero-radius operational taxonomic unit (ZOTU) richness and changed the gut bacterial community, which was manifested by the enriched Carboxylicivirga and Roseovarius and depleted Photobacterium and Vibrio, thereby upregulating functional potentials of the gut bacterial community in the immune system and biosynthesis of other secondary metabolites. After a 72-h V. parahaemolyticus challenge, R. litoreus-supplemented crabs had an increased survival rate, reduced histological damage of hepatopancreas and gut, and improved expressions of immune-related genes and lysozyme activity. Moreover, R. litoreus-supplemented crab gut still harbored more Carboxylicivirga and Roseovarius but had fewer Vibrio gene copies than control crabs, which led to similar changes in functional potentials. Notably, all ZOTUs that were positively correlated with immune-related genes and lysozyme activity belonged to Bacteroidetes, Bacteroidales, or Carboxylicivirga. Taken together, we highlight the probiotic role of R. litoreus in the survival and immune defense of the swimming crab. These findings may contribute to the development of indigenous bacteria of the swimming crab as potential probiotics for the control of vibriosis.

A multibiomarker approach to assess the effects of a BPA analogue-contaminated diet in the crab Carcinus aestuarii

Bisphenol A analogues are largely used plasticisers that are going to replace bisphenol A in many sectors. Due to this replacement, their discharge and presence in the marine coastal areas are increasing, with unknown consequences for organisms and the trophic chain. This study assessed the effects of three different bisphenols (BPAF, BPF and BPS) - alone or as a mixture - provided via food (exposed clams) to the crab Carcinus aestuarii. First, clams were exposed for two weeks to 300 ng/L of each of the three bisphenols and their mixture (100 ng/L of each) to allow the bioaccumulation of the contaminants in bivalves. Then, crabs were fed for two weeks with BPA analogue-exposed clams, while unexposed clams were used to feed control crabs. After 7 and 14 days, haemolymph, gills and hepatopancreas were collected from crabs to measure a battery of biomarkers indicative of cytotoxicity, oxidative stress and damage, neurotoxicity, physiological performance (respiration and excretion rate) and electron transport system activity. Lastly, bioaccumulation of BPA analogues was assessed by UHPLC-HRMS in crabs. Our findings revealed that BPA analogue-exposed clams were able to alter total haemocyte count, haemocyte size and their proliferation. The activity of immune enzymes, such as phosphatases and phenoloxidase was altered. Moreover, we observed an impairment of antioxidant and detoxifying enzymes like SOD, CAT, GST and GPX activities. Alterations of metabolism-involved enzymes and physiological parameters and increased oxidative damage to macromolecules like proteins, lipids, and DNA were also observed in crabs. Among BPA analogues, only bioaccumulation of BPAF, which has the highest Logkow value among the tested bisphenols, was evidenced in crabs. Overall, the obtained results indicated that crabs, under the tested experimental conditions at least, underwent alterations in cellular, biochemical and physiological responses following a diet of bisphenol-exposed clams, suggesting a potential ecotoxicological risk in the marine food chain.

The impact of chasing stress on the metabolism of the Atlantic Ghost Crab Ocypode quadrata (Fabricius, 1787).

Ocypode quadrata, a Ghost crab species found along the western Atlantic coast, is considered a bioindicator of anthropogenic impact on sandy beaches. Ghost Crabbing, a touristic activity in which ghost crabs are chased just for fun, is a potentially threatening activity for this crab. In crustaceans, metabolites such as glucose and lactate, and the gene expression of crustacean hyperglycemic hormone (CHH) and heat shock proteins (HSPs) increase when the animals are exposed to several types of stress, including alterations in temperature, salinity, or exposure to xenobiotics. This work was developed to identify if being chased by humans would affect these markers of stress in this species of crab. The effects of chasing stress on hemolymph and tissue metabolites and the gene expression levels of CHH and HSP70 were investigated. The levels of lactate in the hemolymph of stressed crabs were six times higher than those of control crabs immediately after chasing and decreased progressively during recovery, indicating an active anaerobic metabolism during the stress. On the contrary, glucose levels in the hemolymph of the stressed crabs increased progressively from 30 to 60 min after chasing, indicating an inverse correlation between glucose and lactate and the conversion of lactate to glucose by gluconeogenesis. In stressed crabs, the levels of triglycerides in the hemolymph decreased 30 min after chasing, while the opposite tended to occur in the hepatopancreas, indicating that during recovery, the crabs use triglycerides as energy source to sustain aerobic metabolism. Finally, this study demonstrates that ghost crabs are stressed by minimum human contact and that "ghost crabbing" must not be encouraged as a tourist activity.

