A Tectonic Lake of Unique Life
Lake Poso is an ancient tectonic lake, formed by movements of the Earth's crust around two million years ago. It is the third largest and third deepest lake in Indonesia, plunging to a maximum depth of 450 meters. Located in the central highlands of Sulawesi, an island known for its unusual wildlife, the lake's long period of isolation has turned it into a site for evolution. This process, called adaptive radiation, has produced an explosion of species found nowhere else on the planet.
The lake itself covers an area of over 323 square kilometers and sits at an elevation of about 485 meters. Its waters are clear and drain from the town of Tentena at its northern end into the Poso River, which eventually flows to the Molucca Sea. This isolation and stability over a vast timescale provided the perfect conditions for aquatic animals to evolve into a variety of forms, filling every available ecological niche.
Radiations of Snails and Shrimps
The most spectacular examples of this evolutionary process are the lake's endemic snails and shrimps. The freshwater snail genus Tylomelania, often called "rabbit snails" by aquarists, has produced a large number of species unique to the lake. These snails have diverse shell shape and size, adapted to different substrates from soft sediment to hard rocks. At least four species of Tylomelania have been formally described from the lake, with many more awaiting scientific classification. The lake also has at least 14 species of the miniature snail genus Sulawesidrobia.
Equally impressive is the species flock of Caridina shrimps. There are 11 endemic species of these freshwater shrimps in Lake Poso. They have many different colors and have adapted to different lifestyles. Caridina caerulea can be found on the underside of rocks and logs, while Caridina ensifera forms swarms in open water. Another species, Caridina longidigita, uses its long appendages to filter food from the current.
Endemic Fish and Modern Threats
The lake's fish fauna is unique, with at least 11 endemic species. These include several types of ricefish from the genera Adrianichthys and Oryzias, such as Oryzias nigrimas, and gobies like Mugilogobius sarasinorum. A halfbeak, Nomorhamphus celebensis, is another fish found only in these waters.
Unfortunately, this unique biodiversity is under severe threat. The introduction of non-native fish species, including Mozambique tilapia, common carp, and flowerhorn cichlids, has led to a drastic decline in native fish populations. Some endemic fish may already be extinct. The surrounding ecosystem is also threatened by deforestation for mining and agriculture, and the construction of a hydroelectric dam on the Poso River has altered the lake's natural outflow.