Friday,21 September 2018, 1 : 37 PM

Lake Malawi

Nimbochromis Venustus
Nimbochromis Venustus
Image Credit: Hayath Mohammad

Introduction



lakeMalawi

Lake Malawi



Lake Malawi (Lake Nyasa, or Lago Niassa in Mozambique), is an African Great Lake and the southernmost lake in the East African Rift system, located between Malawi, Mozambique and Tanzania.


Location and Size

The lake lies in a valley formed by the opening of the East African Rift, where the African tectonic plate is being split into two pieces.
The lake is about 350 kilometers (220 mi) southeast of Lake Tanganyika, another of the great lakes of the East African Rift.

Lake Malawi is between 560-580 kilometers long, and about 75 kilometers wide at its widest point. The total surface area of the lake is about 29,600 square kilometers (11,400 sq mi). It is the third largest, second deepest lake in Africa, it is also the ninth largest in the world.



lakeMalawi as seen from space

Lake Malawi as seen from air

The lake has shorelines on western Mozambique, eastern Malawi, and southern Tanzania.
The largest river flowing into it is the Ruhuhu River, and there is an outlet at its southern end, the Shire River, a tributary that flows into the very large Zambezi River in Mozambique.


History of Lake

The age of lake is estimated to be in the range of 3-20 million years.
The substrate sediment is estimated to be about 4 km thick.
During its his troy the lake levels have dropped dramatically on various occasions.
It is said to much smaller about 25000 years ago and the water level was about 400 meter lower than the current level.
This level was maintained for a long time and was submerged later on, the echo sounding across entire lake.
The water level has risen substantially since then, also the sediment on the bottom have also risen.
These changes in lake size and depth are said to primary reasons for amazing diversity in this lake.
During lower levels the cichlids were able to move around, as the levels rose, the groups separated and evolved separately.


Names

The Portuguese trader Candido José da Costa Cardoso was the first European to visit the lake in 1846.
David Livingstone reached the lake in 1859, and naming it "Lake Nyasa".
David Livingstone's name for the lake was based on his colleague's misunderstanding of African languages of the area.
When Livingstone asked his staff members, who were not from the area of the lake, to state its name for him, they said the word "nyasa", not realizing that this was the local word for any large body of water such as a lake).
In effect, "Lake Nyasa" literally means "Lake Lake". T
This name could also be spelled "niassa", "nyanja", or "nyanza", based on the other languages of the region.

The geographic name of the lake is disputed.
Malawi claims that it is named "Lake Malawi", whereas other countries bordering on the lake, such as Mozambique and Tanzania, claim that the name is "Lake Nyasa".
The origin of the dispute over the name has its background in geopolitical disputes that began before the independence of Malawi was achieved in 1964, when the territory had been known as "Nyasaland".
For this same lake, the name "Lac Maravi" had been used on the map of "Afrique sud" by J.B.B. d'Anville, which was published in France in 1749.
The lake was also called "The Lake of Stars" by David Livingstone.
This name came about due to lights from the lanterns of the fishermen in Malawi on their boats, that resemble, from a distance, stars in the sky.
The lake is also known as the Lake of Storms, for the unpredictable and extremely violent gales that sweep through the area.



Water Temperature

Lake Malawi exists in tropical climate, due to this the surface temperatures do not vary much from deeper layers preventing any substantial vertical movement of water.
As there is not much vertical movement of water, the lower layers of lake do not receive oxygen.
Only the upper 200 m contain oxygen to support life.
The lower layers are colder and do not contain much life forms.

During dry seasons from June to August water from lower layers wells up lowering the surface temperature to nearly 20C.
In rainy season from November to April the temperatures rise to 30 C.
However the average surface temperature range from 23-28 C.

Water chemistry

The water in Lake Malawi or Nyasa is typically slightly alkaline with a pH ranging from 7.7 to 8.6.
General hardness (GH) 106 ppm and Carbonate hardness(KH) of 70 ppm.
The difference in ph ranges is mainly due to amount of Co2 in water.
In the surf zones the amount of Co2 is maximum resulting in lower ph values.


Fauna


lakeMalawi as seen from space

Lake Malawi Cichlids


Lake Malawi is reportedly the habitat of more species of fish than any other body of freshwater, including more than 1000 species of cichlids, and was officially declared a reserve by the Government of Mozambique.

Lake Malawi or Nyasa has for a very long time provided a major food source to the residents of its shores since its waters are rich in fish such as the chambo, consisting of any one of four species of the cichlid genus Nyasalapia, and the kampango, a large catfish (Bagrus meridionalis).

Some of the fish that are caught are exported from Malawi, but the wild population of fish is increasingly threatened by over fishing and water pollution.


Habitat

Lake Malawi is noted for being the site of evolutionary study among several groups of animals, most notably cichlid fish.
Several hundred endemic species are found in the lake, many of which have become popular among aquarium owners due to their bright colors.
Recreating a Lake Malawi/Nyasa biotopes to host cichlids became quite popular in the aquarium hobby.

The lake can be artificially divided into habitats as a convenient way to discuss cichlids, these habitats are not ironclad and species do cross between them but mostly remain in their preferred habitats.

These habitats are :

  • Wave-washed upper rocky habitat.
  • Sediment-free rocky habitat.
  • Deep sediment-rich rocky habitat.
  • Intermediate habitat (sand and rocks).
  • Shallow-Intermediate habitat.
  • Sheltered bay with aquatic plants.
  • Sandy habitat.
  • Deep waters cichlids

Out of total 1000 species of cichlids in the lake nearly 600 live in shallow waters, with the balance living offshore, the deeper parts may still contain species waiting to be discovered.
Cichlids live close to bottom and are referred as "Benthopelagic" (living close to bottom.), due to this they are found in shallow water, not in very deep water.
They also do not cross large open water bodies,this has resulted in their being restricted to their preferred locations.

The shore line of the lake has three distinct types:

  • The rocky areas,
  • sandy beaches
  • and swampy areas filled with reed found mainly where rivers and streams drain into the lake.

The cichlids of the lake are divided into two basic groups, loosely referred to as the haplochromine and the tilapiines.
Within the first group, Haplochromine, there are two subgroups.

The first one collectively called "Haps"consists of open water and sand dwelling species whose males display bright colors and whose females show a silvery coloration with sometimes irregular black bars or other markings. All haplochromines from Lake Malawi/Nyasa are mouth brooders.

The second subgroup is known both locally and popularly as mbuna, which means "rock dwellers".
The Mbuna species tend to be smaller, often specialized aufwuchs (hard algae) feeders, and often both sexes are brightly colored with males having several egg shaped gold spots on their anal fin.

The second group, the tilapiines, comprises the only substrate-spawning species in the lake (Tilapia rendalli), in addition to the four mouth brooding species of chambo (Nyasalapia).