Malta’s endangered snail finds place in global encyclopedia

The Maltese Top-shell Steromphala nivosa – a miniscule, 3-9 mm long, attractively coloured marine snail that is endemic to Malta, has found a place in a compendium of Earth’s endangered species and ecosystems.

The Maltese top shell, which occurs in Maltese waters and nowhere else in the world, was thought extinct until rediscovered in the Sliema Creek in Marsamxett harbour in 2006. In 2010 a number of live individuals were also found in Comino.

An entry written by three leading Maltese biologists recently featured in in ‘Imperilled: The Encyclopedia of Conservation’, which documents the threats to earth’s imperiled species and ecosystems in one big comprehensive encyclopedia.

Previous studies dating back to 1978 had documented the presence of the species at St Thomas Bay in Marsaskala, here the species was first documented in 1851. But studies in 2000 yielded no live individuals.

The species is recognised as a critically endangered one and is protected by EU directives and its extinction in Malta would also mean its global extinction.

An entry to the encyclopedia by leading Maltese biologists Dr. Julian Evans, Prof. Joseph A. Borg and Prof. Patrick J. Schembri, dwells on the challenge posed by the “peculiar situation” where a very rare and highly endangered species was discovered in an area that has long been a harbour. This presents conservation managers with a singular problem of how to balance conservation and socio-economic considerations.

But the narrow range and fragmented population of the species make it a critically endangered species whose continued survival depends on adequate conservation measures.

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 behaviour were first undertaken.

These studies showed that the main threats and pressures faced by this species are habitat alteration or destruction. These include chemical pollution, nocturnal illumination and activities such as coastal development that cause physical disturbance of the sea bed. “Conservation actions to control development and pollution that may affect the species’ habitat are therefore required,” the biologists said.

The species is typically found in shallow waters up to 5m in depth. Earlier scientific research had identified the seagrass Posidonia oceanica as its main habitat. However, recent discoveries have indicated that cobble beds are also an important habitat for this species. The Maltese Top-shell is a nocturnal species, known to venture at night to forage for food and then return under stones during the day to evade predation.