The first description of the blue swimming crab (Portunus pelagicus) transcriptome and immunological defense mechanism in response to white spot syndrome virus (WSSV)

In the global shellfish farming industry, white spot syndrome virus (WSSV) is a major cause of mortality and a significant factor in economic losses. However, information on molecular immune responses to WSSV in blue swimming crabs (Portunus pelagicus) has never been reported. First, viral loads were measured in the gills, hepatopancreas, intestines, subcuticular epithelium and hemocytes of blue swimming crabs (50 ± 10 g) (n = 4) after WSSV induction at 0, 24, 48 and 96 h post injection (hpi). A significant increase in WSSV particles was observed in gills at 48 and 96 hpi, as supported by histopathology. To further investigate the acute immune response to WSSV, total RNA from the same gill tissues at 0, 24, and 96 hpi was used to construct 16 high-quality RNA-seq cDNA libraries. In summary, 162,740 unigenes were discovered in these transcriptomic libraries analyzed with the GO, KO, KOG, NR, NT, PFAM and SwissProt databases. Intensive sequence analysis against control crabs using three major categories of gene oncology (GO) of DEGs, biological processes (BPs), molecular functions (MFs), and cellular components (CCs), indicated that induction of WSSV in blue swimming crabs strongly affected the immune responses of the target animals significantly during the early stages of infection from 24 to 96 hpi. Furthermore, KEGG identified approximately twenty biological pathways of gene expression that were both downregulated and upregulated. Interestingly, at 24 and 96 hpi, several immune-related genes involved in virus defense in the blue swimming crab, particularly crustin 2, chitinase, anti-lipopolysaccharide, proteinase inhibitor, and lysozyme, were highly expressed during the WSSV early infection stages. At the same time, viral mRNA transcripts, including WSV289, WSV343, WSV306, deoxyuridine 5’ triphosphate nucleohydrolase, RING finger containing E3 ubiquitin-protein ligase WSV403 and WSV404, were recorded in the top twenty upregulated genes. Moreover, some immune-responsive genes related to growth development, such as chitinase, tubulin alpha and beta chains, trypsin, and the cathepsin family, were also differentially expressed during these periods. Expression validation of 20 upregulated and 11 downregulated immune-related genes using qRT‒PCR showed similar patterns with transcriptome information. Overall, the data showed that during WSSV infection, a number of immune-, metabolism-, and growth-related pathways were activated, and several of the pathways involved differed depending on the stage of virus invasion. These findings could effectively help us better understand the impact of WSSV on the physiology of blue swimming crabs and serve as a valuable reference for future research on the immune system and disease control in this target species.

Extracellular vesicle signatures and protein citrullination are modified in shore crabs (Carcinus maenas) infected with Hematodinium sp

