Phytoplankton colonization patterns and the abundance of suitable aquatic ecosystems: the importance of nestedness among freshwaters. 17th Workshop of the International Association of Phytoplankton Taxonomy and Ecology (IAP). Kastoria, Greece, 14-21 September 2014. Book of Abstracts: 34

Species-poor and species-rich phytoplankton assemblages in two Sicilian water bodies (Lake Pergusa and Lake Biviere di Gela) were compared to test the hypothesis that the number of colonization events and the successful establishment of a new species in an aquatic ecosystem may depend on the number and nestedness of water bodies in a given area. The two ecosystems are both natural, shallow lakes and they are protected sites hosting a rich avifauna. Both the lakes had quite high conductivity values (> 2,500 μS cm-1) and both were re-filled with fresh waters (< 400 μS cm-1) after they had disappeared because of the over-exploitation of their main inflows to fulfill agriculture water-demand. However, the Lake Biviere di Gela is located in an area with a high density of temporary ponds, whereas Lake Pergusa is an isolated water body without other aquatic ecosystems being present in its surroundings. Both the water bodies have been sampled for phytoplankton since their re-filling occurred in 2002 (Lake Pergusa) and in 2005 (Lake Biviere di Gela). The results show that Lake Pergusa has a quite species-poor phytoplankton assemblage with periods characterized by the virtual absence of species, whereas Lake Biviere di Gela show a very rich phytoplankton and a quite high rate of floral change from year to year. The composition of phytoplankton samples collected in the nearby temporary ponds suggests that Lake Biviere of Gela and the temporary pond system in its surrounding form a single reservoir of biodiversity which favored the quick re-establishment of a highly diversified phytoplankton in the lake. Conversely, the isolated Lake Pergusa, although its re-filling occurred three years earlier than Lake Biviere di Gela, still shows a very species-poor phytoplankton assemblage and very little inter-annual changes in its composition.