Marine lake
Marine lakes (engl. Marine lakes ) are bodies consisting of sea water , which are completely surrounded by land. They have a superficially invisible connection to the sea, which enables an exchange of the water and keeps the salt content in the lake essentially constant and as high as in sea water. Lake level and sea level are essentially the same. Marine lakes are by definition not salt lakes , a term for inland waters with salt water without runoff or connection to the sea. However, transitions or intermediate stages are possible. Marine lakes represent habitat islands with biogeographical, ecological and evolutionary features that are reminiscent of "real" islands. A total of around 200 marine lakes are currently known worldwide. The most famous marine lake is Ongeim'l Tketau , also known as Jellyfish Lake, on the island of Eil Malk in the South Pacific island state of Palau .
Location and age of today's marine lakes
Around 200 marine lakes are currently known around the world. Their number is likely to increase, however, as they are often referred to as such in the literature only by chance. They are essentially concentrated in four regions in the world: the Bahamas , Vietnam , Palau and Papua New Guinea . These regions are characterized by karstified coasts that have been flooded by the rise in sea level after the last glacial period . Most of the marine lakes were formed as depressions in a karstified landscape, which were flooded with sea water through tunnels and crevices as a result of the rise in sea level after the last glacial maximum (approx. 18,000 years ago). The physical characteristics of today's marine lakes have only formed over 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 lying directly on the karst were directly dated to 10,000 years using radiocarbon analyzes. In the case of shallow lakes or depressions, the age, i.e. the time of the flooding, can be estimated based on the sea level rise known over time. Marine lakes are not limited to these four main regions, but occur worldwide, for example in Croatia ( Dragon's Eye Lake ), Greece and even in Antarctica .
Physical characteristics
Today's marine lakes have sizes from about 50 m to about 2000 m and depths of around 1.5 m to about 60 m. They are often only a few meters away from the sea, but can also be many hundreds of meters away from the sea. They are surrounded by ridges that are usually only a few tens of meters high, and rarely several hundred meters high. All marine lakes have a measurable tidal cycle , which can, however, differ more or less from the tidal cycle in the surrounding sea. The marine lakes near the coast are often connected to the sea by tunnels through which divers can swim. With lakes a little further away, the connections to the sea are often not so clearly visible. The water exchange takes place through many smaller gaps. Depending on this connection to the sea and the associated water exchange, the physical properties of the lakes vary. They range from holomictic lakes, which have the same temperature as the near sea, are well ventilated to the bottom and have a salinity of 34 PSU , to meromictic lakes, which are caused by subdued tidal influx, high precipitation, strong sunlight, sheltered locations and that Absence of distinct seasons, are vertically stratified by temperature and salinity and / or are anoxic in depth, or are temporary or permanent, more or less brackish. Marine lakes form a continuum from lagoon-like to water bodies that are strongly isolated from the sea. Marine lakes thus represent a wide spectrum of habitats and corresponding fauna communities, which also have the potential for species to change or new species to emerge in a short time.
Biological quirks
The Ongeim'l Tketau on Palau is known for the abundance of a jellyfish of the genus Mastigias ( Mastgias cf. papua ). Millions of specimens live almost constantly in this lake and migrate daily in the morning from the western part to the eastern part and back to the western part in the afternoon. Detailed morphological and molecular genetic studies have shown that the population is already so different from the parent species (which still lives in the lagoons off Palau today) that it can be interpreted as a separate subspecies. This also applies to the jellyfish populations of four other marine lakes on Palau; each of these lakes is home to its own subspecies of Mastigias cf. papua . Due to the depth of the lake and the thickness of its sediments (around 60 m), the evolution of this subspecies can only have taken place in the last 10,000 years. In the shallower other marine lakes on Palau with the four other subspecies Mastigias cf. papua there was even less time available for the evolution of the subspecies, as these are even shallower and the depressions contain less sediments. So far, however, there have only been preliminary studies on the biological inventory of marine lakes. It is estimated that 10 to 20% of the species and subspecies of marine lakes have not yet been scientifically described.
swell
Individual evidence
- ↑ Maša Surić, Mladen Juračić, Nada Horvatinčić, Ines Krajcar Bronić: Late Pleistocene – Holocene sea-level rise and the pattern of coastal karst inundation: records from submerged speleothems along the Eastern Adriatic Coast (Croatia). In: Marine Geology. 214, 2005, pp. 163-175, doi : 10.1016 / j.margeo.2004.10.030 .
- ↑ Stelios Katsanevakis: Population dynamics of the endangered fan mussel Pinna nobilis in a marine lake: a metapopulation matrix modeling approach. In: Marine Biology. 156 (8), 2009, pp. 1715-1732, doi : 10.1007 / s00227-009-1206-1 .
- ↑ John P. Bowman, Suzanne M. Rea, Sharee A. McCammon, Tom A. McMeekin: Diversity and community structure within anoxic sediment from marine salinity meromictic lakes and a coastal meromictic marine basin, Vestfold Hills, Eastern Antarctica. In: Environmental Microbiology. 2 (2), pp. 227-237, doi : 10.1046 / j.1462-2920.2000.00097.x .
- ↑ Michael N. Dawson: Five new subspecies of Mastigias (Scyphozoa: Rhizostomeae: Mastigiidae) from marine lakes, Palau, Micronesia. In: Journal of the Marine Biological Association of the United Kingdom. 85, Plymouth 2005, pp. 679-694, PDF
literature
- Michael N. Dawson, Laura E. Martin, Lori J. Bell, Sharon Patris: Marine Lakes. In: Rosemary Gillespie, Davis A. Clague (Eds.): Encyclopedia of Islands. University of California Press, Berkeley / Los Angeles / London 2009, ISBN 978-0-520-25649-1 , pp. 603-607.