Lake Baikal is the largest body of freshwater in the world. It holds nearly 1/4th of all freshwater on Earth, it holds the water for a long time, a very long time. Waters enters the lake from the south, from Mongolia, and stays or resides in the lake for over 300 years and the lake itself is ancient, over 20 million years old, by our best estimates. The length of its shoreline is about the distance from New York City to Miami, Florida and it is a long lake, a narrow lake at about 400 miles long and 50 miles wide. The large volume of the lake does not arise from its great length or width, but rather from its great depth.
And it is deep, close to a mile deep in its deepest reaches. Down in that deep, dark, cold environment lives a midge with the impressive name of Sergentia. Sergentia flavodentata so named by Chernovskij has been found in its immature larval stage from the depths of Lake Baikal. The larvae of this midge mine the soft, nutrient-rich sediments at the bottom of this lake in total darkness, perhaps for two years.
Eventually the larvae metamorphosize into pupae and begin the long slow swim, swimming up through thousands of feet (or meters) to the surface of this lake. The pupae flip their bodies up and down to produce a swimming motion. Now think about this, a small Sergentia pupa, less than an inch in length, maybe one to two centimeters long, must rise this great distance. Imagine an inch worm inching along the roadway for about a mile. That is a formidable distance. The pupae must accomplish this feat through water currents while avoiding predators such as fish, to get to the surface of the lake.
Once on the surface of the lake, the impossible begins. The adults, males and females, must find each other in the wave-chaos surface of an immense lake. This lake shown here. They mate and the female lays the eggs, she oviposits the eggs on the surface of the lake and the eggs slowly, so slowly settle down the the bottom, thousands of feet below.
This wonderful and unique midge is not known to the world at large. This amazing, huge, and ancient lake is not well known outside of Russia and outside of the aquatic ecology community. Just a bit of brain candy from Tethysphere.
For more reading:
Kravtsova, L.S., Bukin, Y.S., Peretolchina, T.E. and Shcherbakov, D.Y., 2015. Genetic differentiation of populations of Baikal endemic Sergentia baicalensis Tshern.(Diptera, Chironomidae). Russian journal of genetics, 51(7), pp.707-710.
Linevich AA (1971) The Chironomidae of Lake Baikal. Limnologica
Wetzel RG (2001) Limnology, lake and river ecosystems. Academic
Press, New York
The photo image of Lake Baikal was retrieved from Wikipedia: https://en.wikipedia.org/wiki/Lake_Baikal and it is free to share.