Ballast Water and Biofouling

Ballast water and biofouling management prevents the spread of invasive marine species between regions through vessel ballast water discharges and hull biofouling (IMO, 2004; IMO, 2023). This may include, among others, compliance with the IMO Ballast Water Management Convention (BWM Convention), verification of ballast water treatment systems, in water cleaning protocols with containment, propeller and niche area cleaning requirements, risk assessments for high risk vessels, regional cooperation through marine pest networks, and monitoring of in port cleaning activities.

For DMC ports, ballast water and biofouling management can protect native marine biodiversity, prevent costly ecological damage from invasive species, safeguard aquaculture and fisheries, maintain ecosystem services, and support sustainable maritime trade (Costa-Areglado et al., 2025; GEF, UNDP and IMO, n.d.).

Ballast water, taken on by ships to maintain stability and trim, is one of the largest pathways for invasive marine species transfer globally. The IMO International Convention for the Control and Management of Ships' Ballast Water and Sediments (BWM Convention), which entered into force in 2017, requires ships to manage ballast water to reduce the transfer of harmful aquatic organisms and pathogens. Treatment technologies include, among others, filtration, ultraviolet disinfection, electrolysis, and chemical treatment.

Port State Control inspections verify vessel compliance with BWM Convention requirements, including valid ballast water management plans, international ballast water management certificates, and records of ballast water exchanges or treatment. Non compliance may result in vessel delays, mandatory treatment, or denial of ballast water discharge until compliance is verified.

Biofouling on vessel hulls is a second major pathway for invasive species transfer, with marine organisms attaching to hulls, niche areas (sea chests, propeller shafts, rudders), and ballast water uptake strainers. The IMO 2023 Guidelines for the Control and Management of Ships' Biofouling provide updated guidance on biofouling prevention and management (IMO, 2023). In water cleaning of vessel hulls can remove biofouling but may release invasive organisms and biocides; controlled in water cleaning is increasingly regulated under national frameworks; for example, in New Zealand in-water treatment of international vessels can only be carried out by approved treatment providers.

The Global Environment Facility, United Nations Development Programme, and IMO GloFouling Partnerships Project (December 2018 to May 2025) supported developing countries in strengthening biofouling management, including capacity building, policy development, and stakeholder engagement (GEF, UNDP and IMO, n.d.). A 2025 literature review of biological invasions via ballast water found that about 85% of published ballast water studies came from the northern hemisphere, limiting understanding of species transfers in other regions (Costa-Areglado et al., 2025).

Regional cooperation supports effective ballast water and biofouling management. The IMO 2017 Guidelines for Risk Assessment under Regulation A-4 of the BWM Convention (G7) include the same risk area concept, under which exemptions are subject to consultation and agreement between States that may be affected.