This species is endemic to Tanzania. It is known only from the Mrora Forest on Mafia Island, from the Jozani Forest on Unguja Island (Zanzibar), and from an unmapped, unspecified locality in the east of Unguja. All records are from close to sea level and its extent of occurrence (EOO) is 912 km2.
Habitat and Ecology
It is terrestrial, occurring in lowland coastal forest. Some of its remaining habitat is degraded, and it seems to display some adaptability to living in such habitats. Its breeding behaviour is unknown, but it might breed in puddles in tree roots like Mertensophryne anotis.
It is probably an uncommon species and its population is suspected to be decreasing due to ongoing decline in the quality and extent of its habitat.
The quality and extent of its habitat on Mafia is declining rapidly due to agricultural activities, wood extraction, and expanding human settlements.
There is ongoing encroachment of thickets and forest of Unguja - including Jozani Forest - for small-scale agriculture and other human uses. In addition, because the island is formed of coral rag - a highly permeable substrate - a serious water issue is unfolding within its range as ever-increasing misuse of freshwater by the growing human population and unplanned development (including tourism) (T. Davenport pers. comm. October 2015).
No protection is given on Mafia Island though it is possible the species occurs in the terrestrial part of the Mafia Marine Park, but this remains to be confirmed. On Unguja, it occurs in Jozani-Chwaka Bay National Park which has the largest tract of forest remaining on the main island; it also occurs in Kiwenga Forest Reserve.
Improved protection of remaining suitable habitat on Mafia is a priority and with the Jozani-Chwaka Bay National Park.National Park.
Further information is required on the species' distribution, breeding strategy, and population status.
Red List Status
Listed as Endangered because its extent of occurrence (EOO) is 912 km2, it occurs in two threat-defined locations, and there is continuing decline in the extent and quality of its habitat on Unguja and Mafia Islands.
IUCN SSC Amphibian Specialist Group 2016. Mertensophryne howelli. The IUCN Red List of Threatened Species 2016: e.T54888A84397243. http://dx.doi.org/10.2305/IUCN.UK.2016-1.RLTS.T54888A84397243.en