Crab Charybdis Japonica Research Articles

Behavioral Characteristics and Related Physiological and Ecological Indexes of Cultured Scallops (Mizuhopecten yessoensis) in Response to Predation by the Crab Charybdis japonica

To investigate the effects of predation by the paddle crab Charybdis japonica on the culture and survival of scallops (Mizuhopecten yessoensis) during bottom culture, we investigated the behavioral characteristics of three sizes (small, medium, and large) of scallops in response to exposure to crabs. We found that scallops escaped from crab predation by continuous shell closure or movement. Shell closure force increased with scallop size, and scallops of the same size that were stimulated by the presence of crabs closed their shell more frequently than control scallops. We also measured the activities of superoxide dismutase, catalase, arginine kinase, and octopine dehydrogenase in the gill, adductor muscle, and mantle of scallops before and after exposure to predation. Tissues that showed significant differences between control and test specimens were selected for deep sequencing of the transcriptome to identify and validate the key genes that were sensitive to predation. We found that when M. yessoensis is stimulated by the presence of predators, its behavioral characteristics and related physiological and ecological indexes undergo significant changes. The results are relevant for developing specifications for M. yessoensis seedling casting during bottom culture.

Development of a real-time PCR (qPCR) method for the identification of the invasive paddle crab Charybdis japonica (Crustacea, Portunidae).

Crabs can be transported beyond their native range via anthropogenic-mediated means such as aquarium trade, live seafood trade and shipping. Once introduced into new locations, they can establish persisting populations and become invasive, often leading to negative impacts on the recipient environment and native species. Molecular techniques are increasingly being used as complementary tools in biosecurity surveillance and monitoring plans for invasive species. Molecular tools can be particularly useful for early detection, rapid identification and discrimination of closely related species, including when diagnostic morphological characters are absent or challenging, such as early life stages, or when only part of the animal is available. In this study, we developed a species-specific qPCR assay, which targets the cytochrome c oxidase subunit 1 (CO1) region of the Asian paddle crab Charybdis japonica. In Australia, as well as many parts of the world, this species is considered invasive and routine biosecurity surveillance is conducted to reduce the risk of establishment. Through rigorous testing of tissue from target and non-target species we demonstrate that this assay is sensitive enough to detect as little as two copies per reaction and does not cross amplify with other closely related species. Field samples and environmental samples spiked with C. japonica DNA in high and low concentrations indicate that this assay is also a promising tool for detecting trace amounts of C. japonica eDNA in complex substrates, making it a useful complementary tool in marine biosecurity assessments.

Effects of habitat usage on hypoxia avoidance behavior and exposure in reef-dependent marine coastal species

Reef habitat in coastal ecosystems is increasingly being augmented with artificial reefs (ARs) and is simultaneously experiencing increasing hypoxia due to eutrophication and climate change. Relatively little is known about the effects of hypoxia on organisms that use complex habitat arrangements and how the presence of highly preferred AR habitat can affect the exposure of organisms to low dissolved oxygen (DO). We performed two laboratory experiments that used video recording of behavioral movement to explore 1) habitat usage and staying duration of individuals continuously exposed to 3, 5, and 7 mg/L dissolved oxygen (DO) in a complex of multiple preferred and avoided habitat types, and 2) the impact of ARs on exposure to different DO concentrations under a series of two-way replicated choice experiments with or without AR placement on the low-oxygen side. Six common reef-dependent species found in the northeastern sea areas of China were used (i.e., rockfish Sebastes schlegelii and Hexagrammos otakii, filefish Thamnaconus modestus, flatfish Pseudopleuronectes yokohamae, sea cucumber Stichopus japonicus, and crab Charybdis japonica). Results showed that lower DO levels decreased the usage of preferred habitats of the sea cucumber and the habitat-generalist filefish but increased the habitat affinity to preferred habitat types for the two habitat-specific rockfishes. Low DO had no effect on the crab’s habitat usage. In the choice experiment, all three fish species avoided 1 mg/L, and the rockfish S. schlegelii continued to avoid the lower DO when given choices involving pairs of 3, 5, and 7 mg/L, while H. otakii and the flatfish showed less avoidance. The availability of ARs affected exposure to low DO for the habitat-preferring rockfishes but was not significant for the flatfish. This study provides information for assessing the ecological effects and potential for adaptation through behavioral movement for key reef-dependent species under the increasing overlap of ARs and hypoxia anticipated in the future.

