Effect of seagrass cover loss on seawater carbonate chemistry: Implications for the potential of seagrass meadows to mitigate ocean acidification

Abstract

Seagrass meadows are important marine ecosystems for mitigating ocean acidification because of their ability to raise the pH of seawater during the day. This ability may decrease as a result of the loss of these meadows, which is primarily caused by human activities and climate change. Here, we test the effect of seagrass cover loss on seawater carbonate chemistry to understand how the loss of seagrass meadows affects their ability to mitigate ocean acidification. pH, dissolved inorganic carbon (DIC), partial pressure of carbon dioxide (pCO2), and aragonite saturation state (ΩAr) were measured in experimental tidal pools with varying proportions of seagrass coverage: 0% (mimicking a complete loss of seagrass meadows); 1%–29% (mimicking the greatest loss of seagrass meadows); 30%–59% (mimicking a moderate loss of seagrass meadows); and 60%–100% (mimicking the lowest loss of seagrass meadows). It was found that as seagrass cover decreased, pH and ΩAr levels in seawater decreased proportionally during the day, while pCO2 and DIC increased. Additionally, correlation analysis showed a strong significant positive correlation between the seagrass cover and pH (rs = 0.9096, p < 0.0001) and ΩAr (rs = 0.9031, p < 0.0001), as well as a strong significant negative correlation between the seagrass cover and pCO2 (rs = −0.9068, p < 0.0001) and DIC (rs = −0.8947, p < 0.0001). These results imply that the 7% annual global loss in seagrass meadows may limit seagrass meadows’ ability to raise the pH of their surrounding seawater during the day, reducing their potential to mitigate ocean acidification. The study recommends that management strategies that minimize anthropogenic activities that cause seagrass loss be implemented in order for seagrass meadows to continue mitigating ocean acidification within their ecosystem and nearby ecosystems.