Biodiversity and Conservation

Inland water bodies are generally patchy with respect to habitats lying within each catchments area. Recent mitochondrial studies have shown that each habitat, even within a range of 700 m, may be an island with endemic species arising through allopatric and sym-patric speciation. The characterization of species and species complexes in African lakes is a challenge but also provide a living laboratory for scientists. Thus conservation of species flocks to uphold variation is tied to maintaining ecosystem integrity. In turn, this important for sustenance of rural livelihoods that depend on fishing. Some of the unique ecosystems have been designated heritage sites led, among fresh-waters, by the establishment of the Lake Malawi National Park in 1982 and its subsequent attainment of status as a World Heritage Site. These sites have particular value to science and will serve future generations.

The inability of cichlid to cross valleys is exemplified by the proliferation of Pseudotropheus species and/or subspecies in Lakes Tanganyika and Malawi. It is contended that this might have contributed to species radiation, coupled with lake level changes.

Table 1 Diversity of physical and chemical characteristics of selected sub-Saharan African Lakes

African Great Lakes and other lakes

Table 1 Diversity of physical and chemical characteristics of selected sub-Saharan African Lakes

African Great Lakes and other lakes

Parameter

Lake

Lake

Lake

Lake

Lake

Lake

Lake

Lake

Lake

Chad

Chilwa

Kivu

Albert

Turkana

Edward

Victoria

Tanganyika

Nyassa/ Malawi

Surface area

2000-

1858

2700

5300

6750

2325

68 800

32600

29 500

(km2)

22 000

Max. Depth (m)

9.5

2.1

240

58

109

112

79

1470

700

Mean depth

3.9

220

25

30.2

17

40

580

264

(m)

Volume (km3)

75

-

500

280

203.6

912

2760

18 900

7775

Drainage area

2.5 x

1160

7000

-

130 860

12 096

195 000

220000

100 500

(km2)

106

Altitude (m.asl)

1463

622

1500

615

360

-

1134

774

474

River inflow

-

-

-

20

14

29

(km3 year-1)

River outflow

-

-

-

20

2.7

12

(km3 year-1)

Rainfall

-

<250

-

100

29

39

(mm year-1)

Evaporation

1757

-

2335

-

100

50

57

(mm year-1)

Residence

-

-

12.5

-

23

440

114

time

(years)

Na+ (mmol l-1)

0.5

189-780

5.70

3.96

4.78

450

2700

840

K+ (mmol l-1)

0.2

3.7-23.8

2.17

1.67

2.32

97

820

150

Ca2+ (mmol l-1)

0.8

7.0-18

1.06

0.49

0.57

140

270

450

Mg2+ (mg l-1)

0.3

5.2-8.6

7.00

2.69

3.98

110

1650

300

Cl-1 (mg l-1)

0.0

182-515

0.89

0.94

1.03

110

750

100

SO2- (mg l -1)

0.005

-

0.33

0.76

0.89

<24

37

30

Alkalinity

0.11

6.7-19

16.4

7.33

9.85

0.92

6.52

2.3

(mg l-1)

Conductivity

180

800-2500

1240

735

3300

925

97

610

230

(mS cm-1)

pH

8.0-8.5

7.6-9.5

9.1-9.5

8.9-9.5

9.5-10.5

8.8-9.1

7.1-8.5

8.0-9.0

Cations

1.8

15.93

8.81

11.65

1.02

7.46

2.46

Anions

1.9

17.62

9.03

11.77

1.05

7.62

2.59

Figure 4 The major climatic zones of tropical Africa (modified from Walter et al., 1975).

The subtropical dry zone The tropical summer-rainfall zone

Tropic of Capricorn

Figure 4 The major climatic zones of tropical Africa (modified from Walter et al., 1975).

The subtropical dry zone The tropical summer-rainfall zone

Tropic of Capricorn

Existing as either relics of a large body of water contracted by siltation and other changes in the earth crust, as is the case with Lake Chad or by uplifting of the Earth's crust as in Lake Victoria, there is a large diversity of lakes. Some of the lakes have become internal drainage systems that undergo fluctuating salt changes during periods of drying and refilling, as is the case with Lakes Chala, Chilwa, Nakuru, Magadi or Turkana among the larger forms and Mombolo, Rombou or Latir of the smaller lakes.

Spatial and temporal structural heterogeneity of lake habitats is a major ecological factor influencing the existence and sustainability of aquatic ecosystems in Africa. As a result, there is a relatively high proportion of endemism among fish species, which have evolved independently in the different freshwater systems in Africa.

While the African Great Lakes harbor diverse and unique flora and fauna, it is the high endemism in fish species that attracted most interest. Among the Great Lakes, Lake Malawi has the most species exceeding 850, nearly all of them being endemic, despite the fact that it is of more recent origin than Lake Tanganyika.

It is generally accepted that reported numbers are an underestimate and 11 families have been identified with Cichlidae being the most speciose. The Lake Tanganyika fauna is less speciose, with a total of 16 families and more than 200 cichlid species. Lake Victoria is estimated to have been inhabited by more than 500 species, which have since declined, some becoming completely extinct through predation and competition from introduced Nile perch (Lates nilo-ticus) and Oreochromis niloticus, respectively. The introduction of Lates niloticus and Oreochromis niloticus into Lake Victoria has led to the disappearance of more than 200 endemic species within a relatively short space of time of ten years. Arguably, this represents the greatest demise of the vertebrate group recorded in modern times.

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