Effects of temperature and N:P ratio on the invasion success of the cyanobacterium Raphidiopsis raciborskii

The tropical invasive freshwater cyanobacterium Raphidiopsis raciborskii , first recorded in Central Europe about two decades ago, is now a relatively widespread species, expanding its geographic range. Currently, however, there are no records of this species in Sweden. As a bloom-forming and toxin-producing species, future population growths of R. raciborskii could negatively affect local biodiversity and ecosystem services. Hence, there is an urgent need to understand the factors controlling its capability of establishment in Northern European lakes. We performed a laboratory experiment to study the competitive success of R. raciborskii when interacting with other phytoplankton from major taxonomic groups typically found in Scandinavian lakes (diatoms, green algae, and cyanobacteria). The experimental settings included three temperature conditions (17; 22; 26 °C) and three different nutrient conditions (N:P ratios 8:1; 16:1; 32:1). The experiment was performed in a semi-continuous culture setup to test the invasion success of R. raciborskii . Raphidiopsis raciborskii did not become the dominant species in any of the tested conditions; however, it was able to grow and maintain its biomass in all treatments, also in relatively low temperature (17 °C). Temperature played an important role in the phytoplankton community composition, especially for the cyanobacterial group. Raphidiopsis raciborskii was more successful than Planktothrix agardhii , but less dominant than Microcystis aeruginosa . Temperature is thus important in determining the potential survival and settlement of the invasive R. raciborskii in lakes.