ALBERT

Description: Although the effect of ocean acidification on fertilization success of marine organisms is increasingly well documented, the underlying mechanisms are not completely understood. The fertilization success of broadcast spawning invertebrates depends on successful sperm-egg collisions, gamete fusion, and standard generation of Ca2+oscillations. Therefore, the realistic effects of future ocean pCO2 levels on these specific aspects of fertilization of Tegillarca granosa were investigated in the present study through sperm velocity trials, fertilization kinetics model analysis, and intracellular Ca2+assays, respectively. Results obtained indicated that ocean acidification significantly reduced the fertilization success of T. granosa, which could be accountable by (i) decreased sperm velocity hence reducing the probability for sperm-egg collisions; (ii) lowered probability of gamete fusion for each gamete collision event; and (iii) disrupted intracellular Ca2+ oscillations.

Description: 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, IKKalpha and Myd88), and effectors (NF-kB) 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.

Description: 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.

Description: The impact of pCO2 driven ocean acidification on marine bivalve immunity remains poorly understood. To date, this impact has only been investigated in a few bivalve species and the underlying molecular mechanism remains unknown. In the present study, the effects of the realistic future ocean pCO2 levels (pH at 8.1, 7.8, and 7.4) on the total number of haemocyte cells (THC), phagocytosis status, blood cell types composition, and expression levels of twelve genes from the NF-kappa beta signaling and toll-like receptor pathways of a typical bottom burrowing bivalve, blood clam (Tegillarca granosa), were investigated. The results obtained showed that while both THC number and phagocytosis frequency were significantly reduced, the percentage of red and basophil granulocytes were significantly decreased and increased, respectively, upon exposure to elevated pCO2. In addition, exposure to pCO2 acidified seawater generally led to a significant down-regulation in the inducer and key response genes of NF-kappa beta signaling and toll-like receptor pathways. The results of the present study revealed that ocean acidification may hamper immune responses of the bivalve T. granosa which subsequently render individuals more susceptible to pathogens attacks such as those from virus and bacteria.

Description: Although the effect of ocean acidification on fertilization success of marine organisms is increasingly well documented, the underlying mechanisms are not completely understood. The fertilization success of broadcast spawning invertebrates depends on successful sperm-egg collisions, gamete fusion, and standard generation of Ca2+oscillations. Therefore, the realistic effects of future ocean pCO2 levels on these specific aspects of fertilization of Tegillarca granosa were investigated in the present study through sperm velocity trials, fertilization kinetics model analysis, and intracellular Ca2+assays, respectively. Results obtained indicated that ocean acidification significantly reduced the fertilization success of T. granosa, which could be accountable by (i) decreased sperm velocity hence reducing the probability for sperm-egg collisions; (ii) lowered probability of gamete fusion for each gamete collision event; and (iii) disrupted intracellular Ca2+ oscillations.

Description: 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.

Description: Since the industrial revolution, massive amount of anthropogenic carbon dioxide (CO2) have been generated to elevate the atmospheric CO2 concentration. Some anthropogenic CO2 have been absorbed by the ocean to cause “ocean acidification” (OA). Although the negative impacts of OA on sperm motility are increasingly found in various marine invertebrate species, the cellular and molecular mechanisms for these effects are still poorly understood. This study investigated the effect of OA (pH7.8 and 7.4) on sperm motility and energy supplying pathway in blood clam Tegillarca granosa. The results showed that the sperm swimming speed reduced significantly in acidified seawater. Since the adenosine triphosphate (ATP) level of sperm is closely related to its motility, we analyzed the sperm ATP content and activities of key enzymes during ATP synthesis under different OA scenarios. OA treatments significantly reduced ATP content as well as activities of 6-phosphofructokinase and pyruvate kinase in the sperm of T. granosa. The sperm Ca2+-ATPase of various animals has been reported to regulate sperm motility. Therefore, we explored the Ca2+-ATPase activity of T. granosa sperm under OA treatment. The results found that Ca2+-ATPase activities in the sperm of T. granosa were significantly declined under OA scenarios. In conclusion, these results suggested that OA could constrain sperm motility through inhibiting ATP synthesis and disturbing intracellular Ca2+ regulation.

Description: In recent years, ocean acidification (OA) caused by oceanic absorption of anthropogenic carbon dioxide (CO2) has drawn worldwide concern over its physiological and ecological effects on marine organisms. However, the behavioral impacts of OA and especially the underlying physiological mechanisms causing these impacts are still poorly understood in marine species. Therefore, in the present study, the effects of elevated pCO2 on foraging behavior, in vivo contents of two important neurotransmitters, and the expression of genes encoding key modulatory enzymes from the olfactory transduction pathway were investigated in the larval black sea bream. The results showed that larval sea breams (length of 4.71 +- 0.45 cm) reared in pCO2 acidified seawater (pH at 7.8 and 7.4) for 15 days tend to stall longer at their acclimated zone and swim with a significant slower velocity in a more zigzag manner toward food source, thereby taking twice the amount of time than control (pH at 8.1) to reach the food source. These findings indicate that the foraging behavior of the sea bream was significantly impaired by ocean acidification. In addition, compared to a control, significant reductions in the in vivo contents of gama-aminobutyric acid (GABA) and Acetylcholine (ACh) were detected in ocean acidification-treated sea breams. Furthermore, in the acidified experiment groups, the expression of genes encoding positive regulators, the olfaction-specific G protein (Golf) and the G-protein signaling 2 (RGS2) and negative regulators, the G protein-coupled receptor kinase (GRK) and arrestin in the olfactory transduction pathway were found to be significantly suppressed and up-regulated, respectively. Changes in neurotransmitter content and expression of olfactory transduction related genes indicate a significant disruptive effect caused by OA on olfactory neural signal transduction, which might reveal the underlying cause of the hampered foraging behavior.

Description: The current knowledge about the effect of pCO2-driven ocean acidification on the bioaccumulation of pollutants in marine species is still scarce, as only limited types of pollutants have been investigated. Therefore, to obtain a better understanding of the effect of ocean acidification on the process of bioaccumulation and subsequent food safety, the accumulation of benzo[a]pyrene (B[a]P), chloramphenicol (CAP), and nitrofurazone (NFZ) in an edible bivalve species, Tegillarca granosa, under present and near-future ocean acidification scenarios was investigated in the present study. The health risks associated with consuming contaminated blood clams were also assessed using target hazard quotient (THQ), lifetime cancer risk (CR), or margin of exposure (MoE). To explain the alterations in bioaccumulation of these pollutants, the expressions of genes encoding corresponding key metabolic proteins were analyzed as well. The results obtained showed that ocean acidification exerted a significant effect on the accumulation of B[a]P, NFZ, and CAP in the clams. After four-week exposure to B[a]P, NFZ, or CAP contaminated seawater acidified with CO2 at pH 7.8 and 7.4, significantly greater amounts of B[a]P and lower amounts of NFZ and CAP were accumulated in the clams compared to that in the control. Although no non-carcinogenic risk of consuming B[a]P-contaminated blood clams was detected using the THQ values obtained, the CR values obtained indicated a high life-time risk in all groups. In addition, according to the MoE values obtained, the health risks in terms of consuming NFZ- and CAP-contaminated clams were significantly reduced under ocean acidification scenarios but still cannot be ignored, especially for children. The gene expression results showed that the ability of clams to eliminate B[a]P may be significantly constrained, whereas the ability to eliminate NFZ and CAP may be enhanced under ocean acidification scenarios, indicating that the changes in the accumulation of these pollutants may be due to the altered in vivo metabolism.