Relic crabs

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Relic crabs
Mysis relicta..jpg

Relic shrimp ( Mysis relicta )

Systematics
Subclass : Eumalacostraca
Superordinate : Satchel Shrimp (Peracarida)
Order : Floating Shrimp (Mysida)
Family : Mysidae
Genre : Mysis
Type : Relic crabs
Scientific name
Mysis relicta
S. Lovén , 1862

The relict shrimp ( Mysis relicta ), also known as the split- foot shrimp , is a species of hover shrimp that lives in brackish or fresh water .

features

In the sexually mature state, in the fourth larval stage, relic crabs reach a length of about 1.5 centimeters, females can also reach a fifth stage with lengths of up to 22 millimeters. The animals have stalked compound eyes . The head and thorax are enclosed by the carapace except for the abdomen, where the legs used for swimming ( pereiopods ) attach . The abdomen has six segments, each of which carries a pair of pleopods . There is a pair of statocysts in the telson . The females have plates on the last two thorax segments under which they carry eggs and newly hatched young animals. In sexually mature males, the fourth pair of pleopods is elongated and probably serves to hold the female in place during mating.

distribution and habitat

Mysis relicta is only common in Northern Europe. The species is cold stenothermal and occurs mainly in waters with a high oxygen content. Accordingly, the species is more likely to be found in deep, oligotrophic to mesotrophic waters, rarely in eutrophic waters. The closely related species Mysis diluviana occurs in North America .

Way of life

Relict crayfish commute rhythmically between the water bed and higher water layers, staying mainly on the water bed during the day and migrating to higher water layers at night ( circadian rhythm ). The cause of the change in altitude is the light, because relic crabs are adapted to dark habitats. If the light intensity is too high, the eyes can be damaged.

Ecological importance

The relic crab is a typical example of glacial relic fauna : The species is widespread in regions of Eurasia that were covered with ice during the last glacial period . The southern limit of distribution of the species is where the glaciers ended in the cold period.

The relic crab and related species are prime examples of neozoa , which can have a serious impact on populated ecosystems . The North American species Mysis diluviana u. a. in the US in the state of Montana, where it significantly disrupts the established ecological interconnections in the Flathead Lake and Flathead River ecosystems. Mysis diluviana was released into the lake as an additional food source for the sockeye salmon ( Oncorhynchus nerka ) that were also released there. Instead of a source of food, the relic crabs became food competitors for salmon for the zooplankton . The salmon populations then collapsed. As a result, the populations of the bald eagles and grizzly bears , which the salmon serve as food, also decreased significantly.

Individual evidence

  1. ^ Mysis relicta in Zooplankton of the Great Lakes at Central University of Michigan
  2. ↑ a b Audzijonyte, A. & Väinölä, R .: Diversity and distributions of circumpolar fresh- and brackish-water Mysis (Crustacea: Mysida): descriptions of M. relicta Lovén, 1862, M. salemaai n.sp., M. segerstralei n.sp. and M. diluviana n.sp., based on molecular and morphological characters . In: Hydrobiologia . 544, No. 1, 2005, pp. 89-141. doi : 10.1007 / s10750-004-8337-7 .
  3. ↑ J. Horppila, A. Liljendahl-Nurminen, T. Malinen, M. Salonen, A. Tuomaala, L. Uusitalo, M. Vinni: Mysis relicta in an eutrophic lake: Consequences of obligatory habitat shifts. Limnol. Oceanogr., 48, pp. 1214-1222, 2003
  4. ↑ WATERSTRAAT, A., KRAPPE, M., RIEL, P. & RUMPF, M. (2005): Habitat shifts of Mysis relicta (Decapoda, Mysidacea) in the lakes Breiter and Schmaler Luzin (NE Germany). Crustaceana 78: 685-699.
  5. ↑ LINDSTRÖM, M. (2000): Eye function of Mysidacea (Crustacea) in the northern Baltic Sea. J. Exp. Mar. Biol. Ecol. 264: 85-101
  6. ↑ Väinölä, R. Riddoch, BJ, WARD, R. D, & JONES, RI (1994): Genetic zoogeography of the Mysis relicta species group in northern Europe and North America. Can. J. Fish. Aquat. Sci. 51: 1490-1505
  7. ↑ SCHRADER, G., UNGER, J.-G., GRÖGER, J., GORETZKI, J. (2002): Invasive alien species: A threat to biological diversity. Research Report - Journal of the Senate of the Federal Research Centers 2/2002: 12-16
  8. ^ Brendon Bosworth: How Non-Native Shrimp Transformed The Ecosystem at Montana's Flathead Lake NewWest January 21, 2011.

Web links

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