Marine biodiversity in Nigeria – the known and the unknown
Nigeria has a coastline of 853 km, a maritime area of 46,500 km2 and an exclusive economic zone of 210,900 km2. The Nigerian coastal area is hot and humid, with an annual temperature range between 26 and 34oC, and the highest temperatures occurring during the dry season (November to March). The total annual rainfall averages between 350 and 600 centimeters. More than 80 percent of the rain falls during the rainy season (April to October) when tropical storm conditions are frequent. Rainfall is usually heavy and occasionally lasts for over 24 hours. Rainfall of about 50mm/hour between July and August are common and results in flash floods. The predominant wind is the rain bearing southwest trade wind from the Atlantic Ocean. During the short dry period, the dust laden north east dry wind from the Sahara desert reaches the coastal areas, producing hazy conditions (Ibe et al. 1985). The Nigerian intertidal mangrove swamps cover an area of about 5,590 square kilometres (Allen 1965). The swamps are separated from the sea by barrier-bar islands that are usually broken by tidal channels. The Niger delta area, which has a flourishing mangrove ecosystem, was formed by long and continuous interactions of sediment laden Niger River water and coastal processes, creating beach-ridges, barrier islands, a fresh water floodplain and brackish mangrove swamp. This coastal habitat is interrupted by a series of estuaries, lagoons and embayments. The total brackish water habitat is estimated as 12,900 km2. The mangroves, wetlands and inter-tidal systems occur in saline soil subject to tidal inundation and occupy a total area of almost 1 million hectares (Okigbo 1984, FAO 1981). Fishing is the main occupation of the coastal communities, with various types of gears being employed. Fishing is conducted in creeks, rivers, estuaries, mudflats, near-shore and offshore. Commercial fishing supports about 440 trawlers, with about three quarters of the fleet targeting the shrimp resources. The mangrove plants and associated halophytic plants are used for building, extraction of tannin; construction works, curing of fish, and other fishing implements. Mineral resources in the coastal and marine waters include petroleum, with an oil reserve of about 21 billion barrels and gas reserve estimated at more than 11 trillion cubic feet. Current production levels are at about 1.9 million barrels of crude oil and 200,000 barrels of gas condensate per day. The current natural gas production is 3,400 million cubic feet per day in the form of associated gas, of which about 340 million is marketed in the domestic market, 340 million re-injected and 2,720 million cubic feet is flared daily. Sand and gravel are exploited onshore and offshore, in the riverbed, lagoons, estuaries and beaches. Millions of cubic meters of sand are dredged annually during oil exploration and exploitation, as well as for the construction industry. Most of the sand mined is used for reclamation of swampy areas, in the block-making industry and construction work.