ABSTRACT Epizootiologists recurrently encounter symbionts and pathobionts in the haemolymph (blood equivalent) of shellfish. One such group is the dinoflagellate genus Hematodinium, which contains several species that cause debilitating disease in decapod crustaceans. The shore crab Carcinus maenas acts as a mobile reservoir of microparasites, including Hematodinium sp., thereby posing a risk to other co-located commercially important species, e.g. velvet crabs (Necora puber). Despite the widespread prevalence and documented seasonality of Hematodinium infection dynamics, there is a knowledge gap regarding host-pathogen antibiosis, namely, how Hematodinium avoids the host’s immune defences. Herein, we interrogated the haemolymph of Hematodinium-positive and Hematodinium-negative crabs for extracellular vesicle (EV) profiles (a proxy for cellular communication), alongside proteomic signatures for post-translational citrullination/deimination performed by arginine deiminases, which can infer a pathologic state. Circulating EV numbers in parasitized crab haemolymph were reduced significantly, accompanied by smaller EV modal size profiles (albeit non-significantly) when compared to Hematodinium-negative controls. Differences were observed for citrullinated/deiminated target proteins in the haemolymph between the parasitized and control crabs, with fewer hits identified overall in the former. Three deiminated proteins specific to parasitized crab haemolymph were actin, Down syndrome cell adhesion molecule (DSCAM), and nitric oxide synthase – factors that contribute to innate immunity. We report, for the first time, Hematodinium sp. could interfere with EV biogenesis, and that protein deimination is a putative mechanism of immune-modulation in crustacean-Hematodinium interactions.

Acute exposure to a neem based biopesticide and mahua oil cake changes haemocyte parameters in freshwater crab, Varuna litterata (Decapoda, Crustacea)

Present study aims to evaluate the immunotoxic effects of two biopesticides, Nimbecidine Plus (a neem biopesticide) and mahua oil cake (MOC) on the haemocyte populations of a freshwater crab, Varuna litterata after acute exposure. Four-day static renewal bioassay test was performed where sixteen healthy adult male crabs were exposed to 96-h LC50 values of Nimbecidine Plus (0.006284 ppt) and MOC aqueous extract (7.631 ppt) separately in the laboratory condition. Control groups were maintained throughout the experimental period without any biopesticide exposure. Various haemocyte parameters such as total count (THC), differential count (DHC), haemocyte density, cytomorphological anomalies and reactive oxygen species (ROS) were measured in the biopesticides-exposed and control crabs after 24, 48, 72, and 96 h of exposure. After treatment with Nimbecidine Plus and MOC, several cytomorphological deformities (cytoplasmic and nuclear membrane disintegration, chromatin condensation, pyknosis, karyorrhexis, karyolysis, nuclear vacuolation, altered cell shape, cellular coagulation, cytoplasmic discharge, vacuolation) were observed in hyalinocytes, small granule haemocytes and large granule haemocytes with modulation of their relative percentages at different exposure times. THC, DHC, haemocyte density and ROS levels were significantly altered (p < 0.05) in biopesticides-exposed crabs at different exposure periods. The toxicity of both biopesticides did not persist throughout the entire exposure time. Nimbecidine Plus exhibited nonlinear toxic impacts on different haemocyte parameters at initial, mid and higher exposure periods whereas MOC showed linear toxic effects mostly at initial exposure time. In comparison to MOC, Nimbecidine Plus showed higher immunotoxic effects in V. litterata. Outcome of this experiment might provide useful information to understand the immune responses of V. litterata against biopesticide toxicity.

Utilization of Feed and Growth Performance of Mud Crabs: The Effect of Herbal Extracts as Functional Feed Additives

This study aimed to analyze the effect of herbal extracts as functional feed additives on the utilization of feed and growth performance of orange mud crabs (Scylla olivacea). The test animals used were 60 crabs for each treatment dose. The crabs are kept individually in a crab box which was placed on a floating bamboo raft. This was to enable floating on the surface of the pond water which had a depth of ±80 cm. The treatments tested were four doses of a combination herbal extract from Morus alba, Curcuma xanthorrhiza, and Boesenbergia rotunda, namely 0, 200, 400, 600 mg kg-1 of feed. Formulated feed with the protein content of 41.93%, fat 7.43%, Nitrogen Free Extract (NFE) 29.33%, and crude fiber 7.82% was given at a dose of 5% body weight every day. Based on one-way ANOVA, the results showed that the dose of herbal extracts influences the feed utilization and growth performance of mud crabs. The dose of herbal extract 600 mg kg-1 of feed provided higher feed utilization and growth performance (LSD Test: P&lt;0.1). Significant differences were found between feed utilization and growth performance of mud crabs after molting and non-molting. In molting mud crabs, treatment with herbal extract 600 mg kg-1 obtained an average weight gain of ±60.73 from the initial weight, compared to control crabs (without herbal extracts) gaining an average weight gain of ±43.73%. However, in non-molting crabs, ±5.44 and ±6.42 weight gain was observed, respectively. Significant differences also occurred between treatments for specific growth rates, feed consumption, feed efficiency, and condition factors. These results provided information that herbal extracts are potentially as feed additives to increase feed utilization and growth performance, as well as stimulate molting in crab cultivation.

