The economic costs of invasive aquatic plants: a global perspective on ecology and management gaps

Protecting aquatic ecosystems requires comprehensive understanding and quantification of threats posed by invasive species to inform effective management strategy. In particular, aquatic invasive plants cause profound alterations to aquatic ecosystem composition, structure and productivity, however, monetary cost assessments have lacked at large scales. Here, for the first time, we synthesize the global economic impacts of aquatic and semi-aquatic invasive plants to describe the distributions of these costs across taxa, habitat types, environments, impacted sectors, cost typologies and geographic regions. We also examine the development of recorded costs over time across linear and non-linear models and infer the geographical gaps of recorded costs by superimposing cost and species distribution data. Between 1975 and 2020, the total cost of aquatic and semi-aquatic invasive plants to the global economy exceeded US$ 32 billion, of which the majority of recorded costs (57 %) was attributable to multiple or unspecified taxa. Submerged plants had $8.4 billion (25.5 %) followed by floating plants $4.7 billion (14.5 %), emergent $684 million (2.1 %) and semi-aquatic $306 million (0.9 %). Recorded costs were disproportionately high towards freshwater ecosystems, which have received the greatest cost research effort compared to marine and brackish systems. Public and social welfare and fisheries were the sectors most affected, while agriculture and health were most underreported. Cost attributed to management (4.8 %; $1.6 billion) represented only a fraction of damages (85.8 %; $28.2 billion). While recorded costs are rising over time, reporting issues e.g., robustness of data, lack of higher taxonomic resolution and geographical gaps (costly taxa currently occupying regions where monetary cost reports are lacking despite well-known impacts) likely have led to a dampening of trajectories. More robust and timely cost estimates will enhance interpretation of current and future impacts of aquatic invasive plants, assisting the long-term sustainability of our aquatic ecosystems and associated economic activities.