Carbon storage in the seagrass meadows of Gazi Bay, Kenya

Vegetated marine habitats are globally important carbon sinks, making a significant contribution towards mitigating climate change, and they provide a wide range of other ecosystem services. However, large gaps in knowledge remain, particularly for seagrass meadows in Africa. This study estimated biomass and sediment organic carbon (C_org) stocks of four dominant seagrass species in Gazi Bay, Kenya. It compared sediment C_org between seagrass areas in vegetated and un-vegetated ‘controls’, using the naturally patchy occurence of seagrass at this site to test the impacts of seagrass growth on sediment C_org. It also explored relationships between the sediment and above-ground C_org as well as between the total biomass and above-ground parameters. Sediment C_org was significantly different between species, and ranged from 160.7 – 233.8 Mg C ha^-1 (compared to the global range of 115.3 to 829.2 Mg C ha^-1). Vegetated areas in all species had significantly higher sediment C_org compared with un-vegetated controls; the prescence of seagrass increased C_org by 4-6 times. Biomass carbon differed significantly between species with means ranging between 4.8 – 7.1 Mg C ha^-1 compared to the global range of 2.5 – 7.3 Mg C ha^-1. To our knowledge these are the first results on seagrass sediment C_org to be reported from African seagrass beds; and contribute towards our understanding of the role of seagrass in global carbon dynamics.