Guangxu Liu

Ocean acidification increases cadmium accumulation in marine bivalves: a potential threat to seafood safety

To date, the effects of ocean acidification on toxic metals accumulation and the underlying molecular mechanism remains unknown in marine bivalve species. In the present study, the effects of the realistic future ocean pCO2 levels on the cadmium (Cd) accumulation in the gills, mantle and adductor muscles of three bivalve species, Mytilus edulis, Tegillarca granosa, and Meretrix meretrix, were investigated. The results obtained suggested that all species tested accumulated significantly higher Cd (p < 0.05) in the CO2 acidified seawater during the 30 days experiment and the health risk of Cd (based on the estimated target hazard quotients, THQ) via consumption of M. meretrix at pH 7.8 and 7.4 significantly increased 1.21 and 1.32 times respectively, suggesting a potential threat to seafood safety. The ocean acidification-induced increase in Cd accumulation may have occurred due to (i) the ocean acidification increased the concentration of Cd and the Cd2+/Ca2+ in the seawater, which in turn increased the Cd influx through Ca channel; (ii) the acidified seawater may have brought about epithelia damage, resulting in easier Cd penetration; and (iii) ocean acidification hampered Cd exclusion.

Toxicity of copper, lead, and cadmium on the motility of two marine microalgae Isochrysis galbana and Tetraselmis chui.

Computer assisted movement tracking was used to characterize the motility of two marine microalgae, Isochrysis galbana and Tetraselmis chui, and to investigate the toxicity of Cu, Pb, and Cd on motile percentage, curvilinear velocity, average path velocity, straight line velocity, linearity, straightness, and wobble. Except for motile percentage, all other motility parameters differed significantly between I. galbana and T. chui. Based on relative motile percentage data, the median effective concentration (EC50) of Cu on the motility of I. galbana and T. chui was 31.4 and 1.3 micromol/L, respectively, while for Pb it was 37.8 and 10.9 micromol/L and for Cd it was 121.6 and 37.8 micromol/L, respectively. Compared to I. galbana, T. chui was more sensitive to all tested metals. The toxic effect of the heavy metals on motility exhibited the following decreasing order for both species: Cu > Pb > Cd. Our results indicate that L. galbana and T. chui motility is sensitive to heavy metals and can be used as an indicator for toxicology bioassays.

Ocean acidification adversely influences metabolism, extracellular pH and calcification of an economically important marine bivalve, Tegillarca granosa

Oceanic uptake of CO2 from the atmosphere has significantly reduced surface seawater pH and altered the carbonate chemistry within, leading to global Ocean Acidification (OA). The blood clam, Tegillarca granosa, is an economically and ecologically significant marine bivalve that is widely distributed along the coastal and estuarine areas of Asia. To investigate the physiological responses to OA, blood clams were exposed to ambient and three reduced seawater pH levels (8.1, 7.8, 7.6 and 7.4) for 40 days, respectively. Results obtained suggest that OA suppresses the feeding activity and aerobic metabolism, but elevates proteins catabolism of blood clams. OA also causes extracellular acidosis and decreases haemolymph Ca2+ concentration. In addition, our data also suggest that OA impairs the calcification process and inner shell surface integrity. Overall, OA adversely influences metabolism, acid-base status and calcification of blood clams, subsequently leading to a decrease in the fitness of this marine bivalve species.

Benzo[a]pyrene exposure under future ocean acidification scenarios weakens the immune responses of blood clam, Tegillarca granosa

Abstract Persistent organic pollutants (POPs) are known to converge into the ocean and accumulate in the sediment, posing great threats to marine organisms such as the sessile bottom burrowing bivalves. However, the immune toxicity of POPs, such as B[a]P, under future ocean acidification scenarios remains poorly understood to date. Therefore, in the present study, the impacts of B[a]P exposure on the immune responses of a bivalve species, Tegillarca granosa, under present and future ocean acidification scenarios were investigated. Results obtained revealed an increased immune toxicity of B[a]P under future ocean acidification scenarios in terms of reduced THC, altered haemocyte composition, and hampered phagocytosis, which may attribute to the synergetic effects of B[a]P and ocean acidification. In addition, the gene expressions of pathogen pattern recognition receptors (TLR1, TLR2, TLR4, TLR6), pathway mediators (TRAF6, TAK1, TAB2, IKK&agr; and Myd88), and effectors (NF‐&kgr;B) of the important immune related pathways were significantly down‐regulated upon exposure to B[a]P under future ocean acidification scenarios. Results of the present study suggested an increased immune toxicity of B[a]P under future ocean acidification scenarios, which will significantly hamper the immune responses of T. granosa and subsequently render individuals more susceptible to pathogens challenges. Graphical abstract Figure. No Caption available. HighlightsIncreased immune toxicity of B[a]P under future ocean acidification scenarios.Synergetic effects of B[a]P and OA on THC, haemocyte composition, phagocytosis.B[a]P under future OA scenarios down‐regulated expression of immune related genes.

