CO2-induced ocean acidification increases anxiety in Rockfish via alteration of GABAA receptor functioning

The average surface pH of the ocean is dropping at a rapid rate due to the dissolution of anthropogenic CO2, raising concerns for marine life. Additionally, some coastal areas periodically experience upwelling of CO2-enriched water with reduced pH. Previous research has demonstrated ocean acidification (OA)-induced changes in behavioural and sensory systems including olfaction, which is due to altered function of neural gamma-aminobutyric acid type A (GABAA) receptors. Here, we used a camera-based tracking software system to examine whether OA-dependent changes in GABAA receptors affect anxiety in juvenile Californian rockfish (Sebastes diploproa). Anxiety was estimated using behavioural tests that measure light/dark preference (scototaxis) and proximity to an object. After one week in OA conditions projected for the next century in the California shore (1125 ± 100 µatm, pH 7.75), anxiety was significantly increased relative to controls (483 ± 40 µatm CO2, pH 8.1). The GABAA-receptor agonist muscimol, but not the antagonist gabazine, caused a significant increase in anxiety consistent with altered Cl- flux in OA-exposed fish. OA-exposed fish remained more anxious even after 7 days back in control seawater; however, they resumed their normal behaviour by day 12. These results show that OA could severely alter rockfish behaviour; however, this effect is reversible.

Ocean acidification weakens the immune response of blood clam through hampering the NF-kappa beta and toll-like receptor pathways

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.