Effects of ocean acidification and polystyrene microplastics on the oysters Crassostrea gigas: An integrated biomarker and metabolomic approach.

The adverse impacts of microplastics (MPs) or ocean acidification (OA) on mollusks have been widely reported, however, little is known about their combined effects on mollusks. The oysters Crassostrea gigas were exposed to two sizes of polystyrene MPs with 1 × 104 particles/L (small polystyrene MPs (SPS-MPs): 6 µm, large polystyrene MPs (LPS-MPs): 50-60 µm) at two pH levels (7.7 and 8.1) for 14 days. The antagonistic effects between MPs and OA on oysters were mainly observed. Single SPS-MPs exposure can induce CAT enzyme activity and LPO level in gills, while LPS-MPs exposure alone can increase PGK and PEPCK gene expression in digestive glands. Ocean acidification can increase clearance rate and inhibit antioxidant enzyme activity, whereas combined exposure of OA and SPS-MPs can affect the metabolomic profile of digestive glands. This study emphasized that the potential toxic effects of MPs under the scene of climate change should be concerned.

Combined effects of salinity and polystyrene microplastics exposure on the Pacific oysters Crassostrea gigas: Oxidative stress and energy metabolism.

Microplastics (MPs) pollution and salinity variation are two environmental stressors, but their combined effects on marine mollusks are rarely known. Oysters (Crassostrea gigas) were exposed to 1 × 104 particles L-1 spherical polystyrene MPs (PS-MPs) of different sizes (small polystyrene MPs (SPS-MPs): 6 µm, large polystyrene MPs (LPS-MPs): 50-60 µm) under three salinity levels (21, 26, and 31 psu) for 14 days. Results demonstrated that low salinity reduced PS-MPs uptake in oysters. Antagonistic interactions between PS-MPs and low salinity mainly occurred, and partial synergistic effects were mainly induced by SPS-MPs. SPS-MPs induced higher lipid peroxidation (LPO) levels than LPS-MPs. In digestive glands, low salinity decreased LPO levels and glycometabolism-related gene expression, which was related to salinity levels. Low salinity instead of MPs mainly affected metabolomics profiles of gills through energy metabolism and osmotic adjustment pathway. In conclusion, oysters can adapt to combined stressors through energy and antioxidative regulation.

Seasonal change of microplastics uptake in the Pacific oysters Crassostrea gigas cultured in the Yellow Sea and Bohai Sea, China.

This study investigated seasonal microplastics (MPs) pollution characteristics in oysters and surrounding surface seawater from five aquaculture farms located at the Yellow Sea and Bohai Sea. MPs abundances in oysters were 2.40 ± 0.14 (winter) to 3.28 ± 0.19 (autumn) items/individual, and 0.22 ± 0.02 (spring) to 0.45 ± 0.06 (summer) items/g (ww). In surface seawater, average seasonal MPs abundances were 3.41 ± 1.06-8.86 ± 2.48 items/L. Fibers were dominant shape, and cellophane and polyethylene terephthalate (PET) were dominant polymers in oysters and surface seawater. Positive correlation was found between oysters' MPs abundance (items/individual) and environmental factors (NO2-N (r = 0.466), and temperature (r = 0.485)) by Spearman correlation analysis in four seasons. Main environmental factor affecting seasonal MPs abundance of oysters and surface seawater was NH3-N and SiO3-Si in summer and winter respectively. In conclusion, seasonal change of MPs uptake in cultured oysters was relatively small.

Identification of a dopamine receptor in Sinonovacula constricta and its antioxidant responses.

The dopamine (DA) D2 receptor is a member of the G protein-coupled receptors of organisms and plays an important role in immune system regulation. The presence of DA receptors has been widely reported in vertebrates, but few studies have been conducted in shellfish. Here, we identified a novel DA-D2 receptor gene, ScDopR2-1, in the razor clam Sinonovacula constricta. ScDopR2-1 belongs to the family of G protein-coupled receptors, containing seven hydrophobic transmembrane domains, along with 16 predicted N-glycosylation sites and 69 phosphorylation sites. A longer third intracellular loop and a shorter C-terminus in ScDopR2-1 are characteristic features of D2 receptors. ScDopR2-1 is widely expressed in tissues from adult clams, showing high expression in siphon and foot tissues. Furthermore, in response to Vibrio anguillarum challenge, ScDopR2-1 expression levels are significantly increased in liver tissue. Moreover, changes in the activities of catalase (CAT) and superoxide dismutase (SOD) also indicate that the organism causes an immune response. In summary, the results indicate that ScDopR2-1 plays a pivotal role in antioxidant responses in S. constricta.

Construction of the First High-Density Genetic Linkage Map and Analysis of Quantitative Trait Loci for Growth-Related Traits in Sinonovacula constricta.

The razor clam (Sinonovacula constricta) is an important aquaculture species, for which a high-density genetic linkage map would play an important role in marker-assisted selection (MAS). In this study, we constructed a high-density genetic map and detected quantitative trait loci (QTLs) for Sinonovacula constricta with an F1 cross population by using the specific locus amplified fragment sequencing (SLAF-seq) method. A total of 315,553 SLAF markers out of 467.71 Mreads were developed. The final linkage map was composed of 7516 SLAFs (156.60-fold in the parents and 20.80-fold in each F1 population on average). The total distance of the linkage map was 2383.85 cM, covering 19 linkage groups with an average inter-marker distance of 0.32 cM. The proportion of gaps less than 5.0 cM was on average 96.90%. A total of 16 suggestive QTLs for five growth-related traits (five QTLs for shell height, six QTLs for shell length, three QTLs for shell width, one QTL for total body weight, and one QTL for soft body weight) were identified. These QTLs were distributed on five linkage groups, and the regions showed overlapping on LG9 and LG13. In conclusion, the high-density genetic map and QTLs for S. constricta provide a valuable genetic resource and a basis for MAS.