Sea frog

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Sea frog
Sea frog (Pelophylax ridibundus) from Krk / Croatia

Sea frog ( Pelophylax ridibundus ) from Krk / Croatia

Systematics
without rank: Amphibians (Lissamphibia)
Order : Frog (anura)
Subordination : Neobatrachia
Family : Real frogs (Ranidae)
Genre : Water frogs ( pelophylax )
Type : Sea frog
Scientific name
Pelophylax ridibundus
( Pallas , 1771)
Croaking sea frogs

The sea ​​frog ( Pelophylax ridibundus , Syn . : Rana ridibunda ) belongs to the family of real frogs (Ranidae) within the order of the frog auger. In addition, it is reckoned according to appearance, way of life and relationships to the water frogs , which are now placed in their own genus Pelophylax . The sea frog is considered a “good species”, but its exact distribution has not yet been conclusively clarified. Terra typica of the species is Atyrau (formerly Gurjev) in Kazakhstan , at the northern end of the Caspian Sea. Very little is known about the biology of sea frogs in this region in particular; an analysis of the calls is available.

features

Sound image (oscillogram) of four pulse groups from a mating call by a male sea frog. Tape recording on May 20, 1990 near Atyrau, Kazakhstan. The water temperature was 20 ° C
Younger female sea frog from East Friesland with back line and grass-green (pond frog-like) coloring and drawing
The back stripe can also be missing on some specimens; In this animal from Hesse, the large spots and the gray basic color are also noticeable

The head-torso length ranges from 10 to 16 centimeters; Specimens over 10 centimeters are mostly females. The upper side is mostly olive-green or olive-brown, in Central Europe hardly any grass-green, with distinct dark spots. The green dorsal center line typical of the water frog is usually present. The inner thighs are marbled white-gray and black (yellow parts are usually missing); the paired vaults of the males are dark gray. The body is similar to that of its relatives, the small water frog and the pond frog , but with different proportions. The hind legs or lower legs are very long in relation to the trunk. The heel hump is small and flat.

Calls and call behavior

The males call "oäk, oäk" (district call) as well as loud and sonorous "reck-keck-keck-keck-keck" (mating call) in a choppy sequence of sounds so that it sounds like a vigorous laugh (compare type epithet ridibundus = the laughing one ). Paragraphs of the calls are common, but they do not convey any precise information about the characteristics of the calls.

The mating calls of the sea frogs from Atyrau, Kazakhstan, consist of an average of 8.16 pulse groups at a water temperature of 20 degrees Celsius, these have an average duration of 50.2 milliseconds, the intervals between them measure 44 milliseconds, the average number of pulses per pulse group is 18. The dominant frequency range extends from 1400 to 2400 Hertz.

During the investigations at Atyrau from May 11th to May 21st 1990, calls between 13.2 degrees Celsius and 25.6 degrees Celsius were registered. All important call characteristics are correlated with the water temperature. As the water temperature rises, the duration of the impulse groups, the intervals in between, as well as the duration of the pairing calls and the pauses between them decrease, the number of impulses per impulse group remains unaffected. All changes are clearly noticeable when hearing the calls.

In addition to the pairing call, there are three types of territorial calls that differ audibly due to the composition of the pitches and the structure of impulses. Revierruf Type 1 is the call that is described as "Oak" and from which the term "croak" is derived as a kind of onomatopoeia. The acoustic characteristics of the district calls are also correlated with the water temperature.

Reproduction

In Central Europe, mating usually takes place between the end of April and the end of May. The females deposit several spawning balls with a total of up to 16,000 eggs one after the other in water . A single ball of spawn contains several hundred eggs. The spawn balls sink and remain submerged. The diameter of the eggs is 1.5 to two millimeters, they are brownish on top, the lower pole is light yellow in color.

Older tadpoles , with a greenish basic color and a dark pattern of spots, are noticeable for their impetuous escape reactions . The total length ranges from 40 to 80 millimeters. A differentiation from other water frog tadpoles is not possible with certainty.

Habitat and Distribution

Natural lake in the Elbe valley lowlands

The sea frog has a very close connection to water. Even young animals are only a few meters away from the water. Seefrösche prefer it bigger, eutrophic water bodies in the area of flood plains, such as lakes, backwaters, oxbow lakes , flood channels, quiet stretches of river, Bracks, larger ponds and lakes, sometimes channels and wide trenches. A rich water and bank vegetation is an advantage, but there should be no shading by trees. There the animals like to sit on the shoreline and sunbathe. In the event of danger or disturbance, they immediately jump into the water. In contrast to most other frogs, overwintering takes place mainly in aquatic sediments . The species is therefore dependent on oxygen-rich, rarely completely or long-term freezing water.

Until recently, the sea frog was assigned a large distribution area. After that it occurs in Central and Eastern Europe as well as in the Middle East and Central Asia and in the Balkans. In Germany, the area dissolves from east to west into discontinuous sub-areas that conspicuously coincide with the large river landscapes. In the north-west German lowlands, pure populations of the sea frog in East Friesland and the Wesermarsch are remarkable. A large distribution gap in Mecklenburg-Western Pomerania of all places ( Mecklenburg Lake District !) Is noticeable.

According to this information, the area of ​​the sea frog includes areas with both a continental climate, e.g. B. in the terra typica in Kazakhstan, as well as with Mediterranean and desert climate. This requires a great deal of adaptability of this kind.

food

Sea frogs feed on insects , spiders , worms and also cannibally on smaller frogs and conspecifics as well as their larvae. The tadpoles eat (filter) diatoms , green algae , rotifers , animal protozoa , detritus and the like; later they also scrape off soft water plant particles. In older specimens, however, the proportion of animal food also increases (such as small crabs, annelids). Spawning cannibalism also occurs.

