Effects of ocean acidifi cation driven by elevated CO_2 on larval shell growth and abnormal rates of the venerid clam, Mactra veneriformis

A bstract The venerid clam(M actra veneriformis Reeve 1854) is one of the main cultured bivalve species in intertidal and shallow subtidal ecosystems along the west coast of Korea. To understand the effects of ocean acidifi cation on the early life stages of Korean clams, we investigated shell growth and abnormality rates and types in the D-shaped, umbonate veliger, and pediveliger stages of the venerid clam M. veneriformis during exposure to elevated seawater pCO_2. In particular, we examined abnormal types of larval shell morphology categorized as shell deformations, shell distortions, and shell fi ssures. Specimens were incubated in seawater equilibrated with bubbled CO_2-enriched air at(400±25)×10^(-6)(ambient control),(800±25)×10^(-6)(high pCO_2), or(1 200±28)×10^(-6)(extremely high pCO_2), the atmospheric CO_2 concentrations predicted for the years 2014, 2084, and 2154(70-year intervals; two human generations), respectively, in the Representative Concentration Pathway(RCP) 8.5 scenario. The mean shell lengths of larvae were signifi cantly decreased in the high and extremely high pCO_2 groups compared with the ambient control groups. Furthermore, under high and extremely high pCO_2 conditions, the cultures exhibited signifi cantly increased abundances of abnormal larvae and increased severity of abnormalities compared with the ambient control. In the umbonate veliger stage of the experimental larvae, the most common abnormalities were shell deformations, distortions, and fi ssures; on the other hand, convex hinges and mantle protuberances were absent. These results suggest that elevated CO_2 exerts an additional burden on the health of M. veneriformis larvae by impairing early development.

Transcriptome profiling analysis of Mactra veneriformis by deepsequencing after exposure to 2,2′,4,4′-tetrabromodipheny1 ether

Polybrominated diphenyl ethers(PBDEs) are ubiquitous global pollutants, which are known to have immune, development, reproduction, and endocrine toxicity in aquatic organisms, including bivalves. 2,2′,4,4′-Tetrabromodiphenyl ether(BDE-47) is the predominant PBDE congener detected in environmental samples and the tissues of organisms. However, the mechanism of its toxicity remains unclear. In this study, high-throughput sequencing was performed using the clam Mactra veneriformis, a good model for toxicological research, to clarify the transcriptomic response to BDE-47 and the mechanism responsible for the toxicity of BDE-47. The clams were exposed to 5 μg/L BDE-47 for 3 days and the digestive glands were sampled for high-throughput sequencing analysis. We obtained 127 648, 154 225, and 124 985 unigenes by de novo assembly of the control group reads(CG), BDE-47 group reads(BDEG), and control and BDE-47 reads(CG & BDEG), respectively. We annotated 32 176 unigenes from the CG & BDEG reads using the NR database. We categorized 24 401 unigenes into 25 functional COG clusters and 21 749 unigenes were assigned to 259 KEGG pathways. Moreover, 17 625 diff erentially expressed genes(DEGs) were detected, with 10 028 upregulated DEGs and 7 597 downregulated DEGs. Functional enrichment analysis showed that the DEGs were involved with detoxification, antioxidant defense, immune response, apoptosis, and other functions. The m RNA expression levels of 26 DEGs were verified by quantitative real-time PCR, which demonstrated the high agreement between the two methods. These results provide a good basis for future research using the M. veneriformis model into the mechanism of PBDEs toxicity and molecular biomarkers for BDE-47 pollution. The regulation and interaction of the DEGs would be studied in the future for clarifying the mechanism of PBDEs toxicity.

Anti-hyperglycemic effect of the polysaccharide fraction isolated from mactra veneriformis

Total macromolecule extract was obtained from the soft body of Mactra veneriformis by the coupling techniques of decoction and alcohol precipitation.The extract was deproteinized with an ion exchange column,and resulted in the purifying of the crude polysaccharide fraction.It was found by chemical analysis that the crude polysaccharide part is composed of abundant polysacchar-ides(>95%)and few proteins(<1%).Furthermore,only one type of monosaccharide,glucose,was detected from its hydrolytes by thin-layer chromatography,indicating that the polysaccharides might be analogs of glucosan.The anti-hyperglycemia effects of the crude polysaccharide part were preliminarily investigated using several pharmacolo-gical methods in normal and diabetic mice.Animal experimental results showed that the crude polysaccharide fraction exhibited proper glycemia inhibition activity,and 300 mg/kg-weight dose has the optimal effect among all the studied doses.It is concluded that the crude polysaccharide fraction can be explored as a novel health product that possesses potential as an anti-hyperglycemic agent.