Predator Presence Alters Intestinal Microbiota in Mussel.

Intestinal microbes are essential participants in host vital activities. The composition of the microbiota is closely related to the environmental factors. Predator presence may impact on intestinal microbiota of prey. In the present study, stone crab Charybdis japonica was used as potential predator, an external stress on mussel Mytilus coruscus, to investigate the intestinal microbiota alteration in M. coruscus. We set up two forms of predator presence including free crab and trapped crab, with a blank treatment without crab. The composition of intestinal microbiota in mussels among different treatments showed significant differences by 16S rRNA techniques. The biodiversity increased with trapped crab presence, but decreased with free crab presence. Neisseria, the most abundant genus, fell with the presence of crabs. Besides, the Arcobacter, a kind of pathogenic bacteria, increased with free crab presence. Regarding PICRUTs analysis, Environmental Information Processing, Genetic Information Processing and Metabolism showed differences in crab presence treatments compared with the blank, with a bit higher in the presence of free crab than trapped crab. In conclusion, trapped crab effects activated the metabolism and immunity of the intestinal flora, but free crabs made mussels more susceptible to disease and mortality, corresponding to the decreased biodiversity and the increased Arcobacter in their intestine.

Terrestrial runoff influences the transport and contamination levels of Toxoplasma gondii in marine organisms

There is a growing concern regarding the potential adverse impact of Toxoplasma gondii contamination of the marine environment on marine wildlife and public health. Terrestrial runoff is a significant route for dissemination of T. gondii oocysts from land to sea. Yet, the influence of terrestrial runoff on T. gondii prevalence in marine animals in China is largely unknown. To address this concern, we examined the presence of T. gondii in marine oysters Crassostrea spp., rockfish Sebastes schlegelii (S. schlegelii), fat greenling fish Hexagrammos otakii (H. otakii), and Asian paddle crab Charybdis japonica (C. japonica) using a PCR assay targeting T. gondii B1 gene. A total of 1920 samples were randomly collected, in Jan-Dec 2020, from terrestrial runoff areas (TRA, TRB, and TRC) and non-terrestrial runoff area (Grape bay) in Weihai, China. T. gondii prevalence in TRB and TRC was 6.04 % and 5.83 %, respectively, which was higher than 2.29 % detected in the non-terrestrial runoff area. The highest prevalence was detected in Crassostrea spp., and a correlation was observed between T. gondii prevalence and weight of Crassostrea spp. The temperature, but not precipitation, significantly correlated with T. gondii prevalence. Understanding the fate of T. gondii delivered to oceans by terrestrial runoff is critical for predicting future disease risks for marine wildlife and humans.

Effects of berberine hydrochloride on immune response in the crab Charybdis japonica

Berberine hydrochloride is the main effective component of Coptis spp. used in Chinese herbal medicine and its underlying molecular mechanisms, responsible for inducing effects in crustacean species, are not fully understood. In this study, the molecular response of the crab Charybdis japonica to berberine hydrochloride exposure was studied using transcriptome sequencing. The survival rate, gene expression and activities of several immune enzymes were measured after berberine hydrochloride treatments, with or without injection of the pathogenic bacterium Aeromonas hydrophila. A total of 962 differentially expressed genes (464 up-regulated and 498 down-regulated) were observed during exposure to 100 mg/L of berberine hydrochloride and in the control group after 48 h. Enrichment analysis revealed that these genes are involved in metabolism, cellular processes, signal transduction and immune functions, indicating that exposure to berberine hydrochloride activated the immune complement system. This bioactive compound simultaneously activated fibrinogen beta (FGB), fibrinogen alpha (FGA), alpha-2-macroglobulin (A2M), kininogen (KNG), fibrinogen gamma chain (FGB), alpha-2-HS-glycoprotein (AHSG), caspase-8 (CASP8), cathepsin L (CTSL), adenylate cyclase 3 (Adcy3) and MMP1. Its action could significantly increase the survival rate of the crabs injected with A. hydrophila and promote the activity of LZM, Caspas8, FGA, ACP and AKP in the hepatopancreas. When A. hydrophila was added, the neutralization of 300 mg/L berberine hydrochloride maximized the activities of Caspas8, LZM, ACP and AKP. Our results provide a new understanding of the potential effects of berberine hydrochloride on the immune system mechanisms in crustaceans.

