First observation of Raphidiopsis (Cylindrospermopsis) raciborskii (Nostocales) during a heatwave in Lake Comabbio (Northern Italy)

We report the first documented observation of the freshwater filamentous cyanobacteria Raphidiopsis raciborskii (synonyms Anabaena raciborskii, Cylindrospermopsis raciborskii) in Northern Italy, specifically in Lake Comabbio during July 2015. Previously, C. raciborskii blooms were observed in Central Italy and Sardinia. This species is considered an invasive and potentially toxic filamentous cyanobacterium, originally described as a tropical species, now spreading into temperate regions. It can produce toxins like cylindrospermopsin and saxitoxins, which pose a significant health risk to animals and humans. These toxins have been demonstrated to bioaccumulate in aquatic invertebrates, and they can lead to mass mortalities of fish and birds. The increasing intensity and duration of heatwaves, predicted to rise this century, create favorable conditions for harmful, bloomforming freshwater cyanobacteria.