The impact of alien vascular plants in the aquatic habitats of a mediterranean island: preliminary data and observations in Sicily

Abstract

As is well known, invasive alien species pose a major global threat to the conservation of biodiversity, causing the extinction of native species and modifying ecosystem functions: this is true also for aquatic habitats, particularly susceptible to invasion due to usually high disturbance regimes and easy dispersal of propagules. The island of Sicily is one of the main hotspots of plant biodiversity, in the center of the Mediterranean basin; it hosts different types of freshwater habitats, both lentic (coastal wetlands, saltworks, temporary ponds, lakes, reservoirs) and lotic (springs, streams, permanent and seasonal rivers). As a first step of our analysis of the effects of the alien vascular plant species on the aquatic habitats of the island, an updated list of these alien species reported for the Sicilian aquatic habitats has been compiled, including archeophytes (to be considered a minor threat because of the long amount of time since their introduction) and neophytes; we used the term “aquatic plants” in its broadest sense to include all plants that occur in permanently or seasonally wet environments, distinguishing emergent, submergent and floating species. As regards floating species, in the last years new alien species, such as Lemna minor L., and new populations of already reported alien species, such as Eichhornia crassipes (Mart.) Solms, have been reported. A similar trend has been verified also for the emergent species (e.g. the new alien species Typha laxmannii Lepech.). From available data it is clear that additional research on the field is needed. We focused our attention on wetlands in protected areas; in fact they usually are delicate areas hosting rare species and/or ecosystems. The study of functional traits (such as gas exchange, leaf area index, leaf nutrient and chlorophyll concentrations, etc.) of invasive alien species can aid in predicting their impact on the evolution of natural wetlands. We specifically studied the following sites: the coastal wetlands in the Petrosino area and the saltworks of Trapani and Paceco (both of them Ramsar sites, in the western part of Sicily), and the small mountain lakes in the Nebrodi Park, above 1200 m a.s.l., in the north-eastern part of the island. Here we assessed the impact of alien vascular plants on wild habitats, considering their ways of dispersal and colonization in the different geographic and anthropic contexts.