Exceptional properties of hyper-resistant armor of a hydrothermal vent crab

Animals living in extreme environments, such as hydrothermal vents, would be expected to have evolved protective shells or exoskeletons to maintain homeostasis. The outer part of the exoskeleton of vent crabs (Austinograea sp.) in the Indian Ocean hydrothermal vent was one of the hardest (approximately 7 GPa) biological materials ever reported. To explore the exoskeletal characteristics of vent crabs which enable them to adapt to severe environments, a comparative analysis was conducted with the Asian paddle crab (Charybdis japonica) living in coastal areas. Nanoindentation, thermogravimetric analysis, scanning electron microscopy, energy dispersive x-ray analysis, and Raman spectroscopy were used to analyze the mechanical properties, thermal stability, structure, surface components, and the composition of compounds, respectively. Though both species have four-layered exoskeletons, the outermost layer of the vent crab, a nano-granular structure, was much thicker than that of the coastal crab. The proportions of aluminum and sulfur that constitute the epicuticle of the exoskeleton were higher in the vent crab than in the coastal crab. There was a lack of water or volatile substances, lots of CaCO3, and no carotenoid-based compounds in the exoskeleton of the vent crab. These might have improved the mechanical properties and thermal stability of the hydrothermal species.

Range expansion of the invasive portunid crab Charybdis japonica in New Zealand

ABSTRACT Charybdis japonica, a large invasive portunid, has been recorded in New Zealand since its detection in the Waitematā Harbour in 2000. In this study, the distribution, invasion history, abundance and population structure were investigated for C. japonica across the North Island of New Zealand. This was done using various distribution data available, trapping across several sites and interviews with commercial fishermen. Charybdis japonica was detected in the previously uninvaded Tauranga, Ohiwa, Hokianga, Manukau Harbours and Great Barrier Island. The rate of spread for C. japonica is continuous, with harbours or estuaries hundreds of kilometres apart having detections every two to three years. Population abundances reported by commercial fishermen constantly increased, with no signs of stabilisation or decrease. Catches were male-biased, with female abundance varying seasonally. Several possible pathways and vectors may be responsible for this spread, including shipping and aquaculture, on top of dispersal of larvae by currents across the North Island. Further research is required to determine population sources, with findings providing important information for invasive species monitoring and management.

Effects of the swimming crab Charybdis japonica on sea urchin Mesocentrotus nudus grazing: cage experiments in barren ground and land-based tanks

Effects of the swimming crab Charybdis japonica on sea urchin Mesocentrotus nudus grazing: cage experiments in barren ground and land-based tanks

Nano-ZnO impairs anti-predation capacity of marine mussels under seawater acidification.

Artificial nanoparticles and ocean acidification (OA) caused by the rapid increase of CO2 absorbed by the ocean are both ecologically hazardous to marine organisms. The combined effects of the two environmental stressors on the anti-predation ability of marine mussels were studied. Mytilus coruscus was exposed to three different gradient concentrations of nano-ZnO (0, 2.5, 10 mg/L) in combination of two pH levels (7.7 and 8.1). The crab Charybdis japonica was used as its predator. During the experiment, anti-predator indexes, including number of byssus threads (NBT), shell-closing strength (SCS), diameter of byssus thread (BTD), length of byssus thread (BTL), cumulative length of byssus thread (CBTL) and cumulative volume of byssus thread (CBTV) were studied. The results showed that predator induced the anti-predation responses in M. coruscus, and NBT, SCS, BTL, CBTL and CBTV were significantly increased. Under the conditions of pH 7.7 and 10 mg/L nano-ZnO, NBT, SCS, BTD, BTL, CBTL, and CBTV were significantly reduced. What's more, significant interactions among pH, nano-ZnO and predator were observed in CBTL and CBTV. Therefore, the joint treatment of nano-ZnO and low pH reduces the adhesion strength of byssus thread and may increase the probability of mussels being preyed.

