extend along much of the coast, extending.5 to 2 km from the shore on the narrow continental shelf. Fringing reefs extend along the coasts of Kenya and Tanzania as far as the Ruvuma River, which forms the Tanzania-Mozambique boundary. The fringing reefs are interrupted by major river mouths, including the Tana and Athi rivers in Kenya and the Rufiji in Tanzania. Unguja Island has a fringing reef along its eastern shore and extending around the southern and northern tips of the island. Mafia Island has a fringing reef along its eastern shore which extends south to the Songo Songo Islands. Seagrass beds are found in clear, shallow lagoons between the fringing reefs and the shore, and between offshore islands and the mainland. River mouths are home to the East African mangroves. The Rufiji River delta is the largest mangrove ecosystem on the East African coast, and accounts for half of Tanzania's 55,000 ha of mangroves. Other important mangrove forests in Tanzania are at Mwanza and Tanga, at the mouths of the Wami, Ruvu, Matandu and Ruvuma rivers, and on the islands of Mbegani, Kunduchi, Latham, Kisiju, Kivinje, Urguja, Kilwa, and Mafia. Kenya has 52,980 ha of mangroves, over two-thirds of which are concentrated around Lamu. Kilifi and Kwale account for most of the rest. Fringing reefs are uncommon along the Mozambican coast, limited by freshwater input from numerous rivers, and cold-water upwelling in the Mozambique Channel. Patch reefs are best developed on the Quirimbas Islands, Primeiras and Segundas Archipelago, and Mozambique Island and neighboring islands in Mozambique Bay. Mangroves are found in the many river mouths, and seagrass beds occur in sheltered coastal waters.
The reefs provide many food fishes for coastal communities, including grunts, snapper, and parrotfish. Spiny lobsters – chiefly Palinurus ornatus, and also P. versicolor and P. longipes, are the most lucrative. Coastal tourism is growing in economic importance in Kenya and Tanzania.
Threats
The reefs, seagrass beds, and mangroves are increasingly threatened by human activity. Soil erosion from agriculture and grazing has increased the amount of silt carried by rivers into the coastal waters, damaging reefs and seagrass beds. Rivers also transport chemical fertilizers and toxic pesticides into marine environment. Over-fishing and exploitation of seashells, corals, turtle shells, for tourist souvenirs are diminishing marine fauna. Reefs are being destroyed by dynamite fishing, and mining of coral reefs for lime and construction materials. Bottom trawling for fish damages seagrass beds.
