The main problems and their causes

It is perhaps ironic that the problems of the coastal zone and ocean in Sub-Saharan Africa derive from their usefulness and in particular from the settlement of humans on or near the coast.

The open ocean, however, seems as yet to be largely unaffected by either the environmental degradation wrought by humans or the overexploitation of its natural resources. For living resources in the open ocean, the only danger signal comes not from the activities of coastal states but from foreign fleets (from Japan, South Korea, Taiwan, and the former USSR, among others), which "poach" fish from these waters. For example, tuna in the western Indian Ocean (eastern Africa) is heavily exploited by these foreign fleets and recent indications are that yellow and southern blue fin tuna and bill fish are overexploited and that bigeye tuna and albacore are fully exploited (Ardill 1984). Bryceson et al. (1990) stated that this fishing pressure with highly sophisticated gear has an adverse impact on smaller-scale operations conducted by the fishing fleets of the region, and that artisanal fishermen have noticed marked decreases in catches of large pelagic migratory species.

On the Atlantic coast of Africa, similar pressures exerted by foreign fishing fleets have produced similar consequences (e.g. depletion of deep water prawn/shrimp resources) for the local fishing industry (Ajayi, personal communication).

Besides the operations of foreign fishing fleets, which are sometimes illegal, many of the fisheries of the region are artisanal and based mainly in the coastal zone. Here population pressures have increased consumption and demands and led to the use of destructive fishing methods.

In the coastal zone of eastern Africa, the most environmentally destructive method of fishing is dynamite blasting, mostly associated with coral reef habitats. Bryceson (1978a) reported that repeated blasting over a long period of time has meant the destruction of extensive areas of coral reef and the decline of their fisheries' productivity. The livelihood of artisanal fishermen who employ more traditional methods is threatened. Bryceson (1978a) also reported that spear-fishing had been banned in most countries of the region owing to its damaging effects on reefs and on populations of particularly vulnerable species. For the same region, Kayambo (1988) points out that depletion of the mollusc population as a result of its intensive collection for export and sale to tourists has been a cause for concern.

In the coastal zone of western Africa, in response to increasing demands for fish and fish products, trawling now prevails in areas formerly dominated by traditional fishermen. However, these operations are largely unregulated (or do not conform to regulations where they exist), with incorrect mesh sizes resulting in destructive fishing, including the catching of undersized fish (Ajayi, personal communication).

It is, perhaps, pertinent to mention that on the eastern and western coasts of Sub-Saharan Africa, the potential for aquaculture development is great and people are being urged to take it up as a way of increasing overall fish production. However, experience from its limited practice shows that the potential for environmental degradation (e.g. associated with clearing mangroves) is also great.

Mining of sand (siliceous and calcareous), gravel, and other construction materials (e.g. Iimestone) from estuaries, beaches, or the nearshore continental shelf is common (Ibe 1982, 1987a,b; lbe and Quelennec 1989) in the coastal states and islands of Sub-Saharan Africa. The mining of sand and gravel from coastal rivers and particularly from estuaries tends to diminish the amount of fluvial sediment input to the coastline, thereby accelerating shoreline retreat. Sand extraction directly from beaches seriously depletes the sediment pool available, and beach retreat is either induced or accelerated. Dredging of sand from the inner continental shelf is an obvious cause of beach erosion in Africa. This is because the beaches along these coasts exist in dynamic equilibrium with the nearshore continental shelf. Therefore, dredging of sand/gravel for replenishment, land reclamation, or other civil engineering construction from the shore area or, for that matter, anywhere else within the dynamic system inevitably disrupts this equilibrium and enhances shoreline retreat. Countries where this problem has been documented include Liberia, Sierra Leone, Cote d'Ivoire, Nigeria, Mauritius, Tanzania, Kenya, the Seychelles, and Mozambique (Ibe et al. 1983; Ibe 1986c; Ibe and Quelennec 1989; Bryceson et al. 1990).

Besides the increased threat of erosion, the mining of construction materials from the coastal zone has a tendency to disrupt fragile ecosystems such as coral reefs and mangroves and affect their productivity (Ibe 1982; Ibe et al. 1985).

Lead-silver ores were quarried in Kinangoni, Kenya, and were a cause for concern as regards metal pollution, so that the quarries had to be closed (Muslim 1984).

