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 reported occurrence of this alga in Taiwan was dated 2005. To determine whether or not 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 ecological background examination and population genetic analysis. Our island-wide survey showed that this alga is widespread in the field in Taiwan, where the climate greatly differs from that of South America. Our population genetic analyses showed that the cox2-3 sequences were identical in all the samples of M. macrospora from Taiwan, consistent with our observations that the alga mainly expanded through asexual reproduction. Furthermore, our long-term ecological assessments and field observations revealed that M. macrospora can grow under a wide range of environmental conditions (e.g., temperature, pH, and light conditions), self-sustain for nearly a decade, and bloom in polluted waters. Taken together, these data suggest that M. macrospora has successfully invaded the freshwater ecosystems in Taiwan due to its ability to undergo asexual reproduction and to self-sustain under broad environmental conditions. We hope that our study brings attention to invasive freshwater algae, which have been overlooked in conservation planning and management.