|Other Abstract||In recent years, industrial and agricultural activities such as the burning of fossil energy and deforestation have emitted a large amount of CO2 into the atmosphere. After the ocean absorbs approximately 1/3 of CO2, the pH value of the seawater continues to decrease, and the temperature of the seawater continues to increase due to the aggravation of the greenhouse effect. In addition, human activities also emit a large amount of pollutants into the ocean, including antibiotics, persistent organic pollutants, heavy metals, petroleum and plastic products, causing serious damage to the marine environment. Consequently, survival and reproduction of marine organisms and structure and function of ecosystem are under grave threat.
Coral reef ecosystems have the most complex community structure on the planet and underpin a range of ecosystem goods and services for human societies. At present, coral reefs in the South China Sea are threaten by climate change and human activities, it is estimated that the coverage of coral in the area is less than 10%. Trochus niloticus is an important herbivorous gastropod in the coral reef ecosystem of the South China Sea. It can effectively control the algae biomass as grazers and ensure the domination of coral in coral reef ecosystem. This study aims to assess the physiological status of the key species T. niloticus in the coral reef ecosystem of the South China Sea, and to provide basic data for its population dynamics assessment and coral reef ecosystem environmental risk assessment under future climate and environmental conditions. The research mainly includes the following parts:
(1) Physiological responses of Trochus niloticus to seawater acidification combined with thermal stress exposure: The large amount of CO2 released into the atmosphere by human activities has caused serious impacts on the marine environment, mainly including ocean acidification and warming, which often occur simultaneously and have synergistic or antagonistic effects on marine organisms. In order to figure out the physiological responses of the key species in the coral reef ecosystem of the South China Sea, T. niloticus was exposed to ocean acidification and/or thermal stress for 28 days. The results show that both seawater acidification and thermal stress alone can induce immune responses and oxidative stress of T. niloticus, which could consume more energy reserves and result in the adjustment of energy allocation in T. niloticus. According to the results of integrated biomarker response, co-exposure of ocean acidification and thermal stress in this experiment caused the most severe pressure on T. niloticus, leading to reduced immunity, impaired oxidative balance, neurotoxicity and disorder of energy metabolism.
(2) Physiological responses of Trochus niloticus to seawater acidification combined with sulfamethoxazole exposure: In addition to the disturbances caused by climate change, marine organisms were also facing numerous stressors such as environmental pollution. The results are complicated and hard to predict when marine organisms facing multiple environmental stress. Sulfamethoxazole is a typical antibiotic found in the South China Sea, and its degradation process in the environment is affected by environmental factors such as seawater pH. In this study, the immune defense, oxidative stress and energy metabolism of T. niloticus were investigated after 28 days of exposure to ocean acidification and/or sulfamethoxazole. It was found seawater acidification exposure induced immune and anti-oxidant responses, as well as change of energy distribution in T. niloticus. Sulfamethoxazole exposure could stimulate antioxidant reactions and oxygen consumption in T. niloticus, indicating that topshells could acclimate to the stress of sulfamethoxazole through adjustment of its physiological state. However, under the co-exposure condition, a series of negative impacts were observed in T. niloticus, including impaired immune system which manifest as reduction of phagocytosis; excessive reactive oxygen species leading to oxidative stress; reduction of lipid and glycogen content and increased activity of electron transport system in digestive glands indicative of impaired cellular energy allocation. It was suggested that T. niloticus cannot cope with the stress caused by co-exposure, and these physiological alterations have potential effects on the survival and reproduction of T. niloticus in the long run.|