KOROR STATE GOVERNMENT MARINE TOUR GUIDE ... - C3

3.7 Marine Lakes & Jellyfish
Marine Lakes: Tour Guide Training Manual
By Laura E. Martin, Michael N Dawson, Lori J. Bell
Coral Reef Research Foundation
What is a marine lake?
The limestone ‘Rock Islands’ of Koror and Airai States are dotted with a little known but
unique type of marine ecosystem called a marine lake. Simply defined a marine lake is a
body of seawater surrounded by land. Although generally unrecognized as such, marine
lakes, like coral reefs and mangrove forests, are a widespread type of marine
ecosystem.
Marine lakes form where seawater flows through channel, tunnel and fissure ridden
landmasses to fill depressions in the landscape that are lower than sea level. Imagine a
colander sitting in a sink partly filled with water. The colander is the tunnel-riddled island,
its center the lake, and the water outside the colander the ocean. Marine lakes cannot
form where there are no depressions lower than sea level and the land is relatively
impermeable to the ocean. This is why Babeldaob lacks them.
All marine lakes retain connections to the ocean via tunnels or channels through the
encircling rock and thus, experience tides. The number, size and length of the channels
through which water must flow determine the degree to which water and organisms are
exchanged with the ocean. Broad, short tunnels facilitate high exchange and are
characteristic of marine lakes with coral reef like communities. Longer, less direct
connections isolate the lake and its organisms from the sea. These lakes typically
support mangrove communities and organisms able to tolerate lower salinity waters that
result from dilution by rain.
In 1999, Koror State legally defined a marine lake as “any body of water that is
separated from the ocean by rocks, island, land barrier or which is cut off from the ocean
at low tide even if there is a tunnel or cave which links another part of the marine lake to
the ocean waters” (KSPL NO. K6-95-99). Under this definition, Koror State recognizes
about 50 marine lakes in its waters. Another commonly offered number is about 70. In
practice, the tally will depend upon the specific definition used.
How did the marine lakes form?
All of Palau’s marine lakes can be thought of as young lakes in comparatively old rock
islands. Palau’s remarkable rock islands formed many millions of years ago as tectonic
forces slowly pushed coral reef out of the ocean, creating land with the topographical
characteristics of reefs: a complex network of high ridges and steep faces interspersed
with depressions, all formed of limestone perforated by channels and fissures.
The marine lakes are the product of the porous nature of the islands in relation to height
of the surrounding ocean (sea level) which, over the last 20,000 years, has changed
profoundly in response to changes in the earth’s climate. During the earth’s most recent
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