Q: What’s more than a mile deep, 400 miles long, and holds 20% of all of the Earth’s fresh surface water?
A: Lake Baikal, which is a huge body of water located in a remote corner of southeastern Siberia, just above Mongolia. The deepest lake in the world and the largest freshwater lake by volume, Lake Baikal is so interesting that it was named a UNESCO World Heritage Site in 1996. UNESCO chose well; the geology and biodiversity of Lake Baikal are truly unique.
The age and isolation of Lake Baikal combine to make it quite unusual. As described by John Langdon Brooks in the Quarterly Review of Biology, Lake Baikal has an “extraordinarily high degree of endemism,” meaning hundreds of species there are found nowhere else on Earth. This concentration of unique species extends up and down the food web; while the fish are for the most part not unique, there are hundreds of species of small invertebrates in the lake found nowhere else on Earth. There are even six species of unique freshwater sponge. And at the top of the food web is the Baikal Seal, the only species of seal in the world that lives exclusively in freshwater.
The nature of the lake itself lends it to great diversity. For one thing the lake is at least 25 million years old. It is also extremely deep, and unlike many deep lakes, all depths contain plenty of dissolved oxygen. Under such conditions, organisms have the entire lake in which to speciate. Species can differentiate at opposite ends of the lake, or in the same location but at different depths. Several river systems drain into Baikal, so additional organisms have the opportunity to colonize the lake. Some of these species remain as they are, adding to the diversity, while others evolve in the lake into even more unique creatures.
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