Anchialin is a technical term used in the ecology of water . It characterizes a special type of water that has an underground connection with the sea , but is clearly influenced by the inflow of fresh water from the land side, as seeping rainwater, groundwater or a cave water . It is primarily used for subterranean waters (cave waters), but can also refer to marine-influenced surface waters . Anchialine biotopes have a characteristic, independent fauna with numerous endemic species that can neither live in the sea nor in limnic waters. Relic forms live in anchialine caves in particular, which were also common in other waters in earlier geological ages, but could only survive here, and animals that otherwise have their distribution focus in the deep sea. Anchialine waters are characterized by brackish water , whereby there are often complicated conditions in which the (less dense and therefore lighter) fresh water overlays the salt water and a boundary layer, called halocline , is pronounced in between. Due to the connection to the sea, they are influenced by the tides .
Origin of the term
The term anchialin was first introduced in 1973 by the Dutch zoologist Lipke Bijdeley Holthuis . The expression is derived from the (Latinized) Greek anchialos which means "near the sea". Some ecologists later changed it to “anchihalin” (based on the Greek halos: salt), this variant is not wrong, but is used less often. Holthuis coined the term initially only for pool-like surface waters with (underground) connection to the sea (so-called "anchialine pools"), which occur in different places, but are particularly typical for the Hawaiian islands, where more than 100 of them used to occur .
Anchialine waters are characteristic of two different types of sea coasts: They occur on the one hand in karstified limestone , on the other hand in young volcanic rock with occurrences of lava caves . Karst cavities in the sea floor with sea water without land influence, known as " blue holes ", are normally not included. Many anchialine caves in karst rocks go back to earlier fluctuations in the sea level, through which karst caves could form in now flooded coastal areas, which means that there are often underwater stalactite formations. Almost all of them are either in tropical or at least in subtropical latitudes. Anchialine lava caves were found mainly on volcanic islands, in addition to Hawaii in the Canary Islands , the Galapagos Islands and (Western) Samoa . The Jameos del Agua lava tube on the island of Lanzarote is well-known and developed for tourists . The largest anchialine karst caves are located on the Mexican peninsula of Yucatán , their land-side openings are called cenotes . Others are located on the Caribbean islands, in the karst areas on the Mediterranean Sea and its islands, and they are also widespread in the Southeast Pacific, as far as Australia, but have so far been poorly researched here. Those of Ha Long Bay in Vietnam are known, for example . Anchialine karst caves are sometimes larger and often much older than volcanic lava tubes.
Hydrology and ecological conditions
On the seashore, underground fresh water and salt water usually do not meet on the coastline. The denser salt water often underlies the sweet groundwater in a wedge shape; on small islands this only forms a lens ( Ghyben-Herzberg lens ), which is underlaid by the seawater. But spring-like freshwater outflows in the sea can also occur with a high inflow of groundwater. A jump zone or halocline usually forms in the waters, in which the salinity changes more or less abruptly, which can range from a few centimeters to several meters in thickness. Because of the mixing, the overlying freshwater situation is mostly noticeably influenced by salt and more or less brackish . Even if, in temperate climates, the fresh water becomes denser in the cooler winter, it never reaches the density of lake water. There is therefore typically never complete mixing. This has u. a. As a result, the salt water in anchialine waters is shielded from the surface as if by a lid, and as a result it is often very poor in oxygen. Some anchialine crustaceans such as Halocaridina rubra can live in anoxic conditions without oxygen.
The primary production through photosynthesis fails in the lightless anchialine cave waters, these are therefore usually very poor in nutrients. Most of the nutrients are washed in as organic matter. In addition, especially in the halocline itself, there is chemoltotrophic production by sulfur-oxidizing bacteria , which oxidize the often abundant hydrogen sulfide in anoxic salt water to sulfur. As a result, the otherwise crystal clear water in this zone is clouded in some anchialine waters.
The anchialine fauna
The fauna of Anchialine waters is predominantly of marine origin. The group of crustaceans is particularly rich in species . The primeval Remipedia , which were only rediscovered in the 1980s, occur exclusively in anchialine cave waters; they are considered living fossils . The orders Mictacea ( satchel shrimp ) and Platycopioidea ( copepods ) do not occur anywhere else. The proportion of primitive Thermosbaenacea is also high . Although anchialine habitats form tiny islands on the edge of the world's oceans, some groups have a disjoint distribution over thousands of kilometers. Remipedia is available, for example, in the Caribbean, the Canaries and on the Western Australian coast. The decapode crab Procaris lives in Hawaii, the island of Ascension in the middle of the Atlantic, and the Bermuda Islands in the Caribbean. It is mostly assumed that this distribution pattern does not go back to long-distance spreading, but rather that it is a question of surviving relic forms, some of which trace the effects of continental drift. Some are considered to be Tethys relics. However, these hypotheses have so far hardly been tested using modern genetic methods.