Effects of water acidification on immune responses of the gercacinid, Cardiosoma armatum (Herklots, 1851)

The biological response to chemical pollutants reflects the acid–base status of an aquatic ecosystem. The gercacinid, Cardiosoma armatum (75±0.1 g) was exposed to acidified waters to evaluate the effects on its immune parameters. The crabs were exposed to pH 4.0, 5.0, 6.0 and 7.8 (control) for 28 days. The hematological parameters of control crabs and crabs exposed to varied doses of acidified water indicated a marked reduction. Significant (p&lt;0.05) higher alkaline phosphatase and albumen were obtained in pH 4.0, 5.0 and 6.0 compared to control; other values were mostly similar to control. The highest superoxide dismutase (SOD) (252.61±0.06 min/mg pro) was recorded in control group, while highest CAT activity (2.08±0.16 min/mg protein) was recorded in crabs exposed to pH 4 treatment. Furthermore, the control group's SOD activity was significantly higher than the exposed groups. With a lower pH, the quantities of malondialdehyde increased substantially and were significantly different from the control group. While these findings demonstrate that changes in pH have limited impact on energy use, decreasing immune system conditions show that C. armatum is susceptible to pH variations and may be influenced in aquaculture, where a pH drop is more prominent.

Sublethal behavioral and physiological effects of claw removal on Jonah crabs (Cancer borealis)

Jonah crabs (Cancer borealis) have been caught as incidental bycatch for over 80 years, but in recent years they have become a targeted fishery, especially in Southern New England where the American lobster (Homarus americanus) population has declined, and harvesters have begun seeking alternative fisheries. This shift has prompted the need for more biological data for Jonah crabs so that this expanding fishery can be managed more effectively. For example, in some areas of its range males have both of their claws removed at sea and only the claws are landed; however, little is known about what happens to the crabs that survive this practice. The focus of this study was to evaluate the impacts of claw removal on Jonah crab mating success, feeding ability and locomotion. In mating trials, all males, regardless of claw status, managed to successfully mate with females that molted while they were paired together (clawed n = 4, claws removed n = 8). When Jonah crab activity was measured in the laboratory, crabs with intact claws were significantly more active than crabs with both claws removed (clawed: 25.0 ± 8.0% of each hour active, 1 claw removed: 18.1 ± 7.3% of each hour active, clawless: 13.6 ± 9.04% of each hour active, mean ± SD). Similarly, based on data from a tag/recapture experiment, crabs with both claws missing moved about half the distance per day as control crabs, between the time they were released and first recaptured (clawed: 117 ± 43.1 m/day, clawless: 50 ± 11.3 m/day, mean ± SE), although the difference was not significant. These changes in locomotion could be the result of the blood loss associated with claw removal. We found that hemocyanin levels dropped significantly after the removal of both claws and remained so for up to two weeks. Finally, crabs with no claws were able to feed, but they had difficulty opening mussel shells, which might influence their diet in their natural habitat. These data suggest that those Jonah crabs that do survive the claw removal process might be impaired, but should be able to forage, mate, and help sustain the population.

