Abstract:

Coral reefs stand as remarkably productive ecosystems within the vast ocean, wherein their carbon cycle is meticulously regulated through a complex interplay of three pivotal metabolic processes: photosynthesis, respiration, and calcification. These intricate mechanisms contribute to the intricate and sophisticated functioning of these ecosystems, rendering them worthy subjects of extensive scholarly inquiry and analysis. To explore the carbon sequestration potential of corals and shed light on the underlying mechanisms in both illuminated and dark conditions, this research was conducted using Acropora hyacinthus and Galaxea fascicularis specimens collected from the Wuzhizhou Island, Sanya. Employing the carbonate system, an analysis was carried out to assess the carbon sequestration capabilities of these two coral species. This involved measuring the changes in physicochemical factors in the surrounding water before and after the experiment, as well as determining the content of dissolved inorganic carbon (DIC) and partial pressure of carbon dioxide (pCO₂) using CO₂ system calculation software. By employing these methodologies, a comprehensive understanding of the carbon sequestration processes within these coral species was achieved. The findings of this study demonstrated distinct responses of the water parameters for A. hyacinthus and G. fascicularis under light and dark conditions. In the presence of light, the water bodies surrounding both corals exhibited a decrease in total alkalinity (TA) and pondus hydrogenii (pH), an increase in water temperature (WT) and dissolved oxygen (DO), as well as continuous consumption of DIC and CO₂, resulting in a pronounced carbon sink effect. Conversely, under dark conditions, TA, pH, and WT increased, DO decreased, and DIC and CO₂ were consistently released, indicating a carbon source effect. By comparing the outcomes of light and dark treatments, the carbon sequestration rate of A. hyacinthus was calculated to be 0.00576 mol·m^-2·h^-1, while that of G. fascicularis was determined to be 0.00022 mol·m^-2·h^-1. Notably, the carbon sequestration efficiency of A. hyacinthus surpassed that of G. fascicularis significantly (P<0.05). Both corals exhibited a net absorption of CO₂ through photosynthesis, surpassing the amount they produced, thereby acting as CO₂ sinks. In summary, these two coral species effectively reduced the total alkalinity, DIC, and pCO₂ within the water column, facilitating the transfer of atmospheric CO₂ to seawater and engendering alkalinity sink and carbon sink effects.

Key words: Acropora hyacinthus, Galaxea fascicularis, dissolved inorganic, carbon sequestration capacity