Abstract:
Seagrass beds occur globally in both intertidal and subtidal zones within shallow marine
environments, such as bays and estuaries. These important ecosystems support fisheries production,
attenuate strong wave energies, support human livelihoods and sequester large amounts of CO2
that may help mitigate the effects of climate change. At present, there is increased global interest
in understanding how these ecosystems could help alleviate the challenges likely to face humanity
and the environment into the future. Unlike other blue carbon ecosystems, i.e., mangroves and
saltmarshes, seagrasses are less understood, especially regarding their contribution to the carbon
dynamics. This is particularly true in regions with less attention and limited resources. Paucity
of information is even more relevant for the subtidal meadows that are less accessible. In Kenya,
much of the available information on seagrasses comes from Gazi Bay, where the focus has been
on the extensive intertidal meadows. As is the case with other regions, there remains a paucity
of information on subtidal meadows. This limits our understanding of the overall contribution of
seagrasses in carbon capture and storage. This study provides the first assessment of the species
composition and variation in carbon storage capacity of subtidal seagrass meadows within Gazi
Bay. Nine seagrass species, comprising of Cymodocea rotundata, Cymodocea serrulata, Enhalus acoroides,
Halodule uninervis, Halophila ovalis, Halophila stipulacea, Syringodium isoetifolium, Thalassia hemprichii,
and Thalassodendron ciliatum, were found. Organic carbon stocks varied between species and pools,
with the mean below ground vegetation carbon (bgc) stocks (5.1 ± 0.7 Mg C ha−1
) being more than
three times greater than above ground carbon (agc) stocks (0.5 ± 0.1 Mg C ha−1
). Mean sediment
organic carbon stock (sed Corg) of the subtidal seagrass beds was 113 ± 8 Mg C ha−1
. Combining
this new knowledge with existing data from the intertidal and mangrove fringed areas, we estimate
the total seagrass ecosystem organic carbon stocks in the bay to be 196,721 Mg C, with the intertidal
seagrasses storing about 119,790 Mg C (61%), followed by the subtidal seagrasses 55,742 Mg C
(28%) and seagrasses in the mangrove fringed creeks storing 21,189 Mg C (11%). These findings are
important in highlighting the need to protect subtidal seagrass meadows and for building a national
and global data base on seagrass contribution to global carbon dynamics.
