Multiple Factors Driving Carbonate System in Subtropical Coral Community Environments along Dapeng Peninsula, South China Sea

Abstract

Coral reef ecosystems have extremely high primary productivity and play an important role in the marine carbon cycle. However, due to the high carbon metabolism efficiency of coral communities, little is known about the carbon sink–source properties of coral reefs. In November 2022, in situ field investigations coupled with incubation experiments were conducted in typical subtropical coral reef waters, i.e., Yangmeikeng Sea Area (Area I) and Dalu Bay (Area Ⅱ), to explore the dynamics of the carbonate system and its controlling factors. The results revealed that the carbonate parameters had high variability, comprehensively forced by various physical and biochemical processes. Overall, Areas I and Ⅱ were net sinks of atmospheric CO2, with net uptake fluxes of 1.66 ± 0.40 and 0.99 ± 0.08 mmol C m−2 day−1, respectively. The aragonite saturation state (ΩA), 3.04–3.87, was within the range adequate for growth of tropical shallow-water scleractinian corals. Inorganic carbon budget results indicated that photosynthesis and microbial respiration were the main factors affecting the dynamics of carbonate systems in the whole study area. However, focusing on the reef areas, coral metabolism was also a key factor affecting the carbonate system in seawater (especially in Area I) and its contribution accounted for 28.9–153.3% of the microbial respiration. This study highlighted that metabolism of coral communities could significantly affect the seawater carbonate system, which is of great significance in the context of the current process of ocean acidification.

Seasonal Controls of Seawater CO2 Systems in Subtropical Coral Reefs: A Case Study from the Eastern Coast of Shenzhen, China

“…column of the DAB, DLB, and YMKSA by 0.16 ± 0.03 µmol kg −1 , 0.03 ± 0.01 µmol kg −1 , and 0.21 ± 0.04 µmol kg −1 per month; correspondingly, this process increased the DIC by 3.57 ± 0.54 µmol kg −1 , 0.81 ± 0.12 µmol kg −1 , and 4.65 ± 0.70 µmol kg −1 , respectively. A previous study indicated that, in autumn, the microbial respiration of seawater in here can simultaneously reduce the concentration of TA by 14.4-22.8 µmol kg −1 and increase the concentration of DIC by 90.0-168 µmol kg −1 per month [28]. In comparison, the effect of coral metabolism on TA and DIC was much lower than that of microbial respiration.…”

“…In addition, the focus on coastal coral reef habitats, the metabolic activities of corals, and reef organisms may also have an important effect on the seawater CO 2 system because of the formation of biological calcium carbonate and respiration [27,28]. Generally, coral calcification absorbs total alkalinity (TA) and DIC at a ratio of 2:1 from seawater, resulting in an increase in the pCO 2 and a decrease in the pH and Ω A of the seawater, and vice versa [29].…”