This special issue of Aquatic Invasions presents papers from the 21^st International Conference on Aquatic Invasive Species (see editorial) and related research.

Thirty-five years after their initial discovery, Dreissenid mussels continue to spread and impact North American freshwater ecosystems. This study shows what happens when Dreissenids begin to explore water bodies at the edge of their temperature tolerance.

Another study compared the movement speeds of zebra and quagga mussels as one possible explanation for the ongoing shift from zebra- to quagga-domination in many freshwater systems.

Molecular researchers have been studying the Dreissenid invasion since its inception, and this study leveraged old and new samples to explore the complex shifts in population genetic structures of zebra and quagga mussels over time.

Simulations from British Columbia suggest that the impact of Dreissenid invasions will vary between different recreationally important fish species, depending on their exposure to the lake ecosystem.

The Chinese mystery snail is widely established in North America and parts of Europe. Species distribution models, as used on the species in Nova Scotia, Canada, may help managers identify priority areas for survey and management before the invasion is widespread.

Research from Brazil looks at the role of marine sponges as preferred habitats for invasive brittle stars and suggests that a lack of strong preferences may enable the invader to become widespread in Brazil.

According to this study, the snowflake coral has become widely established across Ecuador. Monitoring and mitigation programs are urgently needed to avert a growing risk of ecosystem damage.

Invasions by micro-organisms are understudied, since microbes are, by nature, less obvious than macroinvasive species. This research from Chilean Patagonia looked at the role of bacterial diversity in the spread of the invasive benthic diatom Didymosphenia geminata.

Assumptions of the Hardy-Weinberg principle of constant allele frequencies are violated by asexually reproducing species, like some variants of hydrilla. However, this study shows that the tool can still be useful for understanding the evolution of herbicide resistance in such species.

Understanding factors that drive the local occurrence of invasive plants is critical for effective mitigation and management. This study looked at natural and manmade factors that favor species presence in Brazil.

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