Distribution of three alien cyanobacterial species (Nostocales) in northeast Germany: Cylindrospermopsis raciborskii, Anabaena bergii and Aphanizomenon aphanizomenoides
Cylindrospermopsis raciborskii is considered a cyanobacterium of tropical origin and an alien species to temperate waters. However, it has been detected as far north as northern Germany. While previous studies have shown that all isolated German C. raciborskii strains are hepatotoxic, little is known about the spatial occurrence and relative frequency of this species in temperate Germany. The aim of this study was to investigate the spatial distribution and relative frequency of C. raciborskii close to its northernmost distribution limit, to characterise the habitat in which it is most likely to occur in this climatic zone and to search for any other neocyanobacterial species that might be present in German waters but has so far been overlooked. One hundred forty-two water bodies in northeast Germany were sampled from June until September 2004. All cyanobacteria species were analysed qualitatively and semiquantitatively. Besides C. raciborskii, two additional neocyanobacterial species were detected: Anabaena bergii and Aphanizomenon aphanizomenoides. For both taxa, these findings represent their northernmost occurrence and their first report from German waters. Cylindrospermopsis raciborskii was present in 27%, Anabaena bergii in 9% and phanizomenon aphanizomenoides in 7% of the samples. The occurrence of each species was analysed in relation to maximum lake depth, Secchi depth, lake volume and lake surface area. All three species were present in a wide range of habitats, but C. raciborskii and Anabaena bergii occurred significantly more often in shallow, turbid waters than in deep, transparent water bodies. None of the parameters investigated were significantly correlated with the occurrence of Aphanizomenon aphanizomenoides. In conclusion, alien thermophilic cyanobacterial species are much more widely distributed in temperate Germany than previously known. The results are discussed with respect to the possible mechanisms that enable these organisms to expand northwards.