Estimation of Metabolic Dynamics of Restored Seagrass Meadows in a Southeast Asia Islet: Insights from Ex Situ Benthic Incubation

Abstract. Seagrass meadows are vital carbon sinks, but their function is threatened by rapid decline, driving restoration efforts to enhance coastal recovery and carbon removal. The capacity of these restored seagrass as carbon sources or sinks depends largely on organic carbon metabolism and carbonate dynamics. In this study, we employed ex situ core incubation to investigate the metabolic rates of replanted seagrasses (SG), including gross primary productivity (GPP), community respiration (R), net ecosystem metabolism (NEM), and net ecosystem calcification (NEC) in SG and surrounding bare sediments (BS). SG exhibited higher GPP (26.0 ± 1.0 mmol O₂ m^-2 h^-1 vs 0.7 ± 0.1 mmol O₂ m^-2 h^-1) and NEM (208.2 ± 6.3 mmol O₂ m^-2 d^-1 vs 20.1 ± 2.8 mmol O₂ m^-2 d^-1) than BS, indicating their potential as carbon sinks by shifting benthic metabolism towards a more autotrophic state. In contrast, SG showed higher daytime carbonate production and nighttime carbonate dissolution, which could offset each other, resulting in no significant difference in NEC between SG and BS. In summary, our results found that the SG exhibited significantly higher NEM compared to BS, while no significant difference was found for NEC. Consequently, the net effect on the carbon uptake capacity of the restored seagrass is likely increased, primarily due to the higher NEM. Our findings highlight the ecological significance of seagrass restoration in mitigating climate change through carbon removal. Ex situ core incubation method allows for the simultaneous measurement of organic and inorganic carbon metabolism. While ex situ core incubation enhances feasibility, in situ assessments are still necessary to validate the results and ensure a comprehensive understanding of seagrass ecosystem dynamics.