Seagrass blue carbon dynamics in the Gulf of Mexico: Stocks, losses from anthropogenic disturbance, and gains through seagrass restoration

Abstract

Seagrasses comprise a substantive North American and Caribbean Sea blue carbon sink. Yet fine-scale estimates of seagrass carbon stocks, fluxes from anthropogenic disturbances, and potential gains in sedimentary carbon from seagrass restoration are lacking for most of the Western Hemisphere. To begin to fill this knowledge gap in the subtropics and tropics, we quantified organic carbon (C_org) stocks, losses, and gains from restorations at 8 previously-disturbed seagrass sites around the Gulf of Mexico (GoM) (n=128 cores). Mean natural seagrass C_org stocks were 25.7±6.7MgC_orgha^-1 around the GoM, while mean C_org stocks at adjacent barren sites that had previously hosted seagrass were 17.8MgC_orgha^-1. Restored seagrass beds contained a mean of 38.7±13.1MgC_orgha^-1. Mean C_org losses differed by anthropogenic impact type, but averaged 20.98±7.14MgC_orgha^-1. C_org gains from seagrass restoration averaged 20.96±8.59Mgha^-1. These results, when combined with the similarity between natural and restored C_org content, highlight the potential of seagrass restoration for mitigating seagrass C_org losses from prior impact events. Our GoM basin-wide estimates of natural C_org totaled ~36.4Tg for the 947,327ha for the USA-GoM. Including Mexico, the total basin contained an estimated 37.2-37.5Tg C_org. Regional US-GoM losses totaled 21.69Tg C_org. C_org losses differed significantly among anthropogenic impacts. Yet, seagrass restoration appears to be an important climate change mitigation strategy that could be implemented elsewhere throughout the tropics and subtropics.

Keywords: Blue carbon; Gulf of Mexico; Seagrass carbon; Seagrass impact carbon loss; Seagrass restoration.