Uet era Ongael

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 Remengesau

Ongael Lake is the smallest and shallowest and youngest of the famous Palau jellyfish lakes. The area of the lake is 0.9 ha, maximum length roughly 100 meters and depth – up to 4 meters. Contrary to other jellyfish lakes Uet era Ongael is holomictic – wind and sea tides (through fissures in Miocene limestone) are well mixing the water and there is no accrued “dead” water at the bottom as it happens with deeper lakes.

Although lake is quite small it contains endemic subspecies of golden jellyfish Mastigias cf. papua remengesaui named after president of Palau Tommy E. Remengesau Jr. In the lake is met also another kind of jellyfish – Aurelia sp. and Cassiopea sp.

Mastigias of Ongael Lake is the most ornate of Palauan lake jellyfish – it is ornamented with solid white spots, smaller jellyfish is pale blue. This is a comparatively small jellyfish, diameter does not exceed 15 cm.

In Ongael Lake number of jellyfish fluctuates with an approximate one year cycle, sometimes it disappears, sometimes is abundant.

Lake is new (12 – 5 thousand years old) and it is truly amazing to see how quickly a new subspecies develops in such a small lake.

References

1. Coral Reef Research Foundation, Marine Lakes Research Accessed 08.02.10.
2. Jellyfish swarms, tourists, and the Christ-child. Mike N. Dawson, Laura E. Martin, Lolita K. Penland. Hydrobiologia 451: 131-144, 2001.
3. 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.