A multifaceted ecological assessment reveals the invasion of the freshwater red macroalga Montagnia macrospora (Batrachospermales, Rhodophyta) in Taiwan

Invasive freshwater macroalgae are rarely described. Recently, a freshwater red alga, Montagnia macrospora, was introduced from South America to East Asia via the global aquarium trade. The earliest occurrence record of this alga in Taiwan is dated 2005. To determine whether M. macrospora has become an invasive species in Taiwan and to understand its traits that facilitated its invasion, we took a total-evidence approach that combines examination of ecological background and population genetic analysis. Our island-wide survey showed that M. macrospora alga was widespread in the field across Taiwan, where the climate greatly differs from that of South America. Our population genetic analysis revealed that the cox2-3 sequences of all the specimens of M. macrospora from Taiwan were identical, consistent with the hypothesis that the alga expanded through asexual reproduction. Moreover, during our long-term ecological assessments and field surveys, we observed that M. macrospora is an ecological generalist that can self-sustain for a decade and bloom. Taken together, our data suggest that M. macrospora has successfully invaded the freshwater ecosystems in Taiwan due to its ability to disperse asexually and to grow under broad environmental conditions. We hope that our study brings attention to invasive freshwater algae, which have been overlooked in conservation planning and management.