MAIISG

Assessment Rationale:

Centromerus sexoculatus is only known from a single lava tube system on the island of Madeira, Portugal. This species is assessed as Critically Endangered (CR), since it has a very restricted geographic range (extent of occurrence (EOO) and area of occupancy (AOO) are both only 4 km²) and there is a continuing decline in the EOO, AOO and the number of mature individuals. Additionally, the number of locations is only one, based on the habitat degradation due to uncontrolled visits to the caves and accumulation of litter. The remaining habitat of the species needs to be protected and a management plan for the habitat as well as the species should be implemented. More research is needed, especially into the taxonomy, the population trend and the ecology of the species.

Geographic Range:

Centromerus sexoculatus is only found in the lava tubes of Furnas do Cavalum, close to Machico on eastern Madeira Island (Wunderlich 1992), although, if the synonymy with the more widespread C. anoculus is confirmed, it occupies two cave systems (see assessment for the latter species). Given the relative scarcity and small size of caves in Madeira, this could correspond to the entire range of the species. The extent of occurrence (EOO) and area of occupancy (AOO) are both only 4 km².

Population:

A single subpopulation exists of unknown size. The population is assumed to be decreasing, inferred by the threats of visits to the caves and accumulation of litter (Reboleira et al. 2011) which decrease the habitat quality and ability of the species to occupy its full historical range.

 

Habitat and Ecology

Centromerus sexoculatus is known from a single lava tube system, Furnas do Cavalum, Machico. This is a troglobiont species with considerable eye reduction, depigmentation and appendage elongation. Ecology and traits are largely unknown as the only reference to the species is from a short taxonomic description. However, congeners are known to build sheet webs and this species might build them on cave walls on the hunt for insects.

Major Threat(s):

This species is possibly threatened by uncontrolled visits to the caves and accumulation of litter (Reboleira et al. 2011) which decrease the habitat quality and ability of the species to occupy its full historical range. Based on this threat it only occurs in one location.

Conservation Actions

No specific conservation measures are in place for this species. Furnas do Cavalum are considered scientific patrimony by the "Plano Director Municipal" of Machico. Yet, this cave species would benefit from effective protection with adequate legislation of the lava tube system where it occurs with eventual restoration of natural conditions of the environment and recovery of its population. It should also be formally protected by adequate legislation. The taxonomical status of the species and possible synonymy with C. anoculus should be clarified. Research on population trends and its causes is needed to know the real threat levels and how to minimize them. A species conservation plan and a management plan would improve its survival chances for the future.