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 role of restored seagrass meadows as carbon sources or sinks depends largely on organic carbon metabolism and carbonate dynamics. Here, we employed ex situ core incubation to quantify gross primary productivity (GPP), community respiration (R), net ecosystem metabolism (NEM), and net ecosystem calcification (NEC) in restored seagrass (SG) and adjacent bare sediment (BS). SG exhibited significantly higher GPP (26.0±3.4mmolO2m-2h-1 vs. 0.7±1.3mmolO2m-2h-1, p<0.01) and NEM (208.2±22.2mmolO2m-2d-1 vs. 20.1±9.9mmolO2m-2d-1, p<0.01) than BS, indicating enhanced autotrophy and carbon sink potential. SG also exhibited net calcification (10.9±15.7mmolCaCO3m-2d-1), while BS showed net dissolution (-2.3±18.8mmolCaCO3m-2d-1); however, high NEC variability resulted in no statistically significant difference (p>0.05). These findings suggest that restored seagrass enhances organic carbon sequestration despite variability in carbonate fluxes. Ex situ incubations enable simultaneous measurements of organic and inorganic carbon metabolism, although complementary in situ validation remains essential. Overall, this study highlights the potential of seagrass restoration to strengthen coastal carbon sinks and contribute to climate change mitigation.