Global coral reef ecosystems have been severely degraded due to the combined effects of climate change and human activities. Changes in the seawater carbonate system of coral reef ecosystems can reflect their status and their responses to the impacts of climate change and human activities. Winter and summer surveys in 2019 found that the ecological community of the Luhuitou coral reef flat was dominated by macroalgae and corals, respectively, contrasting with the conditions 10 years ago. The Luhuitou fringing reefs were sources of atmospheric CO2 in both seasons. In winter, the daily variation range of dissolved inorganic carbon (DIC) in Luhuitou coral reefs was up to 450 µmol/kg, while that of total alkalinity (TA) was only 68 µmol/kg. This indicated that the organic production was significantly higher than the calcification process during this period. The TA/DIC was approximately 0.15, which was less than half of that in healthy coral reefs; hence, photosynthesis-respiration processes were the most important factors controlling daily changes in the seawater carbonate system. The net community production (NCP) of the Luhuitou coral reef ecosystem in winter was as high as 47.65 mmol C/(m2·h). While the net community calcification (NCC) was approximately 3.35 and −4.15 mmol CaCO3/(m2·h) during the daytime and nighttime respectively. Therefore, the NCC for the entire day was −21.9 mmol CaCO3/(m2·d), indicating a net autotrophic dissolved state. In summer, the acidification was enhanced by thunderstorms and heavy rain with the highest seawater partial pressure of CO2 (pCO2) and lowest pHT. Over the past 10 years, the increase rate of seawater pCO2 in Luhuitou reef was approximately 13.3 µatm/a***, six times that of the open ocean, while the decrease rate of pH was approximately 0.008 3/a, being five times that of the global ocean. These findings underscore the importance of protecting and restoring Luhuitou fringing reef, as well as similar reefs worldwide.
Zhang, J., Huang, H., Yuan, X., Luo Y., Liang H., Liang P. & Xu X. in press. The dilemma of Luhuitou fringing reefs: net dissolution in winter and enhanced acidification in summer. Journal of Oceanology and Limnology. Article.
