Conservation of the critically endangered, micro-endemic, Maltese top-shell

Abstract

Species with very narrow native distributions, or micro-endemics, are of special conservation interest. While not uncommon in terrestrial environments, micro-endemism is much less well known in the marine realm. With a geographic range spanning a few kilometers, the Maltese Top-shell Steromphala nivosa (formerly Gibbula nivosa), a small gastropod that is endemic to the Maltese Islands (central Mediterranean), is a rare example of extreme micro-endemism in the marine environment. Its narrow range and fragmented population make it a critically endangered species whose continued survival depends on adequate conservation measures. Knowledge of the biology of a species is a prerequisite for proper conservation management but it was only after 2006, when a live population of S. nivosa was rediscovered after a 25-year gap since the previous known sighting, that studies on its ecology and behavior were first undertaken. Applying knowledge of its current distribution, abundance, population dynamics, habitats, ecological interactions and behavior, the main threats and pressures faced by this species were identified as those relating to habitat alteration or destruction. These include pollution (chemical pollution or nocturnal illumination) and activities such as coastal development that cause physical disturbance of the seabed where its habitat occurs. Conservation actions to control development and pollution that may affect the species’ habitat are therefore required. The best way to implement such actions is by designating marine protected areas, but the main sub-population of the Maltese Top-shell is located within a harbor with intense marine activity and ongoing coastal development. This particular and peculiar situation, where a very rare and highly endangered micro-endemic species was discovered in an area that has long been a harbor, presents conservation managers with a singular problem of how to balance conservation and socio-economic considerations.