Who is Ostreopsis ovata? Ostreopsis ovata is an indigenous microalgae (size: 1000 times less than a mm!) composed of a single cell (unicellular). Arrived in the Gulf of La Spezia via ballast waters, this micro-algae is very well adapted to increasing seawater temperatures. To grow and reproduce, it requires strong light intensity, elevated temperature, high nutrient concentrations (nitrogen and phosphate salts) and calm water. Algae blooms (i.e., high concentration of algae) generally occur in summer, in shallow water, normally in protected basins (small natural bays and marinas). Where do we find this algae? O. ovata normally grows on rocks, macroalgae, corals, forming a brownish cover.

What’s going on in the bay? From half June 2022, seawater data recorded through Green Star project revealed, at 1 m of depth, temperatures reaching 24°C. In the same period, Ostreopsis ovata weekly samplings revealed a serious increase in algae concentrations in the bay. Thus, algae bloom is occurring one month in advance. Previous ENEA’s studies conducted in the Gulf of La Spezia report the start of Ostreopsis ovata growth in June, with a progressive increase in July until blooms normally occurring at temperature above 24°C. Such temperature has been recorded from half June 2022, thus allowing an anticipated bloom of this indigenous micro-algae.