Unio tumidiformis 

Scope: Global, Europe & Mediterranean
Language: English

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Taxonomy [top]

Kingdom Phylum Class Order Family
Animalia Mollusca Bivalvia Unionoida Unionidae

Scientific Name: Unio tumidiformis Castro, 1885
Taxonomic Notes: U. tumidiformis has been a neglected species in Spain and Portugal and replaces U. crassus in the southern Iberian Peninsula (Araujo in: Barea-Azcón 2008).

Assessment Information [top]

Red List Category & Criteria: Vulnerable A2ace ver 3.1
Year Published: 2011
Date Assessed: 2009-09-16
Assessor(s): Araujo, R.
Reviewer(s): Reischutz, P., Seddon, M. & Nichols, C.

This is one of the most imperilled Iberian naiad species (Araujo, pers. comm., 2009). The endemic nature, host specificity, restricted distribution, population status and threatened habitat of U. tumidiformis make this species of the main importance from a conservation point of view. In all its distribution area, the habitual droughts eliminate many specimens, putting the populations in permanent danger of extinction. The water extraction and pollution by the increase of industry and farm development in areas near the rivers where the species lives is a constant threat. A population is known in Spain which had thousands of specimens until 2005, but has been practically extinct after the drought. The population of the Ruidera lakes is endangered by water pollution, urbanism (hotels, recreation areas) and loss of host fish populations. Several sub-populations have disappeared in the last 50 years from the two of the five river basins (Guadiana and Guadalquivir). In the Guadalquivir basin, there is no record of living specimens today, so this sub-population is considered lost. Therefore this species is considered as Vulnerable A2ac based on estimated loss of 30–35% of populations using data from recent loss of parts of two out of five subpopulations, relatively restricted range (extent of occurrence under 20,000 km²), and the complete loss of all living specimens in one river basin as well as the decline in the sub-populations of the host-fish which are required for part of the life-cycle.

This species has also been assessed at the regional level:
EU27 regional assessment: Vulnerable A2ace at the level of the 27 member States of the European Union
European regional assessment:  Vulnerable A2ace
Mediterranean regional assessment:  Vulnerable A2ae

Geographic Range [top]

Range Description:

This species lives in the river basins of the south-western Iberian Peninsula. Live populations are distributed throughout the Guadiana, Mira and Sado river basins in Spain and Portugal. In Portugal it is known from Mira (Torgal River) and Sado basins. It occurs in several tributaries of the Guadiana river in Spain (Estena, Milagro, Bullaque, Guadalmez) and Portugal (Amoreiras, Azambuja, Barranco do Vidigao, Caia, Chança, Foupana, Limas, Lucefecit, Marmelar, Odeleite, S. Pedro, Terges e Cobres, Vascao). There is one population at the Ruidera lakes (Guadiana river, Spain). 

Countries occurrence:
Portugal (Portugal (mainland)); Spain (Spain (mainland))
Additional data:
Number of Locations:5
Range Map:Click here to open the map viewer and explore range.

Population [top]

Population:It is estimated that between 30 and 35% of the total populations have been lost in the last 50 years. The generation length is 15–25 years, providing three generations as 45–75 years. Also one subpopulation which had thousands of specimens until 2005 is now practically extinct after the drought in that year. There is one good population at the Ruidera lakes (Spain).
Current Population Trend:Decreasing
Additional data:
Continuing decline of mature individuals:Yes
Population severely fragmented:No
Continuing decline in subpopulations:Yes

Habitat and Ecology [top]

Habitat and Ecology:This species lives in temporary Mediterranean-type streams, on shores and slopes under the tree shadow, generally on sandy or muddy substrate at pool areas that do not dry up during the dry season. It can live in lakes (Ruidera lakes). In the dry seasons, specimens survive in isolated populations which take refuge in pools together with the fish.

Maturing of larvae (glochidia) is not always synchronous. Unio tumidiformis has proven to be an unusual host-specific species, apparently parasitizing only fishes of the genus Squalius, regardless of the mussel and fish species being sympatric or not. Successful encapsulation or complete metamorphosis was observed in five species: S. alburnoides complex, S. aradensis, S. caroliterti, S. pyrenaicus and S. torgalensis.
Generation Length (years):15-25

Use and Trade [top]

Use and Trade: This species is not used.

Threats [top]

Major Threat(s):

The habitat of this species is threatened by change of hydrologic regime of the streams, natural droughts, gravel extraction, water extraction, dams and impoundments. Loss of host fish, due to the introduction of exotic fish competitor, is also negatively affecting the species, as well as the increase of pollution due to intensive farming and industry.

Conservation Actions [top]

Conservation Actions: The species has been proposed for listing as Vulnerable A3c in the Spanish Red List of Invertebrates and as Vulnerable A2c; B1ab(iii)+2ab(iii) in the Andalusian Red List of Invertebrates. Special conservation interest must be devoted to the population of the Ruidera lakes. More research is needed on the population and distribution of this species, as well as on the habitat trends.

Citation: Araujo, R. 2011. Unio tumidiformis. The IUCN Red List of Threatened Species 2011: e.T171935A6810869. . Downloaded on 16 October 2018.
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