Lake Baikal giant amphipod crustaceans |
An exceptionnal concentration of species
It is notably thanks to its size (20% of the total surface liquid freshwater of the world and a depth of more than 1600m), age (at least 20 million years) and isolation of the lake Baikal that its amphipod crustaceans have developed an unprecedented adaptive radiation. Already 300 species have been described from the lake (totalling 20% of the world's freshwater species), 95% of them being endemic, and some Russian researchers speculate at least as many are still waiting to be discovered.
As their name
suggest, the Abyssogammarus (60mm)
species are limited to the deepest parts of the lake (never shallower than
300m).
Macrohectopus branicki, an aberrant planktonic
species, is the ecologic equivalent of the antarctic krill. Its huge swarms constitute more than 90% of the
amphipod biomass of the lake, and are the primary food resource of several
fishes of economic importance.
The key to polar gigantism
Moreover, Baikal amphipods are characterised by the world's most extensive size range. The adult size of these animals varies from 2 to 90 mm (compare with the maximum size of 37 mm of the Bitish species). The study of these organisms carried out at the Royal Belgian institute of Natural Sciences has resulted in a new hypothesis explaining polar gigantism, according to which the amount of dissolved oxygen determines the maximum potential size of these animals.
Pallasea cancellus is a big opportunistic species
(50mm). It adapts remarkably to captivity (more than 3 years at the
RBINS).
The wonderful
Acanthogammarus maximus (65mm)
belongs to the same genus than the biggest species both for the lake and the
world freshwater, measuring 90mm. It lives in shallow
water.
A rich collection
Two sucessive expeditions (1995; 1996) to lake Baikal have yielded more than 100 species belonging to 25 genera, ranking the Royal Belgian Institute of Natural Sciences' collections amongst the richest in the world, particularly with respect to the biggest species. It is also at our Institute that a handful of species have been studied in captivity, for the first time outside the ex-USSR.
Ommatogammarus albinus, which can be sampled by
thousands with baited traps up to the greatest depths of the lake show a
staggering ecological convergence with the numerous
necrophagous species of a marine amphipod superfamily, the lysianassoids.