Evidence of global dispersal of the harmful cyanobacterium, Raphidiopsis raciborskii, in lentic freshwaters through migratory waterbirds.

The cyanobacterium Raphidiopsis raciborskii has received much attention due to its global distribution and toxin production in freshwater. However, research on understanding the potential factors facilitating its geographical spread, the pattern of increasing range, and long-distance dispersal (LDD) of this species is very limited. In this study, we investigated the role of migratory waterbirds (using domesticated ducks as a proxy) and reservoirs (lentic waterbodies) in global distribution or dispersal of R. raciborskii. First, the global distribution of R. raciborskii under different reservoir scenarios was assessed through meta-analysis. The results showed a significant positive correlation between the global occurrence of R. raciborskii and the global number of reservoirs. Second, testing the capacity of R. raciborskii to spread via endozoochory or ectozoochory with ducks as a proxy of migratory waterbirds. The results indicated that R. raciborskii could be potentially dispersed through ectozoochory but not endozoochory, with a maximum carrying time of ∼96 hours corresponding to a maximum dispersal distance of ∼2300 km. In addition, the duck-carried R. raciborskii survived and could establish populations under suitable conditions. This study provides experimental evidence for the R. raciborskii dispersal through waterbirds. Overall, our results highlight that artificial reservoirs promote the increase of R. raciborskii populations, which could be dispersed across long distance via waterbird ectozoochory, thereby increasing the geographical range of R. raciborskii.