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. The present 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, range: 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 presence 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 among 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.