Risks to the stability of coral reefs in the South China Sea: An integrated biomarker approach to assess the physiological responses of Trochus niloticus to ocean acidification and warming

Abstract Scientific researches have clearly indicated that ocean acidification and warming poses serious threats to coral reef ecosystems. In coral reef ecosystems, herbivorous gastropods have an important function in maintaining the stability of the ecosystem due to controlling the abundance and growth of macroalgal, which compete for nutrients and space with coral. However, limited knowledge is available on the physiological responses of the specific keystone species to the increased ocean acidity and thermal stress. In this study, we evaluated the effects of ocean acidification (OA) and warming (OW) on an herbivorous gastropod Trochus niloticus commonly found on intertidal and shallow subtidal coral reefs in the South China Sea, on the aspect of immune responses (total hemocyte counts, reactive oxygen species level and apoptosis rate), oxidative stress (lipid peroxidation level, antioxidant enzyme activities), neurotoxicity (acetylcholinesterase activity), and energy metabolism (respiration rate and cellular energy allocation), after a 28-day exposure experiment to acidic (pH 7.6) and/or thermal (30 °C) seawater. Our results demonstrated that both OA and OW could lead to physiological disturbances of the herbivorous top-shells, including impaired immune functions and oxidative balance, neurotoxicity, and disorder of energy metabolism. Furthermore, results of integrated biomarker response (IBR) confirmed that the overall fitness of T. niloticus were deleteriously impacted by OA and OW, and were more stressed under the co-exposure condition. These results indicated that increased acidity and temperature in the future ocean might impair the viability of T. niloticus in the long-run, which will indulge the proliferation of macroalgae and lead to degradation of the coral reef ecosystem.