Phytoplankton dynamics in permanent and temporary Mediterranean waters: is the game hard to play because of hydrological disturbance?

Only few scientific investigations have been carried out, to our knowledge, on phytoplankton in Mediterranean temporary ponds. To test the hypothesis that climate forcing is the main factor affecting dynamics and structure of planktic algae in these peculiar ecosystems, and to assess the importance of human impacts on this basic component of the aquatic biota, phytoplankton structure and dynamics were analysed in two temporary, long lasting (9 months), ponds, and in a permanent one. The three studied water bodies can be classified as mesoeutrophic, which show extended macrophyte beds and are subjected to one or more human impacts, such as eutrophication, fish and plant introduction, and garbage pollution. Phytoplankton samples were collected monthly over two different periods in each pond. The identified phytoplankton taxa were grouped in functional coda and non-parametric ordination methods were used to analyse their annual patterns. Results showed a well-defined sequence of coda, which followed a common seasonal pattern in all the studied ponds, when the ordination techniques were applied to a singular water body. This pattern was overlapping in the three studied environments without apparent influence exerted either by the environmental typology (e.g. permanent or temporary) or by human impacts. However, when the analyses were carried out by means of a single matrix containing the coda shared by all the studied environments, they formed a cluster separating the single ponds rather than following common/overlapping seasonal patterns. The results suggest that local effects, particularly the specific composition and richness of phytoplankton assemblages, are as important as climate constraints.