Assessment Rationale:

Centromerus anoculus is only known from two lava tube systems on the island of Madeira, Portugal. This species is assessed as Critically Endangered (CR), since it has a very restricted geographic range (extent of occurence (EOO) and area of occupancy (AOO) are both only 8 km²) and there is a continuing decline in the EOO, AOO, quality of habitat and the number of mature individuals. Additionally, the number of locations is only two, based on the habitat degradation due to the use of caves by domestic animals, uncontrolled visits 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 threats.

Geographic Range:

Centromerus anoculus is only found in the lava tubes of Gruta dos Cardais in São Vicente, on northern Madeira Island, and Furnas do Cavalum in Machico, on eastern Madeira Island, Portugal (Wunderlich 1995, Reboleira et al. 2011). Gruta dos Cardais is part of the largest known cave system in Madeira. The neighbouring Grutas de São Vicente, which probably were once habitat for the species, are now in large part converted to show caves with extensive modifications in microclimate, including artificial lighting, water reservoirs and even newly built tunnels. Given the relative scarcity and small size of caves in Madeira, this could correspond to the entire range of the species although, as noted above, it probably is a junior synonym of C. sexoculatus. The extent of occurrence (EOO) and area of occupancy (AOO) are both 8 km².

Population:

The uncontrolled visits by tourists and locals that think of caves as adventure playground, accumulation of litter and use by domestic animals cause major changes in the cave environment and consequent decrease in quality of habitat for the species. This is believed to be leading to a decrease in population numbers, although no monitoring is being made and the rates are unknown.

 

Habitat and Ecology

This species is known from two lava tube systems. Ecology and traits are largely unknown as the only references to the species are from a short taxonomic description and a checklist. Yet, congeners are known to build sheet webs and this species might build them on cave walls on the hunt for insects.

Major Threat(s):

The species was probably driven away from part of its historical range by touristic activities that include digging of new tunnels, water regime modifications (artificial pools) and artificial lighting. Both current locations are threatened by use of caves by domestic animals, uncontrolled visits and accumulation of litter.

Conservation Actions

There are no specific conservation measures 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 two lava tube systems where it occurs with eventual restoration of natural conditions of the environment and recovery and re-introduction in the lost location. While this is not possible, or as an alternative, a strict code of conduct for touristic or other activities in caves should be enforced and both communication to the general public and training of touristic agents should be subject of a conservation plan. The taxonomical status of the species and possible synonymy with C. sexoculatus should be clarified. Research on both the species current population trend and the reasons for this 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.