Growth and reproductive ecology of the portunid crab Charybdis japonica in an open seacoast and an inland bay in Fukuoka, Japan

Growth and reproductive ecology of the portunid crab Charybdis japonica in an open seacoast and an inland bay in Fukuoka, Japan

Classification of Hemocytes from Four Crustaceans and Cross-Reactivity of Their Antisera

Common antigens and analyzed the hemocytes of the lady crab (Charybdis japonica) were studied. Chinese mitten crab (Eriocheir sinensis), Dungeness crab (Cancer magister), and red king crab (Paralithodes camtschaticus) using a laser scanning confocal microscope (LSCM), flow cytometry (FCM), Western blotting (WB), and transmission electron microscopy. In this paper analyzed hemocyte classification and immunological characteristics of the whole proteins in these species and their antisera. Four antisera positively cross-reacted, to varying degrees, with hemocytes of the four species. Two subpopulations were classified in C. japonica, P. camtschaticus, and E. sinensis and three in C. magister. The LSCM results showed that four antisera were positive with the hemocytes of the four crustacean species, respectively. Dot fluorescent signals on the hemocyte membranes show a cricoid intensive distribution. FCM analysis showed a positive rate of cross-reaction, in which the reaction of the antisera with its own hemocytes was higher than that with other species' hemocytes. The positive rate of granulocytes was always higher than that of hyalinocytes. Western blotting results showed that the four antisera mainly recognized antigens with molecular weights of about 75 or 80 kDa in the hemocytes of C. japonica, 80 or 90 kDa in the hemocytes of P. camtschaticus, 30 and 82 kDa in the hemocytes of E. sinensis, and 43 or 70 kDa in the hemocytes of C. magister. More lanes reacted between hemocytes of E. sinensis and C. magister and their antisera. The results indicate antigenic similarities among the hemocytes of the four crustacean species.

Mitochondrial prohibitin and its ubiquitination during spermatogenesis of the swimming crab Charybdis japonica

It has been proposed that prohibitin (PHB) involved in multiple cellular functions, including cell proliferation, differentiation, apoptosis, senescence and carcinogenesis. Various cellular compartment location of PHB demonstrates its diverse roles. Based on the full-length sequence of PHB gene, we analyzed the deduced amino acid sequence and the predicted protein structure of this gene in the swimming crab Charybdis japonica. It shows that the structure and function of PHB are conservative. The expression level of PHB mRNA and protein in different tissues were analyzed by sqRT-PCR and western blot respectively, which showed its high expression in testis. We then traced PHB protein by immunofluorescence, and we found its diverse distribution in cytoplasm and mitochondria at different stages. We propose that PHB may participate actively in spermatogenic cell anti-apoptosis, cell nucleus distortion as well as acrosome morphogenesis during the spermatogenesis in Charybdis japonica. Furthermore, PHB was found to be ubiquitinated at different levels. Its signal was weak in spermatocytes and Stage 1 spermatids, stronger in stage 2–4 spermatids, and lowest in mature sperm. Our data shows that PHB may mediate the paternal mitochondrial material degradation by ubiquitination. We conclude that PHB is indispensable in the spermatogenesis of the swimming crab Charybdis japonica through different testis developmental stages.

Effects of seawater pH and temperature on foraging behavior of the Japanese stone crab Charybdis japonica

We examined prey selection and foraging behaviors of the crab Charybdis japonica exposed to four combinations of pH (7.3 and 8.1) and temperature (18°C and 25°C). The order of prey selection by C. japonica was Potamocorbula laevis, Ruditapes philippinarum, Tegillarca granosa and Mactra veneriformis. Under high pCO2, times for searching, breaking, eating and handling were all significantly longer than those at the normal pCO2, and the prey profitability and predation rate under high pCO2 were significantly lower than normal pCO2. Moreover, temperature significantly influenced the foraging behaviors, but its effects were not as strong as those of pH; times for searching, eating and handling under high temperature were significantly lower than the low temperature, and the prey predation rates under high temperature was significantly higher than low temperature. In conclusion, high pCO2 negatively affected the foraging behavior, but high temperature actively stimulated the foraging behaviors of crabs.

