Socio‐ecological complexity in managing long‐standing invasive water hyacinth in wetland agriculture and fisheries

Abstract Managing long‐established invasive species in an ecosystem can be complex due to their multifaceted socio‐economic roles and use to the stakeholders, an issue requiring more attention. We measured the effects of water hyacinth ( Pontederia crassipes ), one of the world's most notorious invasive aquatic plants, on wetland agriculture, water quality and its use in destructive fish harvesting practices in Bangladesh. Stakeholder knowledge and perceptions regarding water hyacinth were also evaluated. Water hyacinth was recorded in 32% and 36% of surveyed plots in 2021 and 2022, respectively. Using a natural experiment similar to a Before–After–Control–Impact study design, water hyacinth presence was found to negatively impact yields of rice, wheat and jute. Controlling water hyacinth also increased farmers' costs. Water temperature, dissolved oxygen and transparency differed between areas with and without water hyacinth. Deployment of water hyacinth cover patches, constructed by fishermen, to encourage localised aggregation of fish, was associated with higher fish species richness and abundance by 54% and 263%, respectively. Fish caught by subsequent water drawdown were of all sizes and species, including several threatened species, reflecting the non‐selective method. It is currently unclear whether this method redistributes fish locally and captures a minor portion of the wetland fish production, but as it becomes more widespread, it poses an increasing threat to fishery sustainability. Local farmers, having limited knowledge about non‐native species, regarded water hyacinth as a natural component of the environment due to its presence for over a century in the country. While stakeholders recognised the negative effects of water hyacinth on crops, economically beneficial uses (efficient fish harvesting, as fertilisers and for jute retting) were also recorded. Our findings contribute to increased understanding that invasive species, especially those with long‐standing presence in ecosystems, can become deeply embedded in local socio‐ecological systems, blurring lines between ‘invasive’ and ‘naturalised’ categories. The dual role of water hyacinth as both an ecological disturbance and a socio‐economic resource represents a growing concern in tropical and subtropical regions, where complete eradication is often unfeasible and local communities have developed functional dependencies on the species. Read the free Plain Language Summary for this article on the Journal blog.