Species traits have been used extensively in invasion science, providing common metrics across taxa and ecosystems that enable comparisons based on the functional responses and effects of biota. However, most work on traits in invasion science has focused on terrestrial plants, despite the vulnerability of aquatic ecosystems to invasive species, such as invasive seaweeds. Research that focuses on individual species of invasive seaweeds has intensified in recent years, yet few studies have synthesised the information learned on species traits to identify commonalities or knowledge gaps in invasion science. Through a systematic review of 322 papers that investigate the traits of seaweed species from across the globe, here we ask – what are the trends and gaps in research that investigates traits of invasive seaweeds? To address this question, we aimed to: (1) identify publication rates and characteristics of the studies examining traits of invasive seaweeds; (2) clarify which and how many species have been investigated; and (3) assess which traits have been measured and how those traits have been used. Our review revealed that study regions for research on invasive seaweed traits were concentrated in Europe and North America. In addition, we found a total of 158 species that have been investigated, with a large proportion of studies (35%) focusing on just two species, Sargassum muticum and Undaria pinnatifida. Our study revealed that the most researched traits were morphological, which were used to address a wide range of research questions. Key research gaps included relatively few studies from Africa, Asia and South America, a lack of papers researching more than one species and a lack of measurements of biomechanical traits. Altogether, this review provides a thorough overview of research progress on species traits of invasive seaweeds and highlights the existing knowledge gaps that may lead to new ways in which the traits of invasive seaweeds can be used to answer important ecological questions.
