Evaluating stakeholder awareness and involvement in risk prevention of aquatic invasive plant species by a national code of conduct

In 2010, Dutch stakeholders signed a code of conduct to prevent the introduction and spread of aquatic invasive plant species. This voluntary agreement between the government and horticulture sector (i.e. plant nurseries and retailers) has the objective to ban the sale of invasive species and to increase public awareness and stakeholder involvement in measures to prevent new introductions of potential invaders. Public outreach campaigns included flyers and posters displayed in stores and labelling of non-native plant species with warning logos and messages on harmful effects and appropriate disposal. We evaluated several measures issued in the Dutch code of conduct by performing ex ante and ex posterior surveys and interviews with relevant stakeholder groups. Compliance of retailers and producers concerning species on sale and proper labelling was monitored annually by the Netherlands Food and Consumer Product Safety Authority. Interviews with aquarists and water gardeners provided the first quantitative evidence in the Netherlands that 2-3% of these hobbyists deliberately introduced non-native aquatic plants in surface water. A survey of retail professionals identified limited availability of information and lack of salesman's knowledge on the species lists issued in the code of conduct as major impediments for their engagement. Furthermore, low frequency of meetings and lack of guidance were major obstacles identified by the partners assembled in the code of conduct. Overall, compliance to species bans showed promising results, however, problems were identified with correct labelling of species. We conclude by listing opportunities to improve voluntary regulations for preventing non-native species introductions.