Golfo di Olbia - Italy

The Gulf of Olbia is situated on the eastern coast of Sardinia. Morphologically, it is a typical ria, long 5 km, wide 2 km and with a total area of 600 ha, a mean depth of 5 m and a maximum depth of 10 m. The gulf receives a freshwater flow from the Padrongianus River in its southern part. The town of Olbia, located in the inner part of the Gulf, is one of the most important passenger harbors in the Mediterranean (about 4 million passengers per year) with in addition a commercial and an industrial harbor. It is also the largest mussel- and clam-farming area in Sardinia (5000 t yr−1). Mussel and clam farming is strongly affected by the presence of toxic algae. Since the early 1990s, the Gulf of Olbia has been monitored with respect to its trophic state and phytoplankton abundance and composition, in particular, the presence of toxic or harmful species of genus Alexandrium (Dinophyceae). However, the first data were collected in 1987, in connection with a discoloration event due to phytoplankton and with an extensive fish death. A long-term series of data is available and derives from high-frequency measurements and samplings to assess environmental and biological parameters. In particular the data concern the main trophic descriptors (Secchi depth, temperature, pH, conductivity, dissolved oxygen and saturation, alkalinity, NH4-N, NO2-N, NO3-N, total nitrogen, soluble reactive phosphorus, total phosphorus, dissolved silica) and phytoplankton abundances, as chlorophyll a, cell densities and biomass, class and species composition. Data collection started in 1992 for only phytoplankton data, then, other environmental variables are added in 1996, with some time gaps of various sizes up to 2008. The collection of only phytoplankton data has continued without interruption since 2008.