Negligible Greenhouse Gas Release from Sediments in Oyster Habitats

After centuries of decline, oyster populations are now on the rise in coastal systems globally following aquaculture development and restoration efforts. Oysters regulate the biogeochemistry of coastal systems in part by promoting sediment nutrient recycling and removing excess nitrogen via denitrification. Less clear is how oysters alter sediment greenhouse gas (GHG) fluxes-an important consideration as oyster populations grow. Here, we show that sediments in oyster habitats produce carbon dioxide (CO₂), with highest rates in spring (2396.91 ± 381.98 μmol CO₂ m^-2 h^-1) following deposition of seasonal diatom blooms and in summer (2795.20 ± 307.55 μmol CO₂ m^-2 h^-1) when temperatures are high. Sediments in oyster habitats also consistently released methane to the water column (725.94 ± 150.34 nmol CH₄ m^-2 h^-1) with no seasonal pattern. Generally, oyster habitat sediments were a sink for nitrous oxide (N₂O; -36.11 ± 7.24 nmol N₂O m^-2 h^-1), only occasionally releasing N₂O in spring. N₂O release corresponded to high organic matter and dissolved nitrogen availability, suggesting denitrification as the production pathway. Despite potential CO₂ production increases under aquaculture in some locations, we conclude that in temperate regions oysters have an overall negligible impact on sediment GHG cycling.