Geomorphic gradients in shallow seagrass carbon stocks

Seagrass meadows are important sinks of organic carbon (C-org), in particular the near-surface C(org & nbsp;)pool (<= 15 cm) compared to deeper sediments. Near-surface carbon is highly susceptible to disturbance and loss to the atmosphere, however, inadequate accounting for variability in this pool of carbon limits their uptake into carbon accounting frameworks. We therefore investigated the spatial variability in seagrass near-surface C-org and biomass C-org across different geomorphic (estuary, lagoonal and reef-associated) and community typologies (pioneer and persistent). Near-surface C-org stock in vegetated areas (25.78 Mg C-org ha(-1) +/- 26.64) was twice that from unvegetated areas (14.27 Mg C-org ha(-1) +/- 15.86), reinforcing the paradigm that the presence of seagrass enhances carbon stocks. Lagoonal and reef-associated meadows showed similar C-org stocks (p > 0.05), which were substantially higher (p < 0.05) than estuary meadows. Likewise, persistent seagrass communities (Cymo-docea dominance) stored higher (p < 0.05) stocks of C-org than pioneer communities (Halophila and Halodule dominance). Linear regression models showed significant but weak relationships between seagrass cover, shoot density and standing biomass with near-surface C-org stocks, whereas significant and strong relationships were observed for organic matter, dry bulk density and median grain size. The results highlight the need for higher resolution carbon assessments to better understand local and regional variability, in order to better inform carbon accounting and conservation policy.

Automated summary

Seagrass meadows are important sinks of organic carbon, especially near-surface C(org) pool. This study investigated the spatial variability in seagrass near-surface C(org) and biomass C(org) across different geomorphic and community typologies. The results showed that near-surface C(org) stock in vegetated areas was higher than in unvegetated areas. Lagoonal and reef-associated meadows had higher C(org) stocks than estuary meadows, and persistent seagrass communities had higher C(org) stocks than pioneer communities.