Cymbula nigra is the largest limpet in the Mediterranean. It has been listed since 1993, as an 'endangered species'. Its historical range in the Mediterranean includes the southern Spanish, the Moroccan and the Algerian coasts. Recent observations have confirmed its proliferation in southern Spain and its progression along the European and North African Mediterranean coasts. Field surveys carried out along the Tunisian coasts during winter 2011 revealed the presence of this species in the Gulf of Tunis and the Cap Bon. The finding of C. nigra represents a range extension possibly enhanced by the current global warming, as it is a 'warm-water species'. The absence of records in previous surveys to the same sampling sites (2006)(2007), together with the small sizes recorded in 2011, confirms the recent installation of the species. The limpet was recorded in areas spared of pollution, characterized by a predominant influence of the Atlantic current, and also showed a preference for steep cliffs exposed to strong waves. This is the first population study of this endangered gastropod outside of its original range of distribution. The determination of the ecological characteristics of newly colonized habitats might serve as a starting point for the establishment of appropriate recommendations for its conservation. R esum eCymbula nigra est la plus grande patelle de la M editerran ee. Elle est class ee depuis 1993 comme «esp ece en danger». Son aire de r epartition historique dans la M editerran ee inclut les côtes sud de l'Espagne ainsi que les côtes marocaines et alg eriennes. De r ecentes observations confirment sa prolif eration dans le sud de l'Espagne et sa progression le long des côtes m editerran eennes europ eennes et nord-africaines. Des etudes de terrain r ealis ees le long des côtes tunisiennes pendant l'hiver 2011 ont r ev el e la pr esence de cette esp ece dans le Golfe de Tunis et au Cap Bon. La d ecouverte de C. nigra repr esente certainement une extension de l'aire de r epartition favoris ee par le r echauffement climatique actuel puisqu'il s'agit d'une «esp ece d'eau chaude». L'absence de traces lors de pr ec edentes prospections des mêmes sites de pr el evements (2006)(2007), ainsi que les petites tailles enregistr ees en 2011, confirment l'installation r ecente de cette esp ece. L'esp ece a et e rapport ee dans des zones epargn ees par la pollution et caract eris ees par une influence pr edominante du courant Atlantique, et elle montre egalement une pr ef erence pour des falaises abruptes expos ees a de fortes vagues. Ceci est la premi ere etude de la population de ce gast eropode en danger r ealis ee en dehors de son aire d'origine. La d etermination des caract eristiques ecologiques d'habitats des habitats r ecemment colonis es pourrait servir de point de d epart pour l' etablissement de recommandations appropri ees pour sa conservation.
Imposex has been observed in several regions of the world to affect many species of prosobranch gastropods such as Stramonita haemastoma (Linnaeus, 1767). This irreversible sexual anomaly is caused mainly by the accumulation of organotin compounds in tissues. The present study aimed to confirm the existence of imposex and to determine the different levels of infection in individuals of Stramonita haemastoma collected from different stations along the rocky coastline of the Gulf of Tunis. To do this, 10 stations covering the entire rocky coastline of the gulf were sampled during March-May 2012. Rates of occurrence of imposex suggest that sexual modifications occur to different degrees in this species in all sampled stations of the gulf. The most contaminated sites were harbour areas (Sidi Bou Said and La Goulette). In addition, an inverse relationship between the distances from potential sources of pollution and the occurrence of this sexual anomaly was observed. It should be noted that toxic effects induced by marine xenobiotics could cause the loss of biodiversity and the disruption of this ecosystem stability.
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