The internationally protected Maltese Topshell, thought to have become extinct, rediscovered by researchers from the Department of Biology of the University of Malta
The Maltese Topshell, Gibbula nivosa, is a small, attractively coloured, marine snail that was first described by A. Adams in 1851. Since then, it has never been recorded from anywhere else in the Mediterranean apart from the Maltese Islands despite extensive searches by shell collectors. Such a situation is practically unique amongst marine molluscs within the whole Mediterranean region and the Maltese Topshell is firmly established as a Maltese endemic (that is, found only in the Maltese Islands and nowhere else in the world), and is protected by local (Flora, fauna and natural habitats protection regulations, 2006) and European Union legislation (the ‘Habitats Directive’) as well as by international conventions (the Bern Convention and the Barcelona Convention).
However, the Maltese Topshell seems to be rare even within the Maltese Islands themselves. In 1978, an Italian worker searched thirteen different sites round the Maltese Islands for this species but found live individuals only in St. Thomas Bay. After this, there were no records of live individuals for over 25 years in spite of intensive searches carried out at sites where it used to occur. The Maltese Topshell has therefore been considered critically endangered and some malacologists have speculated that it may be extinct.
In 2006, researchers from the Department of Biology of the University of Malta discovered a population of Gibbula nivosa on the northeastern coast of Malta, and in 2008, a second population off western Comino, showing that the Maltese Topshell is not extinct. These discoveries provided the researchers – postgraduate student Julian Evans (funded through a Malta Government Scholarship Scheme grant), and Dr Joseph A. Borg and Prof Patrick J. Schembri – with the opportunity to study the basic biology of the Maltese Topshell for the first time and to provide data on the ecology and behaviour of this snail. Such information is essential for the conservation management of the species.
These studies indicated that the snails are active at night but hide during the day, a behaviour that is probably a defence against day-hunting predators. They feed indiscriminately on organic material that they browse off the substratum. Young snails entered the population at the end of summer, suggesting that Gibbula nivosa spawns in early summer. The snails seem to attain adult size in less than a year. Large seasonal fluctuations in abundance were observed, implying that population size is very variable and may be quite low at certain times of the year.
Given these new data, the conservation status of G. nivosa was re-evaluated. Since this species is only known from a single location (the Maltese Islands) and the entire population is fragmented (so far, only two populations are known, one in Malta and one in Comino), and because there has been a decline in its extent of occurrence as the populations in places where it was previously common (e.g. St. Thomas Bay) seem to have disappeared, the Maltese Topshell is still be considered as critically endangered.
This work has been published in the prestigious international scientific journal Marine Biology.
Picture: Two live individuals of the endemic Maltese Topshell, Gibbula nivosa (© 2010 Julian Evans)
"Species is protected in Malta and the European Union and that it is illegal to collect or to possess specimens without a permit"
Department of Biology of the University of Malta