Cadmium is deposited to the exoskeleton during post-ecdysial mineralization in the blue crab, Callinectes sapidus

Despite the fact that cadmium has been reported to be present in crustacean exoskeletons, no study has previously been done to determine when cadmium is deposited to the exoskeleton and what effects cadmium has on the shell-hardening process. This project sought to address these scientific questions using the blue crab, Callinectes sapidus, as the model crustacean. It was hypothesized that cadmium would be incorporated into the exoskeleton during post-ecdysial mineralization through ionic mimicry because of the resemblance between cadmium and calcium ions. To test this, soft shell blue crabs were injected with cadmium chloride, and cadmium content in the exoskeleton was subsequently quantified using ICP-OES. Carbonic anhydrase catalyzes the carbon dioxide hydration reaction, which generates bicarbonate ions essential for calcium carbonate formation in the shell. The effect of cadmium injection on epidermal carbonic anhydrase activity as well as exoskeletal calcification was also investigated. It was found that cadmium injection into post-ecdysial Callinectes sapidus significantly increased cadmium content in the exoskeleton, suggesting that cadmium is deposited to the new exoskeleton during post-ecdysial mineralization. Cadmium administration had no effect on epidermal carbonic anhydrase activity or exoskeletal calcification. Interestingly, magnesium content in the exoskeleton was significantly elevated following cadmium treatment. This is most likely a “pseudo” effect stemming from the cadmium-induced reduction in exoskeleton weight. The fact that cadmium had no effect on exoskeletal calcium and that cadmium decreased the weight of the exoskeleton suggests that cadmium has a detrimental effect on the formation of the organic matrix of the exoskeleton. The presence of cadmium in control crabs and exuviae and the amplification of cadmium content in cadmium-treated crabs clearly show that crab shell is a cadmium repository and can be used as a biomarker for aquatic cadmium pollution.

Invasion history shapes host transcriptomic response to a body-snatching parasite.

By shuffling biogeographical distributions, biological invasions can both disrupt long-standing associations between hosts and parasites and establish new ones. This creates natural experiments with which to study the ecology and evolution of host-parasite interactions. In estuaries of the Gulf of Mexico, the white-fingered mud crab (Rhithropanopeus harrisii) is infected by a native parasitic barnacle, Loxothylacus panopaei (Rhizocephala), which manipulates host physiology and behaviour. In the 1960s, L.panopaei was introduced to the Chesapeake Bay and has since expanded along the southeastern Atlantic coast, while host populations in the northeast have so far been spared. We use this system to test the host's transcriptomic response to parasitic infection and investigate how this response varies with the parasite's invasion history, comparing populations representing (i) long-term sympatry between host and parasite, (ii) new associations where the parasite has invaded during the last 60years and (iii) naïve hosts without prior exposure. A comparison of parasitized and control crabs revealed a core response, with widespread downregulation of transcripts involved in immunity and moulting. The transcriptional response differed between hosts from the parasite's native range and where it is absent, consistent with previous observations of increased susceptibility in populations lacking exposure to the parasite. Crabs from the parasite's introduced range, where prevalence is highest, displayed the most dissimilar response, possibly reflecting immune priming. These results provide molecular evidence for parasitic manipulation of host phenotype and the role of gene regulation in mediating host-parasite interactions.

Assessing the implications of live claw removal on Jonah crab (Cancer borealis), an emerging fishery in the Northwest Atlantic

In the Northwest Atlantic fisheries management is adapting to emerging fisheries. The fishery for Jonah crab (Cancer borealis) is rapidly expanding resulting in a quadrupling of landings over the past 20 years. In response to this increased fishing effort, management plans have begun adopting a suite of regulatory measures, one of which allows the live removal of claws at-sea. The overall goal of this project was to determine if claw removal has an impact on crab mortality. Results from a series of laboratory trials with individual crabs (n = 240) indicate that double-claw removal incurs markedly more mortality (70 %) compared with single-claw removal (51 %). Mortality was significantly correlated with wound size, temperature, and shell condition (GLM, p < 0.05), as well as elevated levels of glucose and lactate in the haemolymph of declawed animals. We also conducted a comparative claw removal trial (n = 40) using both manual- and mechanically-induced (using a declawing tool) methods and showed that mortality in manually declawed crabs (87 %) was much higher than when claws were removed mechanically (40 %, Wilcoxon pairs test, p < 0.0001). Finally, when claws were removed from tagged crabs released in the field (n = 464), four times as many control crabs were recaptured than crabs with claws mechanically removed, and none of the crabs whose claws were manually removed were recaptured (p = 0.0048). Overall, claw removal results in a significant number of mortalities. However, our findings also provide a foundation for future investigations on the sub-lethal effects of claw removal on Jonah crabs as well as the impacts of claw harvesting to improve fisheries management of this rapidly burgeoning fishery.

