Long-term phytoplankton signals in different Sardinian aquatic ecosystems (Mediterranean Sea)

"It is generally accepted that long-term series of ecological data are essential in improving our ability to distinguish natural changes from those induced by human activities, at local and global scales. Moreover, they permit to establish baselines to which to refer to assess future changes. The potential of such long-term data series can be further enhanced if data collected on several types of ecosystems are compared to find common signals. . This study reports the temporal variation of phytoplankton and the main environmental parameters in three different aquatic ecosystems belonging to the Sardinian sites of the Italian Network of Long Term Ecological Researches (LTER-Italy): Cabras Lagoon, Gulf of Olbia and Temo Reservoir. The collection of data started in the middle of eighties (Temo Reservoir) and in the middle of nineties (Gulf of Olbia and Cabras Lagoon). Initially all the three ecosystems were classified as eutrophic and they are dominated by phytoplankton, as main primary producer. The objectives of this work are I) to assess the general tendencies of phytoplankton in each site and II) to compare the results of each site with the others to assess the eventual presence of common trends, in relation of those observed in the Mediterranean basin.. Chlorophyll a showed a tendency to decrement in the three studied sites in the last years. In addition, the presence of Cyanophyceae has increased in the Cabras Lagoon from 2001, dominating all the other classes in the last years. This change was accompanied by the reduction of the cellular size class, a tendency observed also in the Gulf of Olbia. The LTER approach has permitted to observe decrements of Chl a and cellular size also in other Mediterranean sites, indicating the necessity of a deeper analysis of these possible common trends on the basin scale.. "