Effects of seawater acidification and thermal stress on the antioxidant responses and energy metabolism of Alpheus japonicus and Hemicentrotus pulcherrimus
Due to the over burning of large amounts of fossil fuels, deforestation and other anthropogenic activities, the amount of CO2 in the atmosphere is gradually increasing. When a large amount of CO2 enters the ocean, it can cause a decrease of the seawater pH and a change of carbonate chemistry. This phenomenon is termed ocean acidification (seawater acidification). Meanwhile, the large amount of CO2 and other greenhouse gas emissions will also lead to a rise of seawater temperature, namely the ocean warming. With the increasing global climate change, the phenomenon of ocean acidification and warming caused by excessive CO2 emissions has attracted widespread attention. Coastal waters are greatly affected by human activities, where the survival and health of coastal organisms are increasingly threatened by multiple environmental pressures such as ocean acidification and warming. Till now, most studies focus on the impact of single environmental pressure on marine organisms, and the research on the coupling effect under multiple pressures is still very limited. Alpheus japonicus (crustaceans) and Hemicentrotus pulcherrimus (echinoderms) are two common marine species with both ecological and commercial value, which also play a key role in the health and stability of offshore ecosystems. In this study, we combined seawater acidification and warming exposure to these two groups, with a purpose to clarify the physiological damage of multiple pressures to key offshore marine organisms. The related results can provide a scientific basis for the response strategies and control mechanisms of key offshore biological groups under the pressure of climate change. This study includes the following two parts:1. Effects of seawater acidification and thermal stress on physiological processes such as oxidative stress and energy metabolism of A. japonicus. Our results suggested that both seawater acidification and elevated thermal stress induced oxidative response of A. japonicus; concurrent seawater acidification and thermal stress had interactive effects on the CAT activities and GSH/GSSG ratio of A. japonicus. The HK activities increased and the PROT content reduced after a 14-day exposure, which demonstrated disturbances in glycolysis and energy reserves, and indicated that the energy metabolism strategy adopted by A. japonicus was unsustainable in long term. 2. Effects of seawater acidification and thermal stress on physiological responses of H. pulcherrimus, taking oxidative stress and energy metabolism as examples. The results showed that seawater acidification and thermal stress treatment had a synergistic effect on GSH content, GSH/GSSG ratio and LPO level of H. pulcherrimus. The response trends of glycolytic enzymes PK and HK to seawater acidification and thermal stress of H. pulcherrimus were similar. At the same time, seawater acidification and thermal stress affected the digestion process and energy reserve of the sea urchin. The activities of AKP and Tryp was significantly enhanced and the content of glycogen was significantly reduced in thermal stress treatment, indicating that the sea urchin may increase digestive enzyme activities and glycogen consumption to maintain the steady state of their energy systems. Both seawater acidification and thermal stress have led to oxidative stress to the studied shrimp and sea urchin. The antioxidant defense system and energy distribution strategy of these two organisms ensure their physiological stability and health. These results suggested that short-term seawater acidification and elevated thermal stress could trigger oxidative stress and disturbance in energy metabolism of A. japonicus and H. pulcherrimus, which would affect population replenishment of these species under increased ocean acidity and thermal stress in the long run. Moreover, due to the different affiliations and living habits, shrimp and sea urchin have adopted variable physiological responses and energy strategies in coping with environmental stress.
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