Kelps are large brown macroalgae which can grow extremely fast, with reported growth rates of up to half a metre a day. They develop dense forests, ultimately reaching 30 to 80 meters high, throughout temperate and polar oceans worldwide and provide numerous benefits critical to human well-being and the biodiversity that they support. Kelps are among the most productive ecosystems in the world, rivaling agricultural fields and tropical rainforests.
Kelps are either hard-bottom or free-floating species. Their fronds can reduce flow velocity and facilitate the settlement of particles, although these cannot be buried beneath the canopy due to the lack of true roots. As a result, they have not been considered as important as the other “blue carbon” habitats in storing carbon, and so are not included in current climate mitigation efforts and mechanisms.
However, should macroalgae be included as a blue carbon ecosystem?
In a word - yes. The latest research has revealed some important facts about kelp. It was previously thought that kelps were either rapidly consumed by marine animals or degraded and released back into the atmosphere in the form of CO2. New evidence, however, shows that they can travel along the seafloor or float at the surface until ocean currents pull them down. Eventually they get buried inside deep sea canyons, so the carbon is effectively trapped. Macroalgae have been estimated to sequester about 173 Tg C yr–1 on a global scale, an estimate that exceeds that for carbon sequestered in vegetated coastal habitats. Also, macroalgae cover an area of about 3.5 million square kilometres, three times greater than seagrasses, mangroves and saltmarshes combined. Are macroalgae important in global carbon sequestration? We will let you do the math.
Another prerequisite for macroalgae to be included in blue carbon assessments is to demonstrate that their carbon has been sequestered over centennial or millennial timescales. Macroalgae are reported to be the source of numerous oil deposits, therefore, they have definitely passed that test over the past 500 million years, far surpassing the average sequestration timescales of other coastal blue carbon ecosystems.
Based on current science, there is every indication that kelp is a potentially important blue carbon ecosystem.