Effect of a chemical dispersant (Corexit 9500A) on the structure and ion transport function of blue crab (Callinectes sapidus) gills

Chemical dispersants are commercially available mixtures of surfactants and solvents that have become important tools in the remediation of spilled oil. Given the importance of oil to the world economy, the recurring nature of spills, and the prevalence of dispersant use in remediation, there is a critical need to understand potential toxic impacts of dispersants on invertebrate and vertebrate animals. Blue crabs (Callinectes sapidus) play ecologically important roles in the environments they inhabit and support economically important fisheries along the Atlantic Coast and in the Gulf of Mexico. In studies reported here, we assessed the impact of a chemical dispersant, Corexit 9500A, on the structure and ion transport function of blue crab gills. Exposure of blue crabs to Corexit 9500A for 24 h (0–300 ppm in artificial seawater under static conditions) revealed a 24-h lethal concentration 50 (LC50) estimate of 210 ppm. A histological analysis of gills from crabs exposed for 24 h to a sub-lethal concentration of Corexit 9500A (125 ppm) revealed evidence of loss or disruption of cuticle, and an increase in stained amorphous material in the hemolymph spaces of gill lamellae. Quantitative image analysis of stained gill sections revealed the area/length ratio of gill lamellae in crabs exposed to Corexit 9500A (24 h, 125 ppm), was greater than that in gill lamellae from control crabs; the results are consistent with the presence of edematous swelling in gill lamellae from dispersant-exposed crabs. Quantitative PCR was used to measure the relative abundance of transcripts encoding three ion transport proteins (Na+/K+ ATPase, plasma membrane Ca2+ ATPase (PMCA), and sarcoplasmic reticulum/endoplasmic reticulum Ca2+ ATPase (SERCA)) in gills from Corexit-exposed and control crabs. In general, the abundance of transcripts encoding each ion transport protein was lower in gills from dispersant-exposed crabs than in gills from control crabs. The combined results are consistent with the hypothesis that 24-h exposure of blue crabs to a sublethal concentration of Corexit 9500A impacts both the structure and ion transport function of gills.

Sublethal Effects of Organophosphate Chlorpyrifos on Hemato-Immunological Parameters of the Gercacinid Crab, Cardiosoma armatum (Herklots, 1851)

Low insecticide exposure has been shown to cause profound effects on non-target organisms, including crabs. Therefore, the changes in hematological parameters, serum biochemistry and antioxidant enzymes in the Gercacinid crab, Cardiosoma armatum were assessed during 28-day exposure to four concentrations of organophosphate chlorpyrifos (0.003, 0.006, 0.03 and 0.06 mg/l). The results showed a significant (P= 0.0) decrease in packed cell volume and total haemocyte count of the exposure crabs (except in 0.003 mg/l concentration) compared to control group. There were no significant changes in hemocyte sedimentation rate, granulocyte and agranulocyte, although all exposure groups increased in hemocyte sedimentation rate and agranulocyte with respective ranges of 3.00-3.02 mm/hr and 64.00-67.00 %. Except for alkaline phosphatase, there were no significant variation in the biochemical profile of both the control crabs and exposure crabs, although organophosphate chlorpyrifos exposure induced increase in all the measured biochemical parameters. The serum protein level and the activities of the enzymes (superoxide dismutase, catalase and malondialdehyde) were inhibited in exposure groups. The changes in these hemato-immunological parameters of the crabs were suitable biomarkers of a sub-lethal exposure to chlorpyrifos at the concentrations tested, and this will be useful in biomonitoring of aquatic environment.

