Testing ground for evolution
Each of the marine lakes of Palau has a specific set of species occasionally trapped in lakes by the receding sea 15 – 10 thousand years ago. Some lakes have steeper banks, some are elongated in an east-west direction, some in a south-north direction. Every such detail leads to different circumstances and consequently – different new species and subspecies of animals.
Some marine lakes of Palau are made even more exotic by the fact that they are meromictic – below the upper layer of marine water there is a layer of "dead", anoxic water separated by a layer of floating microorganisms, including a purple bacteria.
Such unusual monuments of nature serve as excellent “testing ground” for studies of evolution. Thus lately several scientists have made interesting treatises about these lakes. Lucky them (scientists!) – making science in beautiful Palau…
Jellyfish of president Salii
Clear Lake is small (just 3.9 ha) and its maximum length is just some 330 meters, the age of the lake – approximately 12,000 years. Depth reaches 30 meters, purple-sulfur bacteria layer is located in the depth of 15 – 16 meters, below there is an anoxic layer of water without life.
Although the lake is small, here lives endemic subspecies of jellyfish – Mastigias cf. papua salii, named after the third president of Palau Lazarus Salii.
Species composition in Clear Lake is similar to species composition in Jellyfish Lake. Here also lives a predator of jellyfish – sea anemone Entamaea medusivora.
But there is an important difference – while the Jellyfish Lake is elongated in the east-west direction, Clear Lake is stretched in the north-south direction. It seems that this seemingly slight difference has a big influence on the fauna of the lake. The border between the seawater and anoxic water in Clear Lake is more diffuse and oxygen level is falling already at 6 – 10 meters depth.
This is the most likely reason why jellyfish in Clear Lake appears sporadically, while in Jellyfish Lake there always (almost) is a lot of jellyfish.
Jellyfish of Clear Lake also has daily migration pattern, although less pronounced than in Jellyfish Lake, here jellyfish does not evade from shadow.
In order to survive sea anemone also had to elaborate different behavior – besides the jellyfish it consumes mussels as well.
- Coral Reef Research Foundation, Marine Lakes Research Accessed 08.02.10.
- Jellyfish swarms, tourists, and the Christ-child, Mike N. Dawson, Laura E. Martin, Lolita K. Penland. Hydrobiologia 451: 131-144, 2001.
- Five new subspecies of Mastigias (Scyphozoa: Rhizostomeae: Mastiigidae) from marine lakes, Palau, Micronesia, Michael N. Dawson. Journal of Marine Biological Association, U.K. 2005., 85., 679-694. Accessed 08.02.10.
Clear Lake on the map
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|Location, GPS coordinates:||7.15270 N 134.35923 E|
|Categories:||Animal colonies, Ecosystems, Lakes and streams|
|Where is located?||Australia and Oceania, Micronesia, Palau, Koror, Rock Islands, Eil Malk (or Mecherchar)|
|Alternate name:||Clearwater Lake|
|Dominating species:||Mastigias cf. papua salii|
“name”: “Clear Lake”,
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