Seagrass decline weakens sediment organic carbon stability

Area of Science:

• Marine Ecology
• Carbon Sequestration
• Coastal Ecosystems

Background:

• Seagrass meadows are vital blue carbon sinks, crucial for mitigating climate change.
• Seagrass decline due to human activities and climate change threatens their carbon storage capacity.
• The impact of seagrass loss on the stability of stored sediment organic carbon (SOC) remains poorly understood.

Purpose of the Study:

• To investigate how seagrass degradation affects sediment organic carbon (SOC) and recalcitrant SOC (RSOC) stocks and stability.
• To quantify the relationship between seagrass health indicators (density, biomass, coverage) and carbon storage.
• To provide insights for effective coastal carbon protection strategies.

Main Methods:

• Analysis of total SOC and RSOC at 15 cm depth in nine Southern China seagrass meadows.
• Comparison of carbon stocks across different seagrass species (Halophila spp., Thalassia hemprichii, Enhalus acoroides).
• Statistical analyses (redundancy and correlation) to link seagrass metrics with carbon parameters.

Main Results:

• The recalcitrant SOC to SOC ratio (RSOC/SOC) ranged from 27% to 91% and increased slightly with depth.
• SOC and RSOC stocks were significantly higher in Halophila spp. meadows compared to T. hemprichii and E. acoroides meadows.
• Declining seagrass shoot density, biomass, and coverage correlated with reduced SOC and RSOC content, stock, and RSOC/SOC ratio, indicating decreased carbon sequestration stability.

Conclusions:

• Seagrass loss diminishes the stability and quantity of blue carbon stored in sediments.
• Unvegetated areas showed substantial decreases in RSOC compared to adjacent seagrass meadows.
• Preserving and restoring seagrass meadows are essential for maximizing blue carbon sequestration and developing robust coastal carbon strategies.