Potamon tauricum Czerniavsky, 1884
Synonyms: Potamon antiquum Szombathy, 1916
Common names: Engl: Freshwater crab; Rom: Crab de apa dulce; Russ: Presnovodny krab; Turk: Tatli su yengeci; Ukr: Prisnovodny krab
Taxonomic descriptions: The carapax length is up to 4 cm in adult individuals, width - up to 5 cm. The total animal weight is about 50 g. Its ambulatory leg digits are lengthened. The shell is olive-brown on its upper part, and from light-brown to red underneath; nippers are tinged with purple.
World level: DD
Black Sea Regional level: DD
Subregion level: EN in Ukraine
Habitats type, Critical habitats, Limiting factors. The crab is an inhabitant of mountain rivers and streams, but it is absent in their upper waters and estuaries. Upstream distribution is limited because of the low temperature of the water, downstream it is obstructed by water salinity and pollution. Crabs survive during temporary drying up events: they hide in deep burrows and cavities under the stones, and use torrents under river-beds. Crabs occur in artificial ponds, however they do not breed in stagnant water. They usually visit land at night time and during the rains, and can subsist without any water for a long time in a humid air environment. In the Black Sea region P. tauricum is known in Crimean, Caucasian, Anatolian and Bulgarian coastal areas.
Biology. The animal is euryphagous: detritus, green filamentous algae, fallen leaves, olygochaetes, amphipods, insect larvae, molluscs, frogs (including tadpoles), fishes and carrion are suitable food. Crabs eat any feed of plant or animal origin in captivity. Cannibalism is usual. Copulation and spawning take place during a year, predominantly in the warm season from June till October. Fertility is very low in comparison with sea crabs: each female contains not more than 200 eggs. Completely formed young animals appear in 1-2 days from the roe that had been put on female pleopods. For the first 5-7 days youngs are localized under a female pleon, where they feed and grow up to 3.6 mm; then they gradually adopt to an independent life mode.
Population trends. Since the mid 1970s there is a distinct tendency of a decline in population abundance and distribution area in Ukraine (south coast of the Crimea); some biotops have already disappeared, the others are endangered.
Threats. Direct habitat destruction by river-bed straightening and water reservoirs building, mass surface flow withdrawal for local water-supply systems, and also water pollution by non-purified sewage are the main anthropogenous causes of population degradation. Sometimes crabs can be caught for food or for aquariumists.
Conservation measures taken. The species is listed in the Red Data Book of Ukraine.
Conservation measures proposed: Complete inventory of locations; the monitoring of populations; special reservations creation.
Compiled by: S. Krivokhizhin