1. ASSESSMENT OF SOIL ORGANIC CARBON STOCK IN SEAGRASS
BEDS OF GAZI BAY, KENYA.
Okoth Reagan1, Githaiga N. Michael2
1School of pure and Applied Science Kenyatta University, P.O Box 16778-80100,
Mombasa-Kenya.
E-mail: reaganokoth@hotmail.com
2Kenya Marine and Fisheries Research Institute, P.O Box 81651-80100, Mombasa-
Kenya.
Seagrasses are marine angiosperms inhabiting coastal areas from the intertidal zone
to several tens of meters deep in all the continents except Antarctica showing relatively
higher species diversity in the tropical regions than temperate. They provide important
ecosystem goods and services like sediment stabilization, provide habitat for marine
organisms and have also been recognized for their capacity to sequester and store
carbon in the sediment for a long time through the accumulation of autochthonous and
the allochthonous carbon. This study determines the organic carbon stock in the four
dominant seagrass species (Thalassodendron ciliatum, Syringodium isoetifolium,
Enhalus acoroides and Thalassia hemprichii) of Gazi Bay. Coring extending to 1m deep
was done within quadrats of 0.5m by 0.5m using a Russian peat sampling corer. The
cores were sliced into 5cm interval and taken to the laboratory for wet-dry weight
conversion. Sub-samples of 5g were analysed for organic matter (LOI). General
equations for the relationship between %LOI and %Corg in seagrass (%Corg=
0.43*%LOI-0.33) r2= 0.96 for seagrass soils with %LOI >0.2 and (Corg= -
0.21+0.40*%LOI) r2= 0.87 in seagrass soils with %LOI <0.2 were used to calculate
the Corg stock in each species. The study tested the differences in % organic matter for
vegetated and unvegetated sites, and the carbon stock among species using single
factor analysis of variance (ANOVA). In T. hemprichii, the % organic matter was
significantly different between the seagrass vegetated and the un-vegetated areas (F(1,
180) = 13.54; p =0.002) but not with depth in both the seagrass vegetated and un-
vegetated areas (F(9, 180) =0.85; p =0.567). In T. ciliatum, the % organic matter was
highly significantly different between the seagrass vegetated and the un-vegetated
areas (F (1, 180) = 123.84, p < 0.001) but was not statistically significantly different with
depth between the seagrass vegetated and unvegetated areas (F (9, 180) = 0.60; p =
0.794). In E. acoroides, the % organic matter was highly significantly different between
the seagrass vegetated and the un-vegetated areas (F (1, 180) = 13.54; p = 0.002) but
was not significantly different with depth between the seagrass vegetated and un-
vegetated areas (F (9, 180) = 1.01; p = 0.437. In S. isoetifolium, the % organic matter
was highly significantly different between the seagrass vegetated and the un-vegetated
areas (F (1, 180) = 179.62; p < 0.001) but was not significantly different with depth
between the seagrass vegetated and un- vegetated areas (F (9, 180) = 0.21; p = 0.983).

2. Sediment Corg was highly significantly different between species (F (3, 56) = 4.269,
p=0.005). The results of this study shows the important role of seagrass in climate
change mitigation and can therefore be used to advice current and future ecosystem
conservation planning.
Key words: Belowground carbon; REDD+; Seagrass; Kenya
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