Effects of anthropogenic sound on digging behavior, metabolism, Ca(2+)/Mg(2+) ATPase activity, and metabolism-related gene expression of the bivalve Sinonovacula constricta.

Anthropogenic sound has increased significantly in the past decade. However, only a few studies to date have investigated its effects on marine bivalves, with little known about the underlying physiological and molecular mechanisms. In the present study, the effects of different types, frequencies, and intensities of anthropogenic sounds on the digging behavior of razor clams (Sinonovacula constricta) were investigated. The results showed that variations in sound intensity induced deeper digging. Furthermore, anthropogenic sound exposure led to an alteration in the O:N ratios and the expression of ten metabolism-related genes from the glycolysis, fatty acid biosynthesis, tryptophan metabolism, and Tricarboxylic Acid Cycle (TCA cycle) pathways. Expression of all genes under investigation was induced upon exposure to anthropogenic sound at ~80 dB re 1 μPa and repressed at ~100 dB re 1 μPa sound. In addition, the activity of Ca2+/Mg2+-ATPase in the feet tissues, which is directly related to muscular contraction and subsequently to digging behavior, was also found to be affected by anthropogenic sound intensity. The findings suggest that sound may be perceived by bivalves as changes in the water particle motion and lead to the subsequent reactions detected in razor clams.

Immunotoxicity of nanoparticle nTiO2 to a commercial marine bivalve species, Tegillarca granosa

Abstract The increasing production and extensive application of nanoparticles (NPs) inevitably leads to increased release of NPs into the marine environment and therefore poses a potential threat to marine organisms, especially the sessile benthic bivalves. However, the impacts of NPs on the immunity of commercial and ecological important bivalve species, Tegillarca granosa, still remain unknown to date. In addition, the molecular mechanism of the immunotoxicity of NPs still remains unclear in marine invertebrates. Therefore, the immunotoxicity of nTiO2 exposure to T. granosa at environmental realistic concentrations was investigated in the present study. Results obtained showed that the total number, phagocytic activity, and red granulocytes ratio of the haemocytes were significantly reduced after 30 days nTiO2 exposures at the concentrations of 10 and 100 &mgr;g/L. Furthermore, the expressions of genes encoding Pattern Recognition Receptors (PPRs) and downstream immune‐related molecules were significantly down‐regulated by nTiO2 exposures, indicating a reduced sensitivity to pathogen challenges. In conclusion, evident immunotoxicity of nTiO2 to T. granosa at environmental realistic concentrations was detected by the present study. In addition, the gene expression analysis suggests that the PRRs (both TLRs and RIG1 investigated) may be the molecules for NPs recognition in marine invertebrates. Graphical abstract Figure. No Caption available. HighlightsTiO2 NPs leads to a reduction in total haemocytes counts and phagocytosis.Blood cell type composition is altered after TiO2 NPs exposure.TiO2 NPs exposure down‐regulates immune‐related genes.TiO2 NPs weakens immune responses of blood clam.

Population Genetic Structure of the Blood Clam, Tegillarca granosa, Along the Pacific Coast of Asia: Isolation by Distance in the Sea

ABSTRACT The blood clam, Tegillarca granosa, is widely distributed along the coasts of the Indo-Pacific region, providing an excellent opportunity to study gene flow in sessile marine mollusks. In the present study, amplified fragment length polymorphism (AFLP) DNA markers were used to analyze the genetic structure of five blood clam populations. Genetic differentiation (Gst) and Neis genetic distances between population pairs were found to range from 0.0245 to 0.0785 and 0.0398 to 0.1125, respectively. An AMOVA analysis showed that 89.09% of the genetic variation occurred within populations and only 10.92% occurred among populations, indicating a high degree of genetic homogeneity, probably due to considerable gene flow (average Nm = 7.1853) among populations. Cluster analysis using the unweighted pair group method average (UPGMA) showed that geographically closer populations were clustered, suggesting isolation by distance, which was further supported by a significant positive correlation between Gst and logit transformed geographic distance through a Mantel test and reduced major axis regression (r = 0.77, p < 0.05). The evident isolation by distance observed among blood clam populations along the Pacific coast of Asia is likely to be a consequence of both the passive larval dispersal carried by the South China Sea Warm Current and the genetic homogeneity caused by aquaculture-associated human activities.

