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Deckenia mitis

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Taxonomy [top]

Kingdom Phylum Class Order Family
ANIMALIA ARTHROPODA MALACOSTRACA DECAPODA POTAMONAUTIDAE

Scientific Name: Deckenia mitis
Species Authority: Hilgendorf, 1898
Taxonomic Notes: This genus was formerly assigned to the family Deckeniidae Ortmann, 1897. The genus Deckenia is now assigned to the Potamonautidae: Deckeniinae: Deckenini: Deckenina (Cumberlidge et al. 2007). This species was described by Ng et al. (1995) and Reed and Cumberlidge (2006), and its distribution was updated by Marijnissen et al. (2005).

Assessment Information [top]

Red List Category & Criteria: Near Threatened ver 3.1
Year Published: 2008
Date Assessed: 2008-01-01
Assessor/s: Cumberlidge, N.
Reviewer/s: Cumberlidge, N. & Marijnissen, S. and McIvor, A.
Justification:
Listed as Near Threatened (close to VU under A2c), because although its extent of occurrence is more than 20,000 km² and it is known from a large number of localities in three different countries, there is evidence that there is an on-going and major decline in the extent and quality of its habitat (marshes, wetlands) which is fragmented and declining, and there are long-term threats to its habitat from disturbance and pollution.
History:
2004 Vulnerable

Geographic Range [top]

Range Description: Tanzania and Kenya. The type locality is Wembere Steppe near Tabora (5°02’S, 32°50’E) in Tanzania, and Ng et al. (1995) reported on material from Kilimantinde (5°52’S, 34°55’E), Dar es Salaam, and at a non-specific locality in southern Tanzania near Lake Malawi (as Nyassa Lake). The combination of all known localities for D. mitis (Marijnissen et al. 2005) indicates that this species is found in both inland and coastal localities in Tanzania (Dodoma, Tanga, Iringa, Mount Meru, Amani, South Pare Mountains, Kibno, Kilimantinde and Dar es Salaam) and in Kenya (Murangía, Taveta and
Mombasa).

Kenya: Deckenia mitis is found in two inland localities in Kenya (Murang’a and Comarock on the Athi plains), as well as several localities on the coastal lowlands (Marijnissen et al. 2005).

Tanzania: D. mitis is found on the coastal lowlands and inland near Mount Meru, near Lake Victoria, and on the Wembere Steppe north of Tabora. There is also a literature report of D. mitis from a locality in southern Tanzania close to lake Malawi but this has not been confirmed (see Marijnissen et al. 2005). Surveys in the Usambara-Tanga region suggest that D. mitis is restricted to the lower edges of the montane forest and to coastal plains, where it inhabits burrows near the edge of slow-moving streams or near stagnant water bodies such as ponds and wells (Williams et al. 1964). In Tanzania, 17 specimens of D. mitis were collected from their burrows in a wetland area (0,5 km²) near Segera (5°18’S, 38°39’E), and an additional 13 specimens were collected from burrows beside ponds near Mwang’ombe (5°04’S, 39°06’E).
Countries:
Native:
Kenya; Tanzania, United Republic of
Range Map: Click here to open the map viewer and explore range.

Population [top]

Population: Recent field studies in Tanzania indicate that the quantity and quality of freshwater habitats available to this species have decreased drastically over the past several decades and that habitat disturbance could be a major factor in driving declining population levels of this species. While It is difficult to estimate the population status and trends of this species, it is likely that its population is declining based on indirect factors such as the lack of recent specimens from many parts of its range, its poor representation in museum collections and increasing habitat disturbance from loss of wetlands associated with growing human populations in the region (IUCN 2004).
Population Trend: Decreasing

Habitat and Ecology [top]

Habitat and Ecology: This species exhibits a preference for areas with stagnant surface water in habitats that include wetlands, streams, and slow-flowing rivers. This species inhabits burrows dug into soft, silt-clay types of sediment and appear to avoid course-grained, sandy soils. The burrows of D. mitis reach down to the water table. This is also observed in other African burrow-dwelling freshwater crab species including Sudanonautes monodi (Cumberlidge 1987), P. obesus (S.A.E. Marijnissen, pers. obs.), and Afrithelphusa monodi (Cumberlidge 2006a,b), where such burrows ensure crabs a constant water supply during dry periods. It is thus likely that the area of occupancy of D. mitis within its distributional range is limited by its restriction to areas with a high groundwater level. Deckenia mitis prefers marshes and low lying wetlands, and is an air-breathing amphibious species. Williams et al. (1964) provided some observations on the habitat of D. mitis caught in an arid area of northern Tanzania close to Mount Meru. Specimens of D. mitis were collected in warm stagnant surface waters, and never in the cooler streams flowing down mountain slopes. Deckenia mitis and P. obesus share the same habitat and burrow deeply into the soil at the waters edge, often causing extensive damage to drainage ditches.
Systems: Freshwater

Threats [top]

Major Threat(s): Between 1970 and 1990 the human population in East Africa has more than doubled and it is still growing rapidly (UNEP 2004). The effects of increasing human population growth on the loss of freshwater habitats through deforestation and agricultural encroachment are recognized as the major threats to freshwater biodiversity in the East African region (Darwall et al. 2005). Recent field studies in Tanzania indicate that the quantity and quality of freshwater habitats available to this species have decreased drastically over the past several decades and that habitat disturbance could be a major factor in driving declining population levels of this species. There are immediate threats from increasing habitat disturbance from loss of wetlands associated with growing human populations in the region (IUCN 2004). Marijinissen et al. (2005) argued for the upgrading of the conservation status of D. mitis to Vulnerable based on new field studies and new population estimates.

Conservation Actions [top]

Conservation Actions: No conservation measures are known to be in place for this species and it is not found in a protected area.
Citation: Cumberlidge, N. 2008. Deckenia mitis. In: IUCN 2013. IUCN Red List of Threatened Species. Version 2013.2. <www.iucnredlist.org>. Downloaded on 19 April 2014.
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