Assessment Rationale:

G. coronula is listed as Critically Endangered, based on a very restricted range and area of occurrence, limited to a single known site on Deserta Grande, which lies on a slope landslide area. Although Deserta Grande is within a protected area, the present declining quality of the habitat due to grazing by goats and the possibility of habitat degradation in the future with reducing rainfall and the increased duration of droughts may have a dramatic impact on the habitat. Moreover, the restricted number of mature individuals in the single known population, which are threatened by predators such as mice and the endemic carabid beetles, along with the genetic isolation of the known population, dictate that the species is assessed as Critically Endangered (CR B1ab (iii,v)+2ab(iii,v); D). 

Geographic Range:

This species is endemic to the Madeira Archipelago (Portugal), where it was originally described by Lowe (1852) from a Quaternary fossil deposit from the southern parts of Bugio Island (Wollaston 1878, Cameron and Cook 1999). It was later found by Paiva (1867) living on Deserta Grande, where it was considered rare. After more than 140 years without any records, Teixeira and Silva found a single extant population in 2013, in a northern slope of Deserta Grande Island (Teixeira et al. 2017

Population:

There is no information on population trends, although the species is extremely rare and very localised, being presently restricted to a single extant population (Teixeira et al. 2017). The population is thought to be declining, primarily as a result of ongoing habitat degradation and predation.

Habitat and Ecology

According to Paiva (1867), the species was found living under rocks covered by lichens. It was found recently living on a slope area originated by a landslide, under boulders and large rocks covered by lichens and amongst grasses (Teixeira et al. 2017)

Major Threat(s):

The major threat for this species is habitat degradation/loss through grazing by domestic goats (Capra hircus) and erosion in the form of landslides. The active predation by mice (Mus musculus) and the potential predation by endemic carabid species (Scarites abbreviatus desertarum and Eurygnathus latrellei wollastoni) is a recognized threat to the current population (Teixeira et al. 2017). Moreover, the genetic and reproductive isolation of the species, confined to a single population, may compromise the species' perenniality over time. In addition, the predicted climate change effects in the form of drought, is also a threat to be dealt with.

Conservation Actions

This species occurs in a protected area of the Desertas islands, which is both a Nature Reserve and a Special Area for Conservation (SAC) under the Natura 2000. The species will indirectly benefit from the habitat restoration action and the goat control program in place on Deserta Grande island under the LIFE Recover Natura (2013-2019). In addition, a mice eradication program is critically needed, once this species is the major predator for the G. coronula. Further work is urgently needed on habitat and population monitoring for this species, as the area where the species is now found is extremely vulnerable to landslides and there is no information about population trends.