Lake Victoria in east Africa was once home to hundreds of species of fish, but overfishing, low levels of oxygen in the water and the introduction of non-native fish, brought the lake to the verge of extinction. Unexpectedly though, several species have managed to survive. I’m Jim Metzner, and this is the Pulse of the Planet, presented by the American Museum of Natural History.
Ichthyologist Melanie Stiassny:
“There’s a small shrimp that’s always lived in Lake Victoria and nobody paid any attention to it. That shrimp is able to live with very low levels of oxygen. There’s another animal that’s able to cope with the loss of oxygen in Lake Victoria and it’s a small sardine. It can live way up in the surface waters where there’s always some oxygen.”
“Every once in a while, some of the de-oxygenated water will sweep up and it will engulf a whole shoal of sardines and they will suffocate. And the dead bodies of sardines fall to the bottom of the lake where the shrimp eat the sardine. Now that is the key to what’s keeping the whole system going.”
At the top of Lake Victoria’s current ecosystem, there is now one major predator — the Nile Perch — which was introduced into the lake some years ago and proceeded to devour practically all of the other native fish. The Perch now eat the shrimp; the shrimp eat the sardines, and if anything happens to any one of these species, the whole system collapses.
“And that’s one of the very important roles of biodiversity. It’s to give you that insurance policy. The pre-Perch system in Victoria was a buffered system. There were many different species. Changes could happen. You could have a virus that could affect maybe a hundred species, but the lake would still be OK because you had so many different players in the game. If you lose biodiversity and if you reduce a system to its bare bones, it’s very fragile.”
Pulse of the Planet is presented by the American Museum of Natural History. I’m Jim Metzner.