Anchialine fish species are known in the families Bythitidae (eight species, from the Bahamas, Cuba, Yucatan, Galapagos), Eleotridae (one species, Australia), Gobiidae (three species, Philippines and Japan), Synbranchidae (two species, Yucatan and Australia) .
How many groundwater animals and cave animals are frequently white-colored, eyeless species. As with some deep-sea forms, crustaceans in anchialine waters are often colored bright red, especially in partial habitats under the influence of light.
Anchialine caves are usually difficult to access and must be explored by specialized cave divers , many of which are still little known to this day. As a special feature, rebreather diving devices are mostly used. The animals are usually recognized on the spot after their movement in the light cone of the lamps and captured in glass or plastic containers. The use of traps or nets is less widespread due to the technical difficulties and the often low density of individuals in the habitat.
- Jan H. Stock, Thomas M. Iliffe, Dennis Williams (1986): The concept “anchialine” reconsidered. Stygologia 2 (1/2): 90-92.
- Renée E. Bishop, William F. Humphreys, Neven Cukrov, Vesna Žic, Geoff A. Boxshall, Marijana Cukrov, Thomas M. Iliffe, Frano Kršinic, Willard S. Moore, John W. Pohlman, Boris Sket (2015): Anchialine redefined as a subterranean estuary in a crevicular or cavernous geological setting. Journal of Crustacean Biology 35 (4): 511-514. doi : 10.1163 / 1937240X-00002335
- LB Holthuis (1973): Caridean Shrimps found in Land-Locked Saltwater Pools at four Indo-West Pacific Localities (Sinai Peninsula, Funafuti Atoll, Maui and Hawaii Islands), with the description of one new genus and four new species. Zoological Negotiations Leiden 128 (1): 1-48. Download PDF
- Conservation Council for Hawai'i (editor): Anchialine Pools: Windows To Hawai'i's Underground Labyrinth. Poster Guide, 2011 PDF ( Memento of the original from November 29, 2016 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
- D. Jaume & GA Boxshall: Life in extreme ocean environments: anchialine caves. In: Carlos M.Duarte (editor): Marine Ecology. EOLSS Publications, 2009. ISBN 9781848260146
- Leontine E. Becking, Willem Renema, Nadiezhda K. Santodomingo, Bert W. Hoeksema, Yosephine Tuti, Nicole J. de Voogd (2011): Recently discovered landlocked basins in Indonesia reveal high habitat diversity in anchialine systems. Hydrobiologia 677: 89-105. doi : 10.1007 / s10750-011-0742-0
- Willard S. Moore (1999): The subterranean estuary: a reaction zone of ground water and sea water. Marine Chemistry 65: 111-125. doi : 10.1016 / S0304-4203 (99) 00014-6
- Justin C. Havird, Rebecca C. Vaught, Jeffrey R.Weeks, Yoshihisa Fujita, Michio Hidaka, Scott R. Santos, Raymond P. Henry (2014): Taking their breath away: Metabolic responses to low-oxygen levels in anchialine shrimps (Crustacea: Atyidae and Alpheidae). Comparative Biochemistry and Physiology, Part A 178: 109-120. doi : 10.1016 / j.cbpa.2014.08.015
- Boris Sket: Anchialine Caves. In: David C. Culver, William B. White (Eds.): Encyclopedia of Caves. Elsevier, Amsterdam et al. 2005, ISBN 0-12-198651-9 .
- Thomas M. Iliffe: Biodiversity in Anchialine Caves. In: David C. Culver, William B. White (Eds.): Encyclopedia of Caves. Elsevier, Amsterdam et al. 2005, ISBN 0-12-198651-9 .
- Jorge L. Pérez-Moreno1, Thomas M. Iliffe, Heather D. Bracken-Grissom (2016): Life in the Underworld: Anchialine cave biology in the era of speleogenomics. International Journal of Speleology 45 (2): 149-170. doi : 10.5038 / 1827-806X.45.2.1954
- Inken Krause: Dwarf shrimp in the saltwater aquarium. Natur und Tier Verlag, 2016. ISBN 9783866593640 .
- Thomas M. Iliffe & Louis S. Kornicker: Worldwide Diving Discoveries of Living Fossil Animals from the Depths of Anchialine and Marine Caves. In: Lang, Michael A., Macintyre, Ian G. and Rützler, Klaus: Proceedings of the Smithsonian Marine Science Symposium (Smithsonian Contributions to the Marine Sciences). Washington, DC: Smithsonian Institution Scholarly Press, 269-280.