Abstract
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 (Corg) stocks of four dominant seagrass species in Gazi Bay, Kenya. It compared sediment Corg 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 Corg. It also explored relationships between the sediment and above-ground Corg, as well as between the total biomass and above-ground parameters. Sediment Corg 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 Corg compared with un-vegetated controls; the presence of seagrass increased Corg 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 Corg to be reported from African seagrass beds; and contribute towards our understanding of the role of seagrass in global carbon dynamics.
Highlights
Carbon sinks in terrestrial ecosystems are better studied than those in marine plant communities
The sediment Corg varied between meadows of different species with the highest being recorded in E. acoroides at 295.7 ± 63.6 Mg C ha-1 and the lowest in S. isoetifolium at 160.7 ± 40.3 Mg C ha-1 (Fig 3)
The current study investigated biomass and sediment Corg stocks associated with the four dominant seagrass species of Gazi Bay, providing amongst the first data from Africa for seagrass sediment Corg [40]
Summary
Carbon sinks in terrestrial ecosystems are better studied than those in marine plant communities. The global importance of vegetated coastal habitats as carbon sinks has become appreciated over the last decade [1] These ‘blue carbon’ ecosystems (tidal marshes, mangroves and seagrass meadows) have recently been demonstrated to capture and store huge stocks of carbon, and their management and conservation may play an important part in global climate change mitigation strategies [2,3,4,5]. They occupy less than 2% of the world’s ocean surface area [6], blue carbon ecosystems are estimated to bury nearly 27.4 Tg C yr-1 which is about 10% of the yearly estimated organic carbon (Corg) burial in the oceans [7]. Unlike many terrestrial systems that store Corg primarily in living biomass, vegetated coastal ecosystems store much of their Corg stock in the sediment, which may produce carbon sinks of hundreds
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