Long-term phytoplankton abundance, structure and diversity in the eutrophic Cabras Lagoon (Italy, W Mediterranean Sea)

The Cabras Lagoon is a shallow and eutrophic Mediterranean lagoon, located on the west coast of Sardinia, in the Gulf of Oristano. It is one of the aquatic ecosystems listed in the station “n. 14 Marine ecosystems of Sardinia” of the Italian Network of Long Term Ecological Researches (LTER Italy). In Cabras Lagoon primary production is dominated by phytoplankton, that makes studies of this biotic component crucial to understand the ecosystem dynamics. The temporal variation of phytoplankton abundance, structure and diversity was analysed from 1999 to 2009 to assess the general features of phytoplankton succession and its long term tendencies in relation to environmental factors. The objective is to identify the main driving forces of phytoplankton variability in the light of the general trends of Mediterranean transitional waters. The pluriannual dynamic of phytoplankton composition showed important changes during the study years. A clear dominance of Bacillariophyceae was observed until the end of 2000. In this span of time also Nanoplankton and Dinophyceae were important. From 2001, the presence of Cyanophyceae increased, with strong affirmations especially in summers. The results demonstrated that the major phytoplankton biodiversity observed from the beginning of the study until 2002 coincided with a major temporal variability of all the considered environmental parameters, in particular of nutrients and salinity. The high stability of the same parameters for more than a year, permitted the persistent affirmation of Cyanophyceae from 2007 until 2009.