Biofouling Management

The possible introduction of invasive aquatic species (IAS) from biofouling is a potential threat to biodiversity. Biofouling accumulates on surfaces and structures immersed in or exposed to water and is often described as micro- or macro- fouling. Microfouling consists of microscopic organisms that create a slime layer whilst macrofouling forms a visible growth of plants and animals on the surface. To be considered invasive, the biofouling species must first establish itself on the surface of a ship, survive the voyage, reproduce or be dislodged, and then colonise a new habitat. Invasive species pose threats to human, animal and plant life, economic and cultural activities and the aquatic environment.

In July 2011, the IMO also adopted a set of guidelines to provide a globally consistent approach to managing biofouling reduction and the threat posed by IAS. In 2023, IMO adopted a revised set of guidelines to improve the uptake. The revised guidelines also recognise biofouling management as a means of improving a ship’s hydrodynamic performance, thereby reducing greenhouse gas emissions. There is therefore a strong economic, as well as an environmental incentive to manage biofouling well. In 2025, the IMO adopted guidance designed to help shipowners, charterers, operators, and seafarers on matters relating to in-water cleaning.

In 2026, the IMO initiated the development of a legally binding framework for the control and management of shipsʹ biofouling to minimize the transfer of invasive aquatic species. There are several key issues that will need to be addressed during the development of such a framework.

When formulating the global regulatory framework, serious consideration should be taken of the present severe shortage of inspectors if such inspectors are required to be both independent and certified in accordance with the 2023 Guidelines. Therefore, practical elements in connection with inspections are critical to the shipping industry.

Access to in-water cleaning will be essential under a global regulatory framework. Several countries have adopted local regulations prohibiting in-water cleaning and the number of ports permitting in-water cleaning continues to decline. At the same time the availability of experienced divers and suitable remotely operated underwater vehicles (ROVs) remains insufficient to support the introduction of a legally binding instrument.

Shipowners are regularly assessing the condition of the ship’s hull primarily through performance monitoring, which involves tracking indicators such as fuel consumption and speed loss. This analysis is rather complicated as other factors eg mechanical failures in the propulsion system can influence speed and fuel consumption. The relationship between performance monitoring for efficiency and biofouling will need to be better clarified. Also, standards such as ISO 19030, Measurement of changes in hull and propeller performance, will have to be updated to support the introduction of a new mandatory biofouling framework.

In October 2001, the International Convention on the Control of Harmful Anti-fouling Systems on Ships (AFS Convention) was adopted by the International Maritime Organization (IMO). It sets forth requirements to prevent direct adverse impact on the environment from use of anti-fouling systems on ships.

Anti-fouling coatings (AFC) will sustain damage when coming into contact with hard and heavy objects, including fenders, tugs, anchor chains or the seabed during low tide. This type of localised damage is typically minor relative to the total surface area of the ship and therefore is unlikely to result in a significant increase in the risk of introducing invasive aquatic species.