Molecular cloning and expression of the stress gene HSP70 in the marine crab Charybdis japonica (A. Milne-Edwards, 1861) (Decapoda: Brachyura: Portunidae) in response to ammonia-N, nitrite-N, and sulfide exposure

A full-length complementary DNA sequence of heat-shock protein 70 (HSP70) was cloned from the hepatopancreas of Charybdis japonica (A. Milne-Edwards, 1861) through reverse transcription-polymerase chain reaction and rapid amplification of cDNA ends. The expression profile of HSP70 in different tissues of C. japonica and its expression upon exposure to ammonia-N, nitrite-N, and sulfide was also investigated. The full-length cDNA of HSP70 was 2203 bp long and contained a 107 bp 5′ untranslated region (UTR), a 143 bp 3′ UTR, and a 1953 bp open reading frame, which distributed 108-2060 bp and encoded a polypeptide of 650 amino acids (aa) with a calculated molecular mass of 71.24 kDa and an isoelectric point of 5.34. Three signature sequences of the HSP70 family, IDLGTT-S-V (residues 9-18), IFDLGGGTFDVSIL (197-210 aa), and IVLVGGSTRIPKIQK (334-348 aa) were detected in the predicted amino-acid sequence. The HSP70 gene of C. japonica showed the highest similarity (>90%) to HSP70 from other crustacean species. The HSP70 gene was expressed in all tissues tested, and its abundance in these tissues can be arranged as hepatopancreas > stomach > gill > heart > ova > muscle. The expression of HSP70 was significantly induced after the stress of ammonia-N, nitrite-N, and sulfide, and the induced degree showed a positively correlation with increasing concentrations. The HSP70 expression reached a peak after 3 or 6 h of stress, which suggests that the HSP70 expression was affected quickly by the changes of environmental factors.

Effect of an escape vent in accordion-shaped traps on the catch and size of Asian paddle crabs Charybdis japonica in an artificial reef area

Accordion-shaped traps are widely used in China to catch the Asian paddle crab Charybdis japonica but traps of conventional design often catch juvenile crabs. A new type of accordion-shaped trap with an escape vent (L×W=4.3 cm×3.0 cm) was designed and a comparative study between the newly designed and conventional traps was performed in the artificial reef area of Zhuwang, Laizhou Bay, China from June to August 2012. The mean catch per unit effort (CPUE) of undersized crabs was significantly lower in the vented traps than in the conventional traps (paired t -test, n=30, P<0.001), while the CPUE of marketable crabs was significantly higher in the vented traps (paired t-test, n=30, P<0.001). The mean size of crabs (carapace length) caught in the vented traps was significantly larger than in conventional traps (paired t-test, n=29, P<0.001). The ratio of undersized crabs was 35.05±2.57% in conventional traps and 12.53±0.69% in vented traps (significantly lower, paired t-test, n=29, P<0.001). Therefore, a 4.3 cm×3.0 cm escape vent was considered appropriate for C. japonica fishing in the artificial reef area. This finding will assist the development of more sustainable and efficient crab fishing methods using accordion-shaped traps.

Conflicting Effects of Predator Cue and Ocean Acidification on the MusselMytilus coruscusByssus Production

Understanding the impact of ocean acidification and warming on communities and ecosystems is a researcher priority. This can only be achieved through a combination of experimental and field approaches that would allow developing a mechanistic understanding of impacts across level of biological organizations. Surprisingly, most published studies are still focusing on single species responses with little consideration for interspecific interactions. In this study, the impacts of a 3 days exposure to three parameters (temperature, pH, and presence/absence of the predator cue of the crab Charybdis japonica) and their interactions on an ecologically important endpoint were evaluated: the byssus production of the mussel Mytilus coruscus. Tested temperatures (25°C and 30°C) were within the present range of natural variability whereas pH (8.1, 7.7, and 7.4) covered present as well as near-future natural variability. As expected, the presence of the crab cue induced an antipredator response in Mytilus coruscus (significant 10% increase in byssus secretion rate, 22% increase in frequency of shed byssus, and 30% longer byssus). Decreased pH but not temperature had a significant negative impact on the same endpoints (up to a 17% decrease in byssus secretion rate, 40% decrease in frequency of shed byssus, and 10% shorter byssus at pH 7.3 as compared with pH 8.1) with no significant interactions between the three tested parameters. In this study, it has been hypothesized that pH and predator cue have different modes of action and lead to conflicting functional responses (escape response versus stronger attachment). Functional consequences for ecosystem dynamics still need to be investigated.