Survival strategies on a semi-arid island: submersion and desiccation tolerances of fiddler crabs from the Galapagos Archipelago

During tidal cycles, fiddler crabs undergo alternating periods of submersion and desiccation. We compare physiological and biochemical adjustments to submersion and desiccation challenge in two gelasminids from the Galapagos archipelago: the indigenous Leptuca helleri, and Minuca galapagensis. We examine population distributions and habitat characteristics; survival and hemolymph osmolality after 6 h submersion at several salinities, and after 6 or 12 h desiccation; and oxidative stress responses in the hepatopancreas and gills, accompanying glutathione enzyme antioxidant activities, and lipid peroxidation. We provide an integrated biomarker response index based on oxidative stress in each tissue, condition and species. Leptuca helleri occupies a restricted intertidal niche while M. galapagensis is supralittoral. Burrow density in M. galapagensis declined with increasing salinity and decreasing substrate moisture; L. helleri burrow density showed no correlation. After 6 h submersion, L. helleri survived only at 21‰S while M. galapagensis survived from 0 to 42 ‰S. After 6 h desiccation, hemolymph osmolality decreased markedly in L. helleri but increased in M. galapagensis. Antioxidant enzyme activities and lipid peroxidation in the hepatopancreas and gills showed tissue- and species-specific responses to submersion and desiccation challenge. The integrated biomarker response indexes for L. helleri were highest in control crabs, driven by oxidative stress. In M. galapagensis, submersion was the determining factor in both tissues. Minuca galapagensis is a generalist species while Leptuca helleri occupies a more restricted intertidal habitat. The species’ respective physiological limitations and flexibilities provide insights into how fiddler crabs might respond to environmental change on semi-arid islands.

Sublethal effects of malathion insecticide on growth of the freshwater crab Poppiana dentata (Randall, 1840) (Decapoda: Trichodactylidae)

Pesticides can interfere with various aspects of growth and the normal molt cycle of a crustacean. Poppiana dentata (Randall, 1840), an indigenous crab species, spends most of its life cycle in, and proximal to, benthic sediments in which pesticide residues can reside. This study sought to assess the sublethal effects of a locally-used, commercial malathion insecticide on growth aspects of P. dentata. Juvenile crabs were obtained from berried females collected in northwest Trinidad. Young crabs were placed in a control (insecticide-free) treatment and an exposure treatment involving continuous exposure to the malathion insecticide, at 10 µg/L concentration over five months (n = 4 crabs/treatment). Carapace width (CW), length (CL) and intermolt period were recorded and used to derive size increment, specific growth rate (SGR), growth curves and logistic equations. Malathion-exposed crabs exhibited irregular patterns in SGR and size increment. Exposed crabs also exhibited a delay in molting and longer intermolt periods, compared to the control crabs (p < 0.05). Breakpoint (17.5 mm CW) and maximum size (CW = 25.77 (1+exp (1.500-0.056t))-1) for exposed crabs were relatively smaller than those of the control (22.11 mm CW; CW = 34.30 (1+exp (1.774-0.035t))-1). Findings indicate that sublethal exposure to malathion insecticide altered growth patterns in P. dentata, some of which can influence maturity and later cascade into secondary consequences for local populations.

The combined effects of ocean acidification and warming on a habitat-forming shell-crushing predatory crab