The exploration, exploitation, refining, and transportation of oil and gas in Sub-Saharan Africa, although contributing to economic development, bring worrying problems because these activities routinely contribute a variety of pollutants to the coastal zone and oceans. These include hydrocarbons from occasional spills but, perhaps more importantly, from chronic low-level releases associated with leaking valves, corroded pipelines, ballast water discharges, and production water effluents. Drilling fluids contain diesel and some toxic chemicals that cause pollution. Heavy metals, particularly vanadium and nickel, are introduced through oil-field operations and are known to affect life forms.

Another impact of oil production is the initiation or exacerbation of subsidence in the fragile coastal zone. The main effect of fluid extraction is the reduction of fluid pressure in the reservoir, thus leading directly to an increase in the "effective stress" (or grain to grain stress) in the system. Compaction results and the sedimentary basin subsides (Cooke and Doornkamp 1974). The subsequent progressive inundation of the coastline results in accentuated erosion. Ibe et al. have documented this phenomenon in Nigeria's oilproducing Niger delta (Ibe et al. 1985; Ibe 1988b).

In oil-producing coastal states, a network of canals for hydrocarbon exploitation and transportation, on or near the coast, constitutes a visible structural modification of the coastal zone that has adverse effects on coastline migration.

As stated elsewhere, perhaps the greatest problem in the coastal zone arises from development activities linked with coastal settlements. Coastal towns are by far the most developed in Sub-Saharan Africa and, by implication, the location of residential, industrial, commercial (including harbour and port construction), agricultural, educational, and military facilities in the coastal zone is high (Ibe 1988a, 1989). The increasing awareness of the revenue-generating potential of tourism has also led to increased construction of tourist facilities on beaches along the coast. Construction activities in the coastal zone loosen the sediment binding by removing the surface revetments and increasing rainwater runoff. Thus soil erosion is enhanced. On the other hand, structures constructed on the coast, by strengthening the soil, may lead to decreased sediment supply to the shoreline. The opposite problems of increased siltation and sediment starvation along the coast result, depending on the local physiographic conditions.

The pollution caused by these settlements and the accompanying development activities threatens to make nonsense of the concept of sustainable development. The pollution results primarily from raw or insufficiently treated domestic sewage and from untreated toxic and deleterious wastes from industries, which generally discharge directly into rivers, estuaries, and the nearshore ocean. Preliminary results from pollution-monitoring projects instituted by United Nations agencies, including the Intergovernmental Oceanographic Commission of UNESCO in Eastern and Western Africa, show that pollution by pathogenic organisms, pesticides, chemical fertilizers, and petroleum hydrocarbons is widespread, while metal pollution occurs as hot spots close to industrial sites.

Solid matter (litter) from industries, households, shipping, and the tourist trade poses a problem of an unsightly and irritating nature, but it also has serious public health implications.

The construction of ports, harbours, and piers for national and international trade has a direct negative impact on the environment. This is because, for the most part, these structures lie perpendicular, or nearly so, to the littoral zone, thereby causing acute down-drift erosion. This problem has been documented in Benin, Togo, Nigeria, Liberia, Ghana, Cote d'Ivoire, South Africa, Tanzania, and Somalia, among others. In most of these cases, attempts at solving the harbour-induced erosion have further exacerbated the problem (Ibe 1986a,b).

Increased clearing of coastal vegetation at construction and mining locations or for the establishment of agricultural farms or the expansion of settlements leads to increased surface runoff and makes the exposed area extremely vulnerable to mass movement and to erosion by winds, currents, and water. Large areas of mangroves have been cleared in Kenya, Tanzania, Ghana, and Mozambique for the production of salt by evaporation (Ibe 1987a; Semesi 1988). In Mauritania, Guinea, Sierra Leone, Liberia, Togo, and Angola, open peat mining in littoral zones also contributes to the destruction of vegetation and the acceleration of coastal erosion. The clearance of mangroves is particularly serious because mangroves, in addition to serving as windbreaks, provide excellent spawning and nursery grounds for a variety of coastal organisms, including fish, crustaceans, and molluscs. The loss of mangroves therefore has serious implications for the productivity of coastal ecosystems.

An additional possible problem in coastal areas relates to the expected effects of global warming on shallow ocean and coastal zones, in particular the impact of the associated rise in sealevel. The negative implications of global warming, if they occur, will be considerable for natural and man-made ecosystems, human and animal health, and the spatial and temporal characteristics of natural and human resources (Ibe 1989; Ibe and Ojo 1993; Ojo 1992; Tobor and Ibe 1992).