Lead Inhibits Postecdysial Exoskeletal Calcification in the Blue Crab (Callinectes sapidus)

Microplastics weaken the exoskeletal mechanical properties of Pacific whiteleg shrimp Litopenaeus vannamei

The ubiquitous presence of microplastics (MPs) in aquatic environments poses a significant threat to crustaceans. Although exoskeleton quality is critical for crustacean survival, the impact of MPs on crustacean exoskeletons remains elusive. Our study represents a pioneering effort to characterize the effects of MPs exposure on crustacean exoskeletons. In this study, the mechanical properties of whiteleg shrimp Litopenaeus vannamei exoskeletons were analyzed after exposure to environmentally realistic levels of MPs. Nanoindentation data demonstrated that MPs exposure significantly increased the hardness and modulus of both the carapace and abdominal segments of L. vannamei. Moreover, fractures and embedded MPs were detected on the exoskeleton surface using SEM-EDS analysis. Further analysis demonstrated that the degree of chitin acetylation (DA) in the shrimp exoskeleton, as indicated by FTIR peaks, was reduced by MPs exposure. In addition, exposure to MPs significantly inhibited the muscle Ca2+-ATPase activity and hemolymph calcium levels. Transcriptome and metabolome analyses revealed that the expression levels of genes encoding key enzymes and metabolites in the chitin biosynthetic pathway were significantly affected by MPs exposure. In conclusion, MPs at environmentally relevant concentrations may affect the exoskeletal mechanical properties of L. vannamei through a comprehensive mechanism involving the disruption of the crystalline structure of chitin, assimilation into the exoskeleton, and dysregulation of exoskeleton biosynthesis-related pathways.

Zinc is incorporated into the exoskeleton during post-ecdysial mineralization and inhibits exoskeletal calcification in the blue crab, Callinectes sapidus

Zinc is an essential but toxic metal with both natural and anthropogenic sources. Zinc has been reported to be present in crustacean exoskeleton, but it has remained unknown as to when zinc is incorporated into the shell during the molting cycle and the effects zinc has on exoskeleton properties. This study was conducted to identify a period during the molting cycle, in which zinc is incorporated into the exoskeleton of the blue crab, Callinectes sapidus, and to identify deleterious effects of zinc incorporation on the exoskeleton. It was hypothesized that zinc would be incorporated into the shell during the mineralization phase using calcium transporters, which would inhibit exoskeletal calcification. Post-ecdysial blue crabs were given two injections of zinc in the form of zinc chloride dissolved in Pantin's crustacean saline at the arthrodial membrane at three treatment levels: 0.0, 1.0 and 5.0 µg Zn/g wet weight. Exoskeletal and hemolymph samples were then analyzed for zinc, calcium, and magnesium content. Gill, muscle, and hepatopancreas samples were analyzed for zinc only. Epidermis samples were analyzed for carbonic anhydrase activity. The results showed that the injection dose of 1.0 µg Zn/g wet weight resulted in significant accumulation of zinc in the exoskeleton. There was no significant accumulation of exoskeletal zinc following 5.0 µg Zn/g wet weight injections. A significant reduction in exoskeletal calcium content in crabs treated with 1.0 or 5.0 µg Zn/g wet weight was also observed. The hypothetical model explaining zinc's incorporation into the exoskeleton and inhibition of exoskeletal calcification is proposed. Additionally, for the soft tissues examined, significant zinc accumulation was only observed in the hepatopancreas following zinc treatment. Our data points to the existence of crustacean zinc transporter. This study is the first to present evidence that zinc is deposited to the exoskeleton during post-ecdysial mineralization and inhibits exoskeletal calcification in a crustacean.