In mid rocky intertidal habitats the mussel Perumytilus purpurarus monopolizes the substratum to the detriment of many other species. However, the consumption of mussels by the shell-crushing crab Acanthocyclus hassleri creates within the mussel beds space and habitat for several other species. This crab uses its disproportionately large claw to crush its shelled prey and plays an important role in maintaining species biodiversity. This study evaluated the consequences of projected near-future ocean acidification (OA) and warming (OW) on traits of A. hassleri linked with their predatory performance. Individual A. hassleri were maintained for 10–16 weeks under contrasting pCO2 (~500 and 1400 μatm) and temperature (~15 and 20 °C) levels. We compared traits at the organismal (oxygen consumption rate, survival, calcification rate, feeding rates, crusher claw pinching strength, self-righting speed, sarcomere length of the crusher claw muscles) and cellular (nutritional status ATP provisioning capacity through citrate synthase activity, expression of HSP70) level. Survival, calcification rate and sarcomere length were not affected by OA and OW. However, OW increased significantly feeding and oxygen consumption. Pinching strength was reduced by OA; meanwhile self-righting was increased by OA and OW. At 20 °C, carbohydrate content was reduced significantly by OA. Regardless of temperature, a significant reduction in energy reserves in terms of protein content by OA was found. The ATP provisioning capacity was significantly affected by the interaction between temperature and pCO2 and was highest at 15 °C and present day pCO2 levels. The HSP70 levels of crabs exposed to OW were higher than in the control crabs. We conclude that OA and OW might affect the amount and size of prey consumed by this crab. Therefore, by reducing the crab feeding performance these stressors might pose limits on their role in generating microhabitat for other rocky intertidal species inhabiting within mussel beds.

Effects of serotonin and dopamine on ovarian development in the freshwater crab Travancoriana schirnerae (Brachyura: Gecarcinucidae)

AbstractThe current study explicated the effects of serotonin (5‐hydroxytryptamine, 5‐HT) and dopamine (DA) on ovarian development in the edible freshwater crab Travancoriana schirnerae, distributed in the wetlands of Wayanad. Adult intermoult female crabs in various oogenic stages were administered with 5‐HT and DA, weekly once for four weeks and the ovaries processed for histological and biochemical analyses. The results indicated that 5‐HT induced ovarian maturation by a significant rise in ovarian index, mean oocyte diameter, oocyte proportion values, gonial proliferation, folliculogenesis and degree of yolk deposition while DA showed a significant decline in the aforesaid parameters thus delaying ovarian growth when compared to the untreated controls. Further biochemical analyses confirmed the 5‐HT triggered ovarian growth as evinced from the significant rise in total protein, oligo and polysaccharide fractions, free amino acids, lipid and cholesterol contents compared to the significantly low values of DA‐treated group and control crabs. The present study clearly demonstrated the antagonistic effects of 5‐HT and DA on ovarian maturation in T. schirnerae. In conclusion, the stimulatory neurotransmitter, 5‐HT provides a non‐surgical practical solution for inducing ovarian growth and maturation in species of aquaculture importance.

HEMATO-BIOCHEMICAL PROFILING OF A BURROWING CRAB EXPOSED TO POLYSTYRENE MICROPLASTIC CONTAMINANT

The study evaluated the effect of polystyrene microplastic contaminant on hemato-biochemical parameters of Cardiosoma guanhumi from the mangrove area of Lagos Lagoon using standard methods. Total Haemocyte Count (THC) ranged between 3050.00±0.00 mL and 4200.00 ±0.05 mL with control crabs having the highest value of 4200.00±0.05 mL. There was significant difference between the treatment groups and the control (p&lt;0.05). Hemocyte sub-population variables showed that crabs fed the control and 0.01g polystyrene microplastic diets had higher granulocyte and monocyte populations but a decrease in agranulocytes. The crabs fed with the polystyrene microplastic contaminated diets were significantly higher in serum protein (32.50±0.05-32.90±0.10 gL-1) than the crab fed with control diet (20.09±0.05 gL-1). Crabs fed 0.01g and 0.02g polystyrene microplastic based diets recorded the same aspartate aminotransferase mean value (19.30 µI-1) which was significantly higher than the mean value (11.50 µI-1) recorded in crabs fed control diet. Crab fed 0.01g polystyrene microplastic based diet recorded most of the highest values for biochemical parameters: Alanine aminotransferase (13.00±0.05 µI-1), alkaline phosphatase (113.70±0.10 µI-1), lactate dehydrogenase (148.60±0.05 µI-1) and urea (40.41 ±0.15 µI-1). The changes in the crabs’ hematological and serum biochemical profiles in this study provide reliable and discriminatory data on the effect of microplastic contaminant calling for long-term monitoring to assess the eco-health of the mangrove system.