Growing evidence suggests that ocean acidification (OA) may affect animal behaviors such as feeding. Although gustation plays a crucial role in evaluating the quality and palatability of food and ultimately influences whether or not teleosts consume the food, the potential impact of OA on gustation-mediated feeding behavior remains unknown. In this study, gustation mediated-feeding behavior, as indicated by the consumption rate (CR) and swallowing rate (SR) of agar pellets with or without feed upon OA exposure was investigated in black sea bream (Acanthopagrus schlegelii). Results showed that the exposure to acidified seawater led to significant reductions in the CR and SR of feed-containing agar pellets. In addition, the in vivo contents of three neurotransmitters and expression of genes from the gustatory signal transduction pathway were all significantly suppressed by the OA treatment. In general, the data obtained indicated that OA may hinder the gustation-mediated feeding behavior of A. schlegelii by disrupting gustatory signal transduction, which may aggravate the issue of food shortage for wild populations of black sea bream.

Large amounts of anthropogenic CO2 in the atmosphere are taken up by the ocean, which leads to 'ocean acidification' (OA). In addition, the increasing application of nanoparticles inevitably leads to their increased release into the aquatic environment. However, the impact of OA on the bioaccumulation of nanoparticles in marine organisms still remains unknown. This study investigated the effects of OA on the bioaccumulation of a model nanoparticle, titanium dioxide nanoparticles (nTiO2), in three edible bivalves. All species tested accumulated significantly greater amount of nTiO2 in pCO2-acidified seawater. Furthermore, the potential health threats of realistic nTiO2 quantities accumulated in bivalves under future OA scenarios were evaluated with a mouse assay, which revealed evident organ edema and alterations in hematologic indices and blood chemistry values under future OA scenario (pH at 7.4). Overall, this study suggests that OA would enhance the accumulation of nTiO2 in edible bivalves and may therefore increase the health risk for seafood consumers.

An enormous amount of anthropogenic carbon dioxide (CO2) has been dissolved into the ocean, leading to a lower pH and changes in the chemical properties of seawater, which has been termed ocean acidification (OA). The impacts of pCO2-driven acidification on immunity have been revealed recently in various marine organisms. However, the mechanism causing the reduction in phagocytosis still remains unclear. Therefore, the impacts of pCO2-driven OA at present and near-future levels (pH values of 8.1, 7.8, and 7.4) on the rate of phagocytosis, the abundance of cytoskeleton components, the levels of nitric oxide (NO), and the concentration and activity of lysozymes (LZM) of hemocytes were investigated in a commercial bivalve species, the blood clam (Tegillarca granosa). In addition, the effects of OA on the expression of genes regulating actin skeleton and nitric oxide synthesis 2 (NOS2) were also analyzed. The results obtained showed that the phagocytic rate, cytoskeleton component abundance, concentration and activity of LZM of hemocytes were all significantly reduced after a 2-week exposure to the future OA scenario of a pH of 7.4. On the contrary, a remarkable increase in the concentration of NO compared to that of the control was detected in clams exposed to OA. Furthermore, the expression of genes regulating the actin cytoskeleton and NOS were significantly up-regulated after OA exposure. Though the mechanism causing phagocytosis seemed to be complicated based on the results obtained in the present study and those reported previously, our results suggested that OA may reduce the phagocytosis of hemocytes by (1) decreasing the abundance of cytoskeleton components and therefore hampering the cytoskeleton-mediated process of engulfment, (2) reducing the concentration and activity of LZM and therefore constraining the degradation of the engulfed pathogen through an oxygen-independent pathway, and (3) inducing the production of NO, which may negatively regulate immune responses.

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.

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.

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.

It has been suggested that climate change may promote the outbreaks of diseases in the sea through altering the host susceptibility, the pathogen virulence, and the host-pathogen interaction. However, the impacts of ocean acidification (OA) on the pathogen components of bacterial community and the host-pathogen interaction of marine bivalves are still poorly understood. Therefore, 16S rRNA high-throughput sequencing and host-pathogen interaction analysis between blood clam (Tegillarca granosa) and Vibrio harveyi were conducted in the present study to gain a better understanding of the ecological impacts of ocean acidification. The results obtained revealed a significant impact of ocean acidification on the composition of microbial community at laboratory scale. Notably, the abundance of Vibrio, a major group of pathogens to many marine organisms, was significantly increased under ocean acidification condition. In addition, the survival rate and haemolytic activity of V. harveyi were significantly higher in the presence of haemolymph of OA treated T. granosa, indicating a compromised immunity of the clam and enhanced virulence of V. harveyi under future ocean acidification scenarios. Conclusively, the results obtained in this study suggest that future ocean acidification may increase the risk of Vibrio pathogen infection for marine bivalve species, such as blood clams.

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.