Heavy metals (HMs) pollution in the aquatic environment: Role of probiotics and gut microbiota in HMs remediation

The presence of heavy metals (HMs) in aquatic ecosystems is a universal concern due to their tendency to accumulate in aquatic organisms. HMs accumulation has been found to cause toxic effects in aquatic organisms. The common HMs-induced toxicities are growth inhibition, reduced survival, oxidative stress, tissue damage, respiratory problems, and gut microbial dysbiosis. The application of dietary probiotics has been evolving as a potential approach to bind and remove HMs from the gut, which is called "Gut remediation". The toxic effects of HMs in fish, mice, and humans with the potential of probiotics in removing HMs have been discussed previously. However, the toxic effects of HMs and protective strategies of probiotics on the organisms of each trophic level have not been comprehensively reviewed yet. Thus, this review summarizes the toxic effects caused by HMs in the organisms (at each trophic level) of the aquatic food chain, with a special reference to gut microbiota. The potential of bacterial probiotics in toxicity alleviation and their protective strategies to prevent toxicities caused by HMs in them are also explained. The dietary probiotics are capable of removing HMs (50-90%) primarily from the gut of the organisms. Specifically, probiotics have been reported to reduce the absorption of HMs in the intestinal tract via the enhancement of intestinal HM sequestration, detoxification of HMs, changing the expression of metal transporter proteins, and maintaining the gut barrier function. The probiotic is recommended as a novel strategy to minimize aquaculture HMs toxicity and safe human health.

Pollution and Potential Ecological Risk Evaluation Associated with Toxic Metals in an Impacted Mangrove Swamp in Niger Delta, Nigeria

Anthropogenic activities along coastal areas have contributed to the unwarranted discharge of toxic metals into mangrove swamps, posing risks to marine deposits and ecological environments. In this research, we studied the Isaka−Bundu tidal swamp area in the Niger Delta, which is an impacted mangrove creek located along the Bonny river, exposed to pollution pressures. The ecological risks (Er) of toxic metals in the sediments and water of the Isaka−Bundu tidal mangrove swamp followed a decreasing order (Cu > Zn > Cd > Cu > Pb > As), according to our results, while the potential ecological risk index (PERI) of the toxic metals in the sediments and water of the Isaka−Bundu tidal mangrove swamp can be said to have a very high ecological risk (PERI ≥ 600). The sediment pollution load index (PLI) was higher than 1 in all three analyzed stations, suggesting extremely toxic pollution. The enrichment evaluation shows that the studied stations have a moderate potential ecological risk of Cd, with the enrichment value for Pb showing low potential ecological risk. Our study shows that the Isaka−Bundu tidal mangrove swamp has a significant level of toxic metal pollution, which is evidence of the illegal activities performed in the Niger Delta.

How Does Carbon Dioxide-Induced Acidification Affect Postecdysial Exoskeletal Mineralization in the Blue Crab (Callinectes sapidus)?

Carbon dioxide (CO₂ ) enrichment in seawater because of increased use of fossil fuels can possibly cause detrimental effects on the physiological processes of marine life, especially shell builders, due to CO₂ -induced ocean acidification. We investigated, for the first time, specifically the effect of CO₂ enrichment on postecdysial shell mineralization in Crustacea using the blue crab, Callinectes sapidus, as the model crustacean. It was hypothesized that CO₂ enrichment of seawater would adversely affect exoskeletal mineralization in the blue crab. We used two groups of postecdysial crabs, with one group exposed to seawater at a pH of 8.20 and the other group treated with CO₂ -acidified seawater with a pH of 7.80-7.90. After a period of 7 days, samples of exoskeleton and hemolymph were collected from the survivors. Enrichment was found to significantly increase exoskeletal magnesium content by 104% relative to control, whereas a statistically nonsignificant elevation of 31% in exoskeletal calcium was registered. Because CO₂ treatment did not change the content of magnesium and calcium in the hemolymph, we postulate that increased exoskeletal mineralization in postecdysial blue crabs must stem from an increased influx of bicarbonate ions from the medium through the gill, to the hemolymph, and across the epidermis. In addition, the observed significant increase in the mass of exoskeleton following CO₂ treatment must be at least partly accounted for by enhanced postmolt carbonate salt deposition to the shell. Environ Toxicol Chem 2022;41:2950-2954. © 2022 SETAC.