Effects of reduced pH and elevated pCO2 on sperm motility and fertilisation success in blood clam, Tegillarca granosa

ABSTRACT Although it has been shown that ocean acidification generally has a negative impact on fertilisation success of broadcast spawning marine organisms, whether induced fertilisation success reduction is a consequence of elevated pCO2 or decreased pH remains unclear. Therefore, the impacts of HCl- and CO2-induced acidified seawater on sperm motility and gametes fertilisation capability of a broadcast spawning bivalve species, Tegillarca granosa were investigated in the present study. The results showed that the fertilisation capability of both gametes was significantly reduced in either HCl- or CO2-acidified seawater. In addition, significant impacts on sperm motility were observed in the group exposed to CO2-acidified seawater, suggesting that this parameter is sensitive to pCO2 instead of solely pH value. The differences between the two seawater acidification manipulating methods may be due to the intrinsic difference in diffusion capability of CO2 and protons.

Waterborne Cd 2+ weakens the immune responses of blood clam through impacting Ca 2+ signaling and Ca 2+ related apoptosis pathways

ABSTRACT Exposure to heavy metals such as Cadmium (Cd) may exert detrimental impacts on the immune responses of marine bivalve species. However, the immunotoxicity of Cd on blood clams remains unknown to date. Furthermore, though Cd2+ is known to compete with calcium (Ca2+) ions for their binding sites in cells and inhibit Ca2+ influx, whether Cd2+ weakens the immune responses of marine bivalves through inducing intracellular Ca2+ disorders still remains unclear. Therefore, the immunotoxicity of Cd2+ at different waterborne Ca2+ concentrations on blood clam, Tegillarca granosa, were investigated in the present study. Results obtained demonstrated that the total number, phagocytic activity, and red granulocytes ratio of the haemocytes were all significantly reduced after 10 days exposure of individuals to 25 &mgr;g/L Cd2+. However, when the waterborne Ca2+ concentrations were elevated by 10% and 20% (approximately 370 and 410 mg/L, respectively), mitigation effects on the immune responses of individuals were detected. In addition, though the expressions of genes from the Ca2+ signaling and Ca2+‐related apoptosis pathways were significantly altered by Cd2+ exposure, the expression patterns of these genes were similar to that of the control when the waterborne Ca2+ concentrations were elevated, suggesting a relieving effect of waterborne Ca2+ on Cd2+ induced toxicity to haemocytes. The results obtained in the present study revealed that waterborne Cd2+ may hamper the immune responses of T. granosa through influencing Ca2+ signaling and Ca2+‐related apoptosis pathways, which can be partially mitigated by elevating the waterborne Ca2+ concentrations. HighlightsCd2+ exposure induced a reduction in total haemocytes counts and phagocytosis.Cd2+ exposure affected the expressions of genes from the Ca2+ signaling pathway.Cd2+ exposure influenced the Ca2+‐related apoptosis pathways.Elevated waterborne Ca2+ concentrations can relieve the immunotoxicity of Cd2+.

Ca2+-channel and calmodulin play crucial roles in the fast electrical polyspermy blocking of Tegillarca granosa (Bivalvia: Arcidae)

To address the problem of polyspermy during artificial breeding practices of commercial free-spawning marine bivalve species, a greater understanding of the mechanisms behind polyspermy blocking is required. Therefore, we investigated the roles of the calcium ion (Ca) channel and calmodulin (CaM) in fast electrical polyspermy blocking in the commercial bivalve species, Tegillarca granosa, using the specific inhibitors verapamil hydrochloride and N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide hydrochloride (W-7). The impacts of Ca-channel and CaM inhibition on polyspermy rates and oocyte membrane potential were studied microscopically using the fluorescent dyes Hochest 33258 and DiBAC4(3), respectively. The results showed that the inhibition of the Ca-channel and CaM led to a significant increase in polyspermy rates, which may be attributed to significant reductions in both amplitude and duration of membrane potential change during the depolarization process. These findings not only demonstrate that the Ca-channel and CaM play crucial roles in fast electrical polyspermy blocking, but also indicate that Ca might be essential for the depolarization process of oocytes of T. granosa.