This species is known from Cameroon where it has been recorded from Mounts Manenguba, Nlonako, Kupe and Nta Ali, and at Fotabong in western Cameroon, and on the mountains around Yaoundé (Kala and Mbam-Minkoum) in southern Cameroon. There is also one specimen recorded from Equatorial Guinea on Monte Alén, although this may be another species and requires confirmation. Its altitudinal range is from 800-1,050m asl. It probably also occurs on the southern and western slopes of the Bamileke Plateau, and perhaps also on the Obudu Plateau in eastern Nigeria.
Habitat and Ecology
It is associated with rocks in streams and waterfalls in forest and degraded secondary habitats at the lower limit of the submontane zone, although it has also been found in leaf-litter away from water. On Mount Manenguba it occurs at a lower altitude than Werneria tandyi, although their ranges might overlap slightly. It breeds in streams.
It has been found to be reasonably common in suitable habitat within its small range.
This species is presumably affected by habitat loss due to agricultural encroachment and human settlement.
In Cameroon, the species occurs in a few forest reserves, such as Nta Ali Forest Reserve; however, the higher elevation forest habitats in western Cameroon, particularly Mount Manenguba, are in urgent need of improved protection. The specimen recorded from Equatorial Guinea was found in Monte Alén National Park in Equatorial Guinea, although confirmation of the taxonomic identity of this population is needed.
Jean-Louis Amiet 2004. Werneria mertensiana. In: IUCN 2014