Seaweed forests are carbon sinks that can mitigate CO2 emissions

The paper — Seaweed ecosystems may not mitigate CO2 emissions (Gallagher et al., 2022) — claims that seaweed ecosystems are carbon sources rather than carbon sinks because ‘respiration subsidies’ (from inputs of allochthonous organic carbon) create negative net ecosystem production. That is, that seaweed ecosystems produce more CO2 than they draw down, and thus may not mitigate CO2 emissions. They make this claim using a compiled dataset which shows that, on average, seaweed ecosystems are net heterotrophic. However, their assessment is flawed and conceptually misleading as key terms are misinterpreted, the data presented are biased, and the conclusions are not supported statistically. Here we discuss four flaws in the argument presented by Gallagher et al., which we believe risk confusing further research on seaweed blue carbon and unjustifiably seeding doubt around motivations and initiatives to protect and restore seaweed forests.