Marine lake
Marine lakes (English marine lakes ) are water bodies consisting of sea water, which are completely surrounded by land. They have a superficial non-visible connection to the sea, which allows replacement of the water and keeps the salt content in the lake is substantially constant and as high as in sea water. Lake level and sea level are substantially the same. Marine lakes are thus, by definition, no salt lakes, a designation for inland waters, salt water with no outlet or connection to the sea. But transitions or intermediate stages are possible. Marine lakes provide habitat islands is with biogeographic, ecological and evolutionary features that are reminiscent of "real" islands. Total known world currently has about 200 marine lakes. The most famous marine lake is the Ongeim'l Tketau, even Jellyfish Lake Jellyfish Lake, or called, on the island of Eil Malk in the South Pacific island nation of Palau.
Location and age of today's marine lakes
Currently one knows about 200 marine lakes worldwide. However, their number is likely to increase, as they are often just also happens to be referred to in the literature so. They are essentially concentrated in four regions in the world: the Bahamas, Vietnam, Palau and Papua New Guinea. These regions are characterized by karst coasts, which have been flooded by rising sea levels after the last ice age. Most marine lakes originated as a depression in a karst landscape that have been (approx. 18,000 years ago) flooded as a result of sea level rise after the last glacial maximum through tunnels and columns with seawater. The physical properties of today's marine lakes have all formed only during the last 20,000 years, the shallower lakes often only in the last 10,000 years ( or even later ). In a lake in Palau, the sediments overlying the karst were directly, directly dated with radiocarbon analyzes on 10,000 years. In shallower lakes or depressions can be the age, ie the time of the flooding, estimated on the basis of sea level rise over time known. Marine lakes but are not limited to these four main regions, but occur world-wide, such as in Croatia ( Dragon's Eye ), Greece and even in Antarctica.
Physical properties
Today's marine lakes have sizes of about 50 m to about 2000 m and a depth of about 1.5 m to about 60 m. They are often only a few meters from the sea, but can also be separated hundreds of meters from the sea. You are surrounded by land back, only a few tens of meters are high usually are rare even several hundred meters high. All marine lakes have a measurable tidal cycle, but may differ from the tidal cycle in the surrounding sea, more or less. The marine lakes near the coast are often connected by tunnels to the sea, you can swim through the divers. For more distant lakes connections to the sea are often not as clearly seen. The water exchange occurs over many smaller columns. In response to this connection to the sea and the associated exchange of water vary the physical properties of the lakes. They range from holomikten lakes that have the same temperature as the nearby sea, are well ventilated to the bottom and have a salinity of 34 PSU, up to meromictic lakes, which by muted Tidenzufluss, high rainfall, intense sunlight, sheltered position and the absence of pronounced seasons, are layered vertically by temperature and salinity, and / or in the depths are anoxic, or are temporarily or permanently more or less brackish. Marine lakes form a quasi- continuum of lagoon -like to highly isolated from sea water bodies. Marine lakes thus represent a wide range of habitats and corresponding faunal, which also have the potential to change styles in a short time and new species can arise.
Biological peculiarities
The Ongeim'l Tketau on Palau is known for the mass occurrence of jellyfish of the genus Mastigias ( Mastgias cf papua ). Million copies almost constantly live in this lake and hike daily in the morning from the western part to the eastern part and the western part of the afternoon back to back. Detailed morphological and molecular genetic studies have shown that the population is already so different to the original species ( which still lives in the lagoon in front of Palau ) that they can be interpreted as a distinct subspecies. This also applies to the jellyfish populations four other marine lakes on Palau; each of these lakes includes its own subspecies of Mastigias cf papua. Due to the depth of the lake and its sediments thickness (about 60 m) may have occurred, the evolution of this subspecies only in the last 10,000 years. In the flatter other marine lakes of Palau with the other four subspecies Mastigias cf papua stood for the evolution of subspecies even less time available, as these are even flatter and the depression contain less sediment. So far there is only preliminary studies on the biological inventory of marine lakes. It is estimated that 10 to 20% of species and sub- species of marine lakes are not well understood.