Dinoflagellate cyst assemblages in three Mediterranean Lagoons (Sardinia, Italy)

"Lagoons, estuaries and wetlands are important components of the marine coastal zone. They mediate the transition from freshwater to marine environments. Coastal lagoons are often eutrophic or hypereutrophic systems because of their position at the ends of drainage basins. They are subject to extreme environmental fluctuations because they depend on the amount and frequency of exchange with the sea and, contemporarily, on freshwater inputs from surrounding catchments. Lagoons are highly productive areas that are often exploited for fishery and aquaculture. Both these activities and many of the ecological aspects of lagoon environments are vulnerable to damage caused by the proliferation of harmful algal species, which can be also the trigger for dystrophic events. About 75% of all harmful algal species are dinoflagellates, and a number of them produce resting cysts in their life cycles. Resting cysts can act as inoculum of bloom as well as a tool for species maintenance when conditions become unfavourable. Moreover, studies on benthic resting cysts can be very useful in describing the diversity of a particular area and in providing a more complete depiction of plankton composition. In the Mediterranean basin, very little is known about assemblages of dinoflagellate cysts in lagoons. The first results of a study on resting cysts carried out in three Mediterranean lagoons are here reported. Cabras, Santa Giusta and Corru S’Ittiri lagoons are located along the Western Sardinian coast (Gulf of Oristano) and they are characterized by differences in size, morphology, chemical-physical characters of the waters, trophic status and main primary producers. Cyst assemblages reflected these differences in the number of the observed morphotypes and in the composition. The lagoons shared a number of common cosmopolitan species (e.g. Scrippsiella trochoidea (Stein) Loeblich III). On the other hand, each lagoon hosted species not detected in the others: cysts of Alexandrium genus were detected only in Santa Giusta Lagoon; a new species was described from Corru S’Ittiri Lagoon; two morphotypes not yet described were observed from Cabras and Corru S’Ittiri lagoons. The study provided useful information on the presence of dinoflagellate species, increasing our knowledge on biodiversity of the lagoons. Particularly interesting was the finding of Alexandrium catenella (Whendon and Kofoid) Balech cysts in the Santa Giusta Lagoon enlarging the presence sites of this harmful species in Sardinia and in the Western Mediterranean Sea."