Phytoplankton colonization patterns. Is species richness depending on distance among freshwaters and on their connectivity?

Phytoplankton assemblages in two Sicilian water bodies were compared to test the hypothesis that colonization events and the successful establishment of a new species in an aquatic ecosystem may depend on the number of water bodies in a given area and on their relative distance. The two ecosystems are both natural, shallow lakes and they are protected sites hosting a rich avifauna. Lake Biviere di Gela is located in an area with a high density of ponds, whereas Lake Pergusa is an isolated waterbody without other aquatic ecosystems in its surroundings. Both lakes had almost disappeared about 10 years ago because of the over-exploitation of their main inflows. They were therefore re-filled using water from other catchments and their phytoplankton has been sampled since their re-filling. The results show that Lake Pergusa has maintained a species-poor phytoplankton assemblage since its re-filling, whereas Lake Biviere di Gela has been showing progressively richer phytoplankton assemblages during time. The composition of samples collected in nearby located temporary ponds suggests that phytoplankton in this area belongs to a species-rich metacommunity which favored its re-establishment in the lake. Aquatic ecosystems conservation plans cannot thus neglect the role of small waters located in the catchments.