Hazard and protection

Front view

Because of their relatively stationary way of life, sea frogs are probably less threatened than many other amphibian species. Even in some fish ponds - which should at least have reed-covered banks - they can survive better than the other amphibians (with the exception of the common toad ). However, at the edge of its range, including in Germany, the species often does not seem to have as great ecological potential as at the center of its range. This is reflected in the strong concentration on river valleys and marshes, while large regions in between are unpopulated.

Legal protection status (selection)

National Red List classifications (selection)

  • Red List Federal Republic of Germany: not endangered
  • Red list of Austria: VU (corresponds to: endangered)
  • Red list of Switzerland: NE (not rated)

literature

  • Bettina Diekamp, ​​Hans Schneider: Neuronal processing of conspecific and related calls in the torus semicircularis of Rana r. ridibunda Pall. (Anura): single-unit recordings. Journal of Comparative Physiology, Volume A 163, 1988, pp. 301-315.
  • Rainer Günther: Europe's water frogs. - Neue Brehm-Bücherei 600, Wittenberg (Lutherstadt) 1990, ISBN 3-7403-0234-8 .
  • Rainer Günther (Ed.): The amphibians and reptiles of Germany. G. Fischer-Verlag, Jena 1996, ISBN 3-437-35016-1 .
  • Birgitt Kuhn, Hans Schneider: Mating and territorial calls of the frog Rana ridibunda and their temperature-dependent variability. In: Zoologischer Anzeiger. Volume 212, 1984, pp. 273-305.
  • Susanne Lenné, Hans Schneider: The sea frog in Northern Hesse: evidence, calls, call behavior. In: Hessian Faunistic Letters. Volume 14, 1995, pp. 51-62.
  • Robert Mertens, Heinz Wermuth: The amphibians and reptiles of Europe. Waldemar Kramer Verlag, Frankfurt am Main 1960, 264 pp.
  • Eviatar Nevo, Hans Schneider: Structure and variation of Rana ridibunda mating call in Israel (Amphibia: Anura). In: Israel Journal of Zoology. Volume 32, 1983, pp. 45-60.
  • Andreas Nöllert, Christel Nöllert: The amphibians of Europe. Franckh-Kosmos, Stuttgart 1992, ISBN 3-440-06340-2 .
  • Hans-Joachim Obert: The dependence of calling activity in Rana esculenta Linné 1758 and Rana ridibunda Pallas 1771 upon exogenous factors (Ranidae, Anura). In: Oecologia (Berl.). Volume 18, 1975, pp. 317-328.
  • Jörg Plötner: The western Palearctic water frogs - from martyrs of science to a biological sensation. In: Supplement to the magazine f. Field Herpetology Volume 9, Bielefeld 2005, ISBN 3-933066-26-3 .
  • Hans Schneider, Theodora S. Sofianidou: The mating call of Rana ridibunda (Amphibia, Anura) in northern Greece as compared with those of Yugoslavian and Israeli populations: proposal of a new subspecies. Zoologischer Anzeiger, Volume 214, 1985, pp. 309-319.
  • Hans Schneider: Bioacoustics of the Froschlurche - native and related species. With audio CD. In: Supplement of the journal for field herpetology. Volume 6. Laurenti Verlag, Bielefeld 2005, ISBN 3-933066-23-9 (audio samples: 12.1–12.3.).
  • Hans Schneider, Josef Brzoska: The liberation calls of the Central European water frogs. In: Zoologischer Anzeiger. Volume 206, Jena 1981, pp. 189-202.
  • Ulrich Sinsch, Barbara Eblenkamp: Allozyme variation among Rana balcanica, R. levantina, and R. ridibunda (Amphibia: Anura). Genetic differentiation corroborates the bioacoustically detected species status. Journal for Zoological Systematics and Evolutionary Research. Volume 32, 1994, pp. 35-43.
  • Theodora S. Sofianidou, Hans Schneider, Ulrich Sinsch: Comparative electrophoretic investigation on Rana balcanica and Rana ridibunda from northern Greece. Alytes, Vol. 12, 1994, pp. 93-108.

Web links

Commons : Sea Frog ( Pelophylax ridibundus )  - Collection of images, videos and audio files

Individual evidence

  1. ↑ Robert Mertens, Heinz Wermuth: The amphibians and reptiles of Europe. Waldemar Kramer Verlag, Frankfurt am Main 1960, 264 pp.
  2. ^ A b c d Hans Schneider, Eduard Murasovitch Egiasarjan: The structure of the calls of Lake Frogs (Rana ridibunda: Amphibia) in the terra typica restricta. In: Zoologischer Anzeiger. Volume 227, 1991, pp. 121-135.
  3. ↑ Hans Schneider: Bioacoustics of the Froschlurche - native and related species. With audio CD. In: Supplement of the journal for field herpetology. Volume 6. Laurenti Verlag, Bielefeld 2005, ISBN 3-933066-23-9 .
  4. ^ Andreas Nöllert, Christel Nöllert: The amphibians of Europe. Franckh-Kosmos, Stuttgart 1992, ISBN 3-440-06340-2 .
  5. ↑ Seefrosch at www.wisia.de
  6. ↑ Federal Agency for Nature Conservation (ed.): Red list of endangered animals, plants and fungi in Germany 1: Vertebrates. Landwirtschaftsverlag, Münster 2009, ISBN 978-3784350332 .
  7. ↑ Online overview at www.amphibienschutz.de .