Abstract
The rising anthropogenic atmospheric CO2 results in the reduction of seawater pH, namely ocean acidification (OA). In East China Sea, the largest coastal hypoxic zone was observed in the world. This region is also strongly impacted by ocean acidification as receiving much nutrient from Changjiang and Qiantangjiang, and organisms can experience great short-term natural variability of DO and pH in this area. In order to evaluate the defense responses of marine mussels under this scenario, the thick shell mussel Mytilus coruscus were exposed to three pH/pCO2 levels (7.3/2800 μatm, 7.7/1020 μatm, 8.1/376 μatm) at two dissolved oxygen concentrations (DO, 2.0, 6.0 mg L−1) for 72 h. Results showed that byssus thread parameters, such as the number, diameter, attachment strength and plaque area were reduced by low DO, and shell-closing strength was significantly weaker under both hypoxia and low pH conditions. Expression patterns of genes related to mussel byssus protein (MBP) were affected by hypoxia. Generally, hypoxia reduced MBP1 and MBP7 expressions, but increased MBP13 expression. In conclusion, both hypoxia and low pH induced negative effects on mussel defense responses, with hypoxia being the main driver of change. In addition, significant interactive effects between pH and DO were observed on shell-closing strength. Therefore, the adverse effects induced by hypoxia on the defense of mussels may be aggravated by low pH in the natural environments.
Highlights
Anthropogenic CO2 emissions are driving increases in the net CO2 uptake by the oceans
The relative expression level of the gene associated with mussel byssus protein1 (MPB1) was significantly affected by DO, time and their interactions
The shell-closing strength was weakened upon exposure to these conditions, showing that short term exposure to low pH and DO can impair the mussel’s defense capacity
Summary
Anthropogenic CO2 emissions are driving increases in the net CO2 uptake by the oceans. Decreased pH results in profound modification of the seawater carbonate chemistry including a reduction of the calcite saturation state [ cal = ([Ca2+][CO23−]/Ksp), where sp is the solubility product at a assumed pressure, temperature and salinity]. DO levels in warmer waters are lower, and global warming enhances the stratification of the upper ocean These two factors decrease the supply of oxygen to the deeper parts of the ocean, spreading out hypoxic zones (Pörtner et al, 2005; Keeling et al, 2009; Feely et al, 2010; Stramma et al, 2010). Eutrophication usually exacerbates hypoxia in offshore waters (Levin et al, 2009)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
