In addition to the ballast water of ships, biofouling is another significant vector for introduction and spread of non-indigenous species. Biofouling is the undesirable growth of underwater structures by microorganisms, plants, algae and animals. This applies in particular to ship hulls and niches.

Biofouling can lead to the establishment of invasive species which can pose a threat to human health, the environment or economic and cultural activities.

Every ship carries a certain amount of fouling, even if it has recently been cleaned or equipped with an antifouling system. The amount of fouling is influenced by a variety of factors:

  • Ship design and construction – in particular number, location and design of so-called niche areas,
  • the ship's operation mode – in particular factors such as operating speed and the ratio of sailing time to mooring time,
  • Regions the ship is visiting or staying in,
  • Ship maintenance – in particular type, age and condition of antifouling system, installation and operation of antifouling systems, cleaning techniques and dry dock handling.

Furthermore, biofouling increases surface roughness of the hