|Scientific Name:||Potamon fluviatile (Herbst, 1785)|
Potamon fluviatilie Capolongo & Cilia, 1990 ssp. lanfrancoi
Potamon fluviatilis (Herbst, 1785) [orth. error] ssp. fluviatilis
Potamophilus edule Latreille, 1818
|Taxonomic Notes:||Subfamily Potaminae. Pretzmann (1983) recognised five subpopulations for this species (as Potamon (Telphusa) fluviatilis fluviatilis, which he called nations), mainly for populations that inhabit islands in the Aegean and Mediterranean. The subspecies Potamon fluviatile lanfrancoi Capolongo and Cilia, 1990 was also not recognised by Brandis et al. (2000). This species was revised to Potamon (Eutelphusa) fluviatile by Brandis et al. (2000) and is treated here as Potamon fluviatile.|
|Red List Category & Criteria:||Near Threatened ver 3.1|
|Reviewer(s):||Cumberlidge, N. & McIvor, A.|
Despite the wide distribution of this species (E00 800,000 km²) and the relatively high number of localities and records, some of its populations (especially those on islands) are discontinuous and highly fragmented, and the threat level is high, so there is cause for concern for the future of some of its isolated subpopulations. Although the wide distribution and high number of records for this species might imply that it should be assessed as Least Concern, the balance of evidence indicates that populations of this species may nevertheless be under immediate and long-term threat from rapid anthropogenic changes affecting its habitat such as water diversion, drainage, habitat disturbance, over-harvesting, and pollution. This species is therefore assessed here as Near Threatened (NT) because it is possible that populations of P. fluviatile in parts of its range might be in danger of extirpation in the future, especially those on islands or near centres of human population on the mainland. It is considered to be close to qualifying for category A2 (possibly also A3 and A4) under population reduction, and may already be sufficient to qualify as VU but data are lacking.
|Range Description:||Potamon fluviatile has a highly fragmented geographic distribution over a wide area in a number of countries that have a Mediterranean coastline. This species is found in Italy (Trento, Lombardia, Veneto, Liguria, Toscana, Umbria, Lazio, Campania, Puglia, Calabria, Sicily Provinces), the Maltese Islands (Malta and Gozo), the Balkan Peninsula (Croatia, Montenegro, Macedonia, Albania), and Greece (western mainland Greece plus the Ionian islands and western Aegean islands). In mainland Greece the Axios River in the Macedonian Province marks the easternmost point of its distribution. It is found in the Axios,Kalamas, Aheron, and Arachthos River drainages, and in Peloponnesos in the Pinios, Piros-Tethreas, Pamisos, and Evrota River drainages. The distribution of P. fluviatile also includes the provinces of Pella, Trikala, Larisa, Fthiotis, Prevenza, Aitolia-Akarnania in western Greece, and the Peloponnesian provinces of Korinthia, Arkadia, and Lakonia. Potamon fluviatile is also found on the Ionian islands (Kerkyra (=Corfu), Kefallinia, Lefkas, Zaknythos (=Zante)); on the Northern Sporades Islands: Skiathos and Skopelos islands (Magnesia Province), Evvoia island and Skyros island (Evvoia Province), and in the Cyclades island of Andros.|
Native:Albania; Croatia; Greece (Greece (mainland)); Italy (Italy (mainland), Sicilia); Macedonia, the former Yugoslav Republic of; Malta; Montenegro
|Range Map:||Click here to open the map viewer and explore range.|
|Population:||Population levels of Potamon fluviatile have declined dramatically in recent years throughout its range. This trend towards a decline in population levels is often explained as the result of factors such as pollution, overharvesting, and habitat damage (Matthews and Reynolds 1995, Gherardi and Holdich 1999). More recently, the introduction of non-indigenous crayfish species into southern European waters may pose a further threat to freshwater crab survival (Gherardi and Holdich 1999). In the Maltese islands P. fluviatile has disappeared from a number of valleys either because its habitat has dried up, or because the springs that feed the water body have been polluted, or because it has been over-harvested by humans for food. In Greece, crabs used to be common in the Gallicos River system on the plain west of Thessaloniki, but none were found in surveys in the 1990s. This loss is attributed to the introduction of intensive agriculture here in the 1970s-1980s and to the increased use of insecticides, pesticides, and water draw-off for irrigation (Pretzmann 1993). Similarly, in 1978 the only living population of crabs on the island of Andros (Cyclades) was found near Meldano, and crabs were not found during searches elsewhere on the island where these animals.|
|Current Population Trend:||Decreasing|
|Habitat and Ecology:||This species is found in rivers, streams and lakes throughout its range. In the Northern Apennine mountains in Tuscany, Central Italy, P. fluviatile lives in streams that are part of the Arno and Reno river basins (ranging from 155 to 596 m a.s.l.) that flow through wooded areas over both calcareous and siliceous rocks (Nocita et al. 2006, Barbaresi et al. 2007). In streams and rivers crabs shelter under stones or among vegetation, or they rest in their burrows dug into the banks; burrows are up to 50 cm deep and have water at the bottom. Crabs are most active between May and October, after which (i.e., from November to February) they are less active and hibernate either in natural refuges or inside burrows (Gherardi et al. 1988, Gherardi et al. 1998). Crabs feed at night either in water or on land, and they are opportunists that consume a wide variety of food items, that is either dead or alive, plant of animal. Food items include vegetable matter, tadpoles, insects, small frogs, and fish. Crabs have few predators, but they are vulnerable to habitat degradation, over-harvesting, and pollution (despite the population of crabs in an unpolluted part of the city of Rome). Young crabs are more aquatic than adults, and females mate in late spring and release hatchlings in summer. Crabs are semi-terrestrial and spend time out of water either at night or in the day when it is raining. Crabs are capable of dispersal by walking on land across relatively short distances to reach nearby streams.|
Many freshwater habitats in the Mediterranean region where P. fluviatile occurs (Italy, Greece and the Maltese Islands) are increasingly subjected to unprecedented levels of human disturbance, and the future rate of species extirpation in these habitats is predicted to be almost five times greater than that for terrestrial animals and three times that of coastal marine mammals (Ricciardi and Rasmussen 1999). For example, since 1900 Greece has lost an estimated 75% of its wetlands due mainly to human activities. Many populations of river crabs are now in urgent need protection, especially those populations that are found on the Mediterranean islands. Potamon fluviatile is associated with streams and rivers and it is important that these habitats be protected from pollution and drying out. Growth of agro-business (for fruits and agrarian products) and of tourism (hotels) have caused local water pollution and have placed large demands on the supply of fresh water. Also, increasing use of pesticides and insecticides on fields has caused increasing contamination of ground water, ponds, and streams. In some places stream beds have been concreted to make water channels and this has adversely affected crab populations by preventing them from digging burrows for shelter and breeding. An increasing volume of water is being extracted from streams and rivers in pipelines to supply hotels, factories, villages, industry and agriculture, and this is causing drying and a subsequent loss of aquatic habitat.
Interestingly, studies on P. fluviatile in Italy indicate that the main factors affecting its distribution are anthropogenic pressures and uncontrolled harvesting rather than specific alterations to the biotic and abiotic parameters of its aquatic habitat.
Studies in mainland Greece indicate that P. fluviatile may be threatened by pollution and habitat alterations. Populations of this species in the Axios River delta (along with the Aliakmon delta and Loudias and Gallikos rivers) live in a protected area that consists of wetlands of great ecological and international importance (Ramsar convention). However, even this habitat is now threatened by industrial pollution (from the disposal of industrial solids and liquid wastes from tanneries, slaughterhouses, pig farms, and phosphoric fertilizer factories), by sewage sludge, and by water extraction for irrigation and electric power production. Additional threats to crab habitat come from pesticides and herbicides, uncontrolled river sand extraction, alluvial deposits, overgrazing, overfishing, poaching, and arbitrary building.
Current national and international conservation efforts aimed at preventing populations of freshwater crabs in the Mediterranean region from decline are generally inadequate due to a general lack of knowledge of crab ecology and biology, and to long-term neglect (until recently) driven by the low economic value of these animals. The distribution of P. fluviatile in the Southern Tuscan Apennines (and presumably in the rest of its range) is not obviously associated with any biotic or abiotic parameters (Vannini and Gherardi 1981, Barbaresi et al. 2007). For example, this species is not highly sensitive to environmental conditions and occurs in waters that have relatively high minimum and maximum temperatures, variable oxygen levels, a wide range of dissolved ions, and different bedrock types. In addition, high concentrations of calcium in their water does seem to affect crabs, presumably because calcium is an essential element for crustacean exoskeletons. Informal field observations of river crabs in urban areas indicate that P. fluviatile may be quite resistant to some kinds of water pollution.
Leaf litter is a common component of the diet of crabs but it is not the sole source of protein for these animals (Gherardi et al. 1987). Shelters and burrows in streams are vital for survival because adult crabs seek refuge either in burrows or under riparian vegetation and juvenile crabs hide under pebbles and cobbles to avoid predation by fishes and adult conspecifics. The conservation of these freshwater crabs depends heavily on habitat protection and the preservation of freshwater ecosystems. Given the crisis that populations of native freshwater decapods are facing (Gherardi and Holdich 1999, Füreder et al. 2002) it is imperative that conservation planners make the most effective use of information currently available. The protection of river crabs needs to be strongly regulated at all levels of legislation (from community to regional levels) in order to guarantee the preservation of crabs throughout their distributional range. In Italy, Potamon fluviatile is protected by local regulations and regional laws but these have been adopted by only a few regions (Latium, Tuscany, Liguria, and Abruzzo), and are often not sufficient to preserve this species from decline. For example, crabs are not found in every part of suitable habitats within their range. The presence of crabs in some streams and their absence in similar streams nearby may be the result of over-exploitation by fishermen who continue to poach crabs despite the protection of crabs by local laws, an explanation that is supported by reports from local people and by long-term researchers. Today the pressure on freshwater resources ranges from moderate to intense, and some species have either been reduced or even locally extirpated from parts of their range. There is at present very little effective management and conservation in many parts of the distributional range of this species. Existing plans for managing aquatic inland resources primarily focus on water use and do not include specific, enforceable monitoring and management objectives, conservation actions, and little being done to
protect either aquatic habitats and communities or endangered and threatened species.
Recommendations. Rivers and streams should be protected against drying. Perennial rivers, and those rivers that normally flow for only part of the year, should be protected against extended seasonal drought because these are vital habitats for aquatic freshwater animals. Stream and river beds should not be concreted to make channels and water pollution should be prevented. Water pollution should be prevented, and the collection of crabs for food should either be banned or regulated.
|Citation:||Cumberlidge, N. 2008. Potamon fluviatile. The IUCN Red List of Threatened Species 2008: e.T134293A3933275.Downloaded on 14 December 2017.|
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