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The seagrasses of Kenya and Tanzania
Ochieng, C.A.; Erftemeijer, P.L.A. (2003). The seagrasses of Kenya and Tanzania, in: Green, E.P. et al. (Ed.) World atlas of seagrasses. pp. 82-92
In: Green, E.P.; Short, F.T. (Ed.) (2003). World atlas of seagrasses. University of California Press: Berkeley. ISBN 0 520 24047 2. XII, 298, maps, colour plates pp., more

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  • Ochieng, C.A.
  • Erftemeijer, P.L.A.

Abstract
    Seagrasses are a major component of the rich and productive coastal and marine ecosystems in the East African region. The Kenyan (600 km) and Tanzanian (800 km) coastlines have a shallow and relatively narrow continental shelf bordering the Indian Ocean and are characterized by extensive fringing coral reefs, several sheltered bays and creeks, limestone cliffs, mangrove forests, sand dunes and beaches. The tidal amplitude is rather large – up to 4 m near Mombasa – and therefore there is a fairly extensive intertidal zone between the fringing reefs and the coast in many places. The substrate in this zone consists mainly of carbonate sands derived from eroding reefs. The productivity of these intertidal areas is determined predominantly by the presence of seagrasses and macroalgae, which grow wherever shallow depressions retain a covering of water during low tide. The most extensive seagrass meadows occur in back-reef lagoons, which are found between the beaches or cliffs and the adjacent fringing reefs. Narrow channels connect the lagoons with the sea during the low tide, but high-tide waters pass over the reef crest into the lagoon. Apart from many fish species that reside permanently inside such lagoons, many other species feed there during high tide, leaving for deeper offshore waters during ebbing tides. At several places along the East African coast, these lagoons grade into sheltered semi-enclosed bays (e.g. at Mida, Kilifi, Mtwapa, Tudor, Gazi and Funzi in Kenya and at Tanga, Bagamoyo, Mohoro, Kilwa and Mtwara in Tanzania) where mangroves, seagrass meadows and coral reefs occur as adjacent and interrelated ecosystems. Where the supply of terrigenous sediments is limited, seagrass vegetation is also common in the creeks and channels that run through the mangroves, possibly functioning as traps and reducing the extent of the fluxes of particulate matter and nutrients between the mangroves and the ocean. In Gazi Bay (Kenya), for example, it is possible to snorkel in creeks and small rivers inside the mangroves, where the water is very clear and the bottom is covered in a luxurious growth of seagrasses. In the Delta areas of major rivers, such as the Tana River in Kenya and the Rifiji River in Tanzania, seagrass growth is minimal.

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