Blue carbon: The value of carbon sequestration in kelp forests compared to traditional blue carbon ecosystems

Since the term blue carbon was first coined in 2009, the interest in the carbon stocks and annual carbon sequestration of mangrove forests, salt marshes and seagrass meadows has increased noticeably. However, in the past couple of years, the carbon capabilities of kelp forests have also started to garner more attention, leading to multiple published studies arguing for their inclusion as a blue carbon ecosystem. However, so far, few studies have actually compared the amount of carbon stored and sequestered by kelp forests to the three traditional blue carbon ecosystems. Thus, the aim of this thesis was to estimate and compare the amount of carbon currently stored and annually sequestered by the different blue carbon ecosystems. Furthermore, the effects and costs of blue carbon ecosystem degradation were also estimated. Based on the results of a thorough literature review regarding the global distribution and degradation rates of the ecosystems as well as the amount of carbon sequestered and stored per unit area, the total amount of carbon stored in blue carbon ecosystems is estimated to be between 5 and 25 Pg, with mangrove forests storing roughly half of that. Yet, whilst kelp forests are estimated to have a far larger global distribution than all of the other blue carbon ecosystems combined, they only store around 0.1–1.4 Pg of carbon, since all of the carbon is stored in their biomass, unlike the other blue carbon ecosystems, in which the vast majority of carbon is located in the soils. However, the total amount of carbon sequestered annually by all blue carbon ecosystems is estimated to be between 40 and 331 Tg, out of which 8–231 Tg is sequestered by kelp forests. Yet, due to the degradation of the ecosystems during 2022, a combined 30–294 Tg of the previously stored carbon is estimated to be released into the atmosphere, whilst the amount sequestered during the year is reduced by roughly 0.4–6 Tg. Out of the carbon released, the majority is from the carbon stocks of seagrass meadows, whilst the carbon sequestration of kelp forests is reduced the most. The total combined cost of the degradation equals €9–174 billion, when the costs of the previously stored carbon released is combined with the NPV of the reduced carbon sequestration. Out of this, the total cost for kelp forests is estimated at €1–59 billion. However, whilst the number of studies published on blue carbon has increased, the data available regarding the ecosystems is still limited. As such, there are considerable uncertainties regarding the values presented and the results of the thesis should thus be considered rough estimates. That being said, the results still underline the importance of blue carbon ecosystems as carbon sinks as well as the considerable costs caused by environmental degradation. Furthermore, the thesis provides further support for the notion that kelp forests should indeed be considered a blue carbon ecosystem