IUCN SSC Mid-Atlantic Island Invertebrates Specialist Group

Species

BackGeomitra grabhami (Wollaston, 1878)

Geomitra grabhami (Wollaston, 1878)

  • Kingdom: Animalia
  • Phylum:
  • Class: Mollusca
  • Order: Gastropoda
  • Family: Hygromiidae
CR Critically Endangered
IUCN Red List Status:

Countries of Occurrence:
Portugal - Madeira

Archipelago(s):
Madeira

Reviewer/s:
: Neubert, E. & Allen, D.J.

Contributor/s:

Facilitators / Compilers/s:


Assessment Rationale:

This species is endemic to Deserta Grande Island in the Madeira Archipelago. The species was known from the northern end of the island, where it was recorded as recent shells by Groh and Hemmen (1986), but it was not refound by Cameron and Cook (1999). However the species was recently found living at a new locality, Fajã Grande, on the eastern coast of the island by Teixeira and Silva in 2008 and again by Teixeira and Isamberto when resurveyed in 2013. The species is found on a coastal plateau formed by the collapse of coastal cliffs, where there is a threat of further landslide and erosion. There is also a threat from predation from mice, which have not been eradicated yet, and there is an increase in the frequency of droughts, which impacts both the species as well as adding to ground instability. The species is assessed Critically Endangered (CR B1ab(iii)+2ab(iii)) based on a single location with an assumed small population with ongoing threats. There is a Life Project survey work ongoing to monitor the status of this species and a species conservation action plan is planned for 2019. The species should be reassessed if future fieldwork refinds the species at the original locality at the northern end of the island, or finds further new localities.

Geographic Range:

This species is endemic to the Madeira Archipelago, where it is known from subfossil records in the Castanheira Valley at the northern end of Deserta Grande (Groh and Hemmen 1986). The species was not refound by Cameron and Cook (1999), however, live specimens were found in 2008 by Teixeira and Silva at Fajã Grande on the eastern coast of Deserta Grande and again in 2013 (Teixeira and Isamberto; D. Teixeira pers. comm. 2016).

Regions:
Portugal - Madeira
Extent of Occurrence (EOO):
(km2)
Area of Occupancy (AOO):
(km2)
Elevation Lower Limit:
(m)
Elevation Upper Limit:
(m)
Biogeographic Realms:
Palearctic
Presence:
Extant
Origin:
Endemic Madeira
Seasonality:
Resident

Population:

The species was originally considered extinct by Waldén (1983), although recent shells were found in the Castanheira Valley in 1986 (Groh and Hemmen 1986). The species was found at the new locality at Fajã Grande on the eastern coast of Deserta Grande by Teixeira in 2008 and again in 2013 (D. Teixeira pers. comm. 2016). There are no data on population size or trend, however, there are likely to be a very small number of specimens (less than 500 mature individuals).

Habitat and Ecology

This species was originally described as living among lichens growing on rocks (Seddon 2008). At the currently known location at Fajã Grande, the species is found amongst large boulders on a plateau area formed by a large landslide and erosion below steep cliffs, c.15 m asl (D. Teixeira pers. comm. 2016).

Major Threat(s):

Currently, overgrazing by introduced goats has been reduced, but it originally caused ground instability and erosion which covers the entire island. The species is currently known from a recently-formed coastal plateau area below steep cliffs, where there is a threat of ground instability and land-slips. There is also a threat from predation by mice, which have not been eradicated yet. There is an increase in the frequency of droughts, which impacts both the species as well as adding to ground instability. The workstation of the Parque Natural da Madeira (the body that supervises the nature reserve) is at Fajã Grande.

Conservation Actions

This species has long been considered Extinct by Waldén (1983) and Regnier et al (2008). There had been survey work in the period between 1970 and 2000 that had failed to locate populations, but in view of the nature of the terrain it was considered plausible that a small population may survive in areas that are less accessible, hence was placed as Critically Endangered (Possibly Extinct) by Seddon (2008, 2011). Work on the rehabilitation of the vegetation following the removal of the goat populations started. Further work on rehabilitation of the plant communities on the islands are ongoing, and this may benefit the land-snail populations. There is survey work ongoing through a Life Project to monitor the status of this species and a species conservation action plan is planned for 2019. The entire island of Deserta Grande is a candidate AZE for this and other species.