State of Marine and Coastal systems

4.4.1 Habitat fragmentation:  

Development which has occurred in response to human population growth has caused some parts of the coastal zone to suffer from reduced functionality. In some areas the coastal zone is on the verge of irreversible change, the coastal sectors closest to Durban in KwaZulu-Natal being a pertinent example. This area is extensively urbanised with development nodes around estuary mouths. Many of the catchments of these estuaries are planted to sugar cane which has led to accelerated sedimentation and eutrophication (Begg, 1978). Although the Estuarine Health Index (Cooper et al., 1995) includes an aesthetic component in an attempt to assess the impact of development on estuaries, it is not based on a clear set of measurable criteria that permit the assessment of development on the function of the estuarine environment. For State of the Environment assessments a more quantified approach is required that takes into account the degree and distribution of urbanisation around an estuary. Such an approach must permit comparisons within and between estuaries.

Bays along the South African coastline tend to serve as major nodes of urban development, e.g. Saldanha Bay, Table Bay, False Bay, Algoa Bay and Durban Bay. The greatest deterioration in environmental quality at these bays has occurred around the cities and major coastal towns.

Development at various other locations along the coast has resulted in the fragmentation of terrestrial ecosystems, particularly where development (resorts, for example) is spread linearly along the coast and is not concentrated. However, not all fragmentation effects are attributable to urban development: the coast of northern Namaqualand has been severely impacted by marine diamond mining.

The assessment of the state of estuaries of the Cape and Natal undertaken in1985/86 (Heydorn, 1986) has not been repeated. The Estuarine Health Index (Cooper et al., 1995) unfortunately does not provide data in a form that can be compared directly with the findings of the study by Heydorn. Nevertheless, the general perception of estuarine scientists is that the condition of many estuaries has deteriorated significantly in the past 15 years. The three most important factors contributing to the deterioration are: reduction in freshwater inflow; urban encroachment and uncontrolled exploitation of living resources, particularly bait organisms.

The National Water Act, Act 56 of 1998 requires a certain minimum amount of water to be left in the estuary for ecological purposes.Management classes must also be determined for each estuart. This management class is based on the present condition of the system and hence will provide the baseline for comparisons within and between estuaries.

4.4.2 Sea level rise:  

There are four stations recording sea level rise on the coast of southern Africa. These are located at Lüderitz (Namibia) and in South Africa at Port Nolloth, Simon's Town and Mossel Bay. Records at the first three stations indicate a positive trend in sea-level rise (relative to the land mass) over the past three decades (Figure 4.9). For example, the trend at Port Nolloth is a 12.3 mm rise per decade.

Figure 4.9 Trends in mean sea level

Since the west coast sea-level rise data are in agreement with the global trends, it is reasonable to accept that the predicted rates of sea level rise, modelled on the basis of global warming, are applicable to South Africa.

The Intergovernmental Panel on Climate Change has estimated that by the year 2030 global mean sea level will be 8-29 cm higher than in 1990, with a best estimate of 18 cm (Brundrit et al., 1995). A best estimate for the year 2070 stands at 44 cm. At present there are no apparent negative impacts of sea level rise.

4.4.3 Human health and well being: 

Many coastal bays are showing increased organic, nutrient, trace metal and hydrocarbon concentrations in the water. These changes present a risk to both human health and the marine ecosystem, for example, due to the accumulation of toxic trace metals in fish stocks from these areas. The results of various mussel watch programmes, which are co-ordinated by the Sea Fisheries Research Institute, show that trace metals are accumulating in mussels on the west coast. By comparison, changes to the environment as a result of other effluent discharges have been found to be surprisingly low and are generally limited to the immediate vicinity of the discharge.

4.4.4 Stocks of marine resources: 

Table 4.3 South African catches (tons nominal mass)
Table 4.4 Namibian catches (tons nominal mass)

Table 4.3 illustrates the pattern of fish harvesting per species in South African waters during the period from 1938 to 1997. The peak harvest is highlighted in bold. Trends indicating the levelling of stock are also apparent and are indicated in italics.

Demersal fish stocks quantified in Table 4.3 exhibit a stable pattern of resource harvesting throughout the time series. This can in part be attributed to the effective control and management of the fishery within South Africa's Exclusive Economic Zone. Pelagic stocks on the other hand are sensitive to prevailing environmental conditions e.g. El Niņo. The pilchard, anchovy and redeye exhibit a decreasing trend of catches over the years which is caused by over- fishing coupled with adverse environmental conditions. The great fluctuation in the anchovy catch is a feature of the species which reaches sexual maturity within the first year of its life.

Catch data for rock lobster indicate over exploitation of the stock in the early years (1938 to 1978). As a result, annual catches have decreased from 6930 tonnes in 1978 to 2582 tonnes in 1997.

Reasons for the general decrease in fish catches over the years include the improvement in fishing methods, increase in fishing effort and establishment of associated fishing industries in coastal towns and cities. A comparison can be made with Namibia's catches during the same period. A similar trend can be observed in the totals for demersal species (Table 4.3) although the actual figures are slightly lower than for South Africa. Pelagic fish catch figures are even lower for Namibia and this can be attributed to the unequal number of companies operating in the waters off the two countries. Fish catches in both countries appear to have levelled off in the last four years.

>     Marine and Coastal Systems: Impacts

There is also information about Terrestrial Ecosystems in the following reports:
Metropolitan reports:
	Cape Metropolitan Council (1998 edition)		Durban Pilot Study
	Greater Johannesburg Metropolitan Council (1999 edition)		Greater Pretoria Metropolitan Council (1999 edition)