Anti-predatory responses of the thick shell mussel Mytilus coruscus exposed to seawater acidification and hypoxia

Ocean acidification and hypoxia, both caused by anthropogenic activities, have showed deleterious impacts on marine animals. However, their combined effect on the mussel's defence to its predator has been poorly understood, which hinders us to understand the prey–predator interaction in marine environment. The thick shell mussel Mytilus coruscus and its predator, the Asian paddle crab Charybdis japonica were exposed to three pH levels (7.3, 7.7, 8.1) at two concentrations of dissolved oxygen (2.0 mg L−1, 6.0 mg L−1) seawater. The anti-predatory responses of mussels, in terms of byssus thread production were analyzed after 72 h exposure. During the experiment, frequency of shedding stalks (mussels shed their byssal stalks to release themselves from attachment and allow locomotion) and number of byssus threads increased with time, were significantly reduced by hypoxia and low pH levels, and some interactions among time, predator, DO and pH were observed. As expected, the presence of the crab induced an anti-predator response in M. coruscus (significant increases in most tested parameters except the byssus thread length). Acidification and hypoxia significantly reduced byssus thread diamter at the end of the experiment, but not the byssus thread length. Cumulative byssus thread length and volume were significantly impaired by hypoxia and acidification. Our results highlight the significance of anti-predatory responses for adult mussel M. coruscus even under a stressful environment in which stress occurs through ocean acidification and hypoxia. By decreasing the strength of byssus attachment, the chance of being dislodged and consumed by crabs is likely increased. Our data suggest that there are changes in byssus production induced by hypoxia and acidification, which may affect predation rates on M. coruscus in the field.

Characterize and Gene Expression of Heat Shock Protein 90 in Marine Crab Charybdis japonica following Bisphenol A and 4-Nonylphenol Exposures.

ObjectivesHeat shock protein 90 (HSP90) is a highly conserved molecular chaperone important in the maturation of a broad spectrum of protein. In this study, an HSP90 gene was isolated from Asian paddle crab, Charybdis japonica, as a bio-indicator to monitor the marine ecosystem.MethodsThis work reports the responses of C. japonica HSP90 mRNA expression to cellular stress by endocrine disrupting chemicals (EDCs), such as bisphenol A (BPA) and 4-nonylphenol (NP) using real-time. reverse transcription polymerase chain reaction.ResultsThe deduced amino acid sequence of HSP90 from C. japonica shared a high degree of homology with their homologues in other species. In a phylogenetic analysis, C. japonica HSP90 is evolutionally related with an ortholog of the other crustacean species. The expression of HSP90 gene was almost distributed in all the examined tissues of the C. japonica crab but expression levels varied among the different body parts of the crabs. We examined HSP90 mRNA expression pattern in C. japonica crabs exposed to EDCs for various exposure times. The expression of HSP90 transcripts was significantly increased in C. japonica crabs exposed to BPA and NP at different concentrations for 12, 24, 48 and 96 hours. The mRNA expression of HSP90 gene was significantly induced in a concentration- and time-dependent manner after BPA or NP exposures for 96 hours.ConclusionsTaken together, expression analysis of Asian paddle crab HSP90 gene provided useful molecular information about crab responses in stress conditions and potential ways to monitor the EDCs stressors in marine environments.

The targeting of large-sized benthic macrofauna by an invasive portunid predator: evidence from a caging study

The Portunid crab Charybdis japonica was first found in Waitemata Harbour, New Zealand, in 2000. It has established breeding populations and has been spreading, yet information on its dietary preferences in New Zealand are unknown. We conducted field caging experiments to elucidate prey choices and potential impacts of Charybdis on benthic communities. We tested the hypothesis that Charybdis would reduce the previously demonstrated positive influence of native pinnid bivalves, Atrina zelandica, on the abundance and richness of surrounding soft-sediment macrofauna. Adult male Charybdis were introduced to cages with and without Atrina that included soft-sediment macrofaunal communities of ambient composition and abundance. After leaving the crabs to feed overnight, changes in community structure (relative to sediments without crabs) were determined by coring the sediment and analysing the resident macrofauna. Prey choices were verified by extracting taxa from the stomachs of crabs collected from the cages in which they had been feeding. The abundance of large taxa including burrowing urchins, bivalves and native crabs was lower in the presence of Charybdis compared to areas without this invader. The stomach contents of Charybdis were dominated by these same three taxa, constituting 85 % of the prey abundance when using stomach fullness as a weighting factor. Our hypothesis was supported with the greatest net losses occurring in cages with Charybdis and Atrina. Reduction in the abundance of Echinocardium cordatum by Charybdis could have cascading ecological effects, as these urchins play a critical role in benthic soft-sediment ecosystems in New Zealand via bioturbation and biogenic disturbance.