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The Role of Intertidal Macrophytes on Sediment and Coastal Stabilization at Bofa Beach, Kilifi – Kenya.
Randall MABWA1, Bernerd FULANDA2, 1 Department of Biological Sciences, 2 School of Pure and Applied Sciences; Pwani University, Kenya
Results
Conclusion-‐ The study’s results support the hypothesis; Intertidal macrophytes have a significant influence on sediment stability.
-‐ High erosion rates were noted in low cover areas comparative to the low rates in highly covered areas.
-‐ The role in sediment and coastal stabilization is evident due to the positive impact of leaf height in settling sediments (deposition). Leaf width aids in reducing resuspension of sediments and further reducing/ preventing erosion; hence stabilizing the intertidal area and coastline.
-‐ It is imperative that intertidal macrophytes not be overlooked in ecosystem management efforts with respect to stabilizing intertidal zones.
-‐ Future research focusing on a single macrophyte species would be essential to prove the role clearly.
-‐ It is possible to adopt the use of effective macrophytes in intertidal erosion management. This is essential to:
1. The conservation of beaches and their natural profiles.
2. Adopting seawall design that considers sediment and flora -‐ role interactions.
-‐ A positive influence between leaf height and deposition (r2 = 0.7378) was noted; Thalassia hemprichii and Thalassodendron cilitium had greater influence on sediment deposition.
-‐ The lowest influence was noted in Macro algae (Chlorophyta)
-‐ At r2= 0.4066, leaf width had a comparatively lesser influence on sediment deposition than leaf height.
-‐ Increase in leaf width led to a reduction in erosion by species despite a lesser coefficient of correlation (r2= 0.4643); lesser coefficient is due to use of multiple species as compared to one specie in the study.
-‐ There was minimal to no relationship between leaf height and reduction of erosion (r2=0.0086)
• 7 macrophytic species were identified; 5 in seagrass families while 2 comprised macroalgae.
• Thalassia hemprichii was most the dominant followed by Syringodium isoetifolium, Cymodocea rotundata,
Thalassodendron cilitium, ENS value-‐ 4.7 (the exponent of the Shannon wiener index value; 1.546).
• There was variable habitat characterization; seagrass, sand, coral; macroalgae and coral with variable cover along
percentage ranges. (100% to less than 40%).
• A correlation test of erosion and deposition rates by leaf size (leaf height and leaf width).
Introduction
• The study site was located at the Bofa beach, north of the Kilifi creek; -‐3.633⁰ S 39.850⁰ E, straddling over 1.5km of
the intertidal area. The area is characterized by a steep descent with sandy, coral reef flats at the intertidal areas;
sedges on the terrestrial side.
Methodology• A 1.5km transect was divided into 3 sites with 10 stations each, with Sampling occurring from January to April 2017,twice weekly during low Neap and Spring tide periods.
• Calibrated plastic cups were attached to pegged poles; An empty one at a height of 10cm for sediment collectionand one filled with sand to the brim to measure erosion at ground level twice during the sampling day.
• Species data was sampled via use of a 1m2 string quadrat and all macrophytes classified up to the lowest levelpossible.
• The leaf blade width (mm) and leaf height (mm) measurements; (denoting leaf size) were recorded via use ofVernier calipers.
• Correlation between the leaf size and erosion/ deposition rates was determined and an inference made.
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Chlorophyta
Thalassodendron cilitium
Syringodium isoetifolium
Cymodocea rotundata
Thalassia hemprichii
Halophila ovalis
Phaeophyta
Leaf Height and Width versus Deposition and Erosion
Habitat Characterization