Trees are the immediate mind association when people have to think about the natural ways in which carbon is stored or recycled. Whilst trees are a glorious, green form of natural carbon storage, there’s another that I’m even more fond of – Blue Carbon. Blue carbon refers to the removal of carbon dioxide from our atmosphere by our oceans and seas. In these ecosystems, organisms use carbon for their growth and it eventually ends up as the accumulation of organic matter on the seafloor. In fact, trees alone cannot account for all the carbon that is trapped globally. The big blue briny swell that covers about 70% of our planets’ surface is important here because the ocean contributes to approximately 83% of the global carbon cycle. The carbon cycle is the process by which carbon is exchanged within and between four key reservoirs: our atmosphere, our oceans, land, and fossil fuels. However, the role of the ocean as carbon sinks is relatively unrecognized – often, unless you’re already a bit of an marine advocate – like me!
Here, we take a look at some of the beautiful ways in which organisms in the ocean trap carbon:
Seagrasses
Of all the “green” carbon which is carbon that is fixed by photosynthetic activity, more than half (55%) of it is actually trapped by marine organisms such as seagrasses. Seagrasses form beautiful meadows in coastal ecosystems where they sequester (trap) more carbon per unit area than terrestrial forests. However, these ecosystems have been facing rapid decline and have lost approximately 30% of their historical global coverage. The key reasons for the loss of these fascinating meadows are the increase in coastal developments, dredging activities and decreases in water quality.
Photosynthesis in the Sea
Aside from seagrasses, there are plenty of other organisms in the sea that also trap carbon via photosynthesis. These include large seaweeds (macroalgae) like the ones you see in rockpools, along the water line of the beach and that form kelp forests. In addition to these, we also have microscopic algae (microalgae) such as the ones that DJ talked to us about and uses to design her clothing line. DJ takes carbon-trapping algae that originates from the sea and gives them a home on land, on us - through her clothing.
Jellyfish
A recent study has been receiving lots of attention as it discusses the role of gelatinous organisms in the global carbon cycle - yes, jellyfish can trap carbon too! The study reports that gelatinous organisms in the ocean such as jellyfish trap between 3.7 – 6.8 billion metric tons of organic carbon of which a substantial fraction reaches the seafloor. This amount is almost equivalent with the reported carbon emissions of the USA in 2018 (6.7), the second largest emitter globally. Jellies have typically not had great PR with their stinging abilities and strange texture but we at WSTP love to change the rhetoric for organisms that have not been held in good stead.
Mangroves and Marshes
Mangroves and coastal marshes are an important natural pathway of carbon storage. These ecosystems sequester 6 to 8 tons of CO₂ equivalent per hectare every year. These rates of carbon fixation are between 2 and 4 times greater than those observed in mature tropical forests. In fact, tidal marshes and mangroves play such a pivotal role in the carbon cycle that following the Paris Agreement, several nations included these ecosystems in their mitigation activities.
Scientists are increasingly sounding the alarm bells on the importance of Blue Carbon and how it can help us in our climate struggle. Simultaneously, seagrass and mangrove restoration projects are underway in many parts of the world and if you would like to help in citizen science projects, look no further! Scientists have created a seagrass mapping project to track and follow seagrass meadows through an app for your phone - seagrassspotter.org. This is a great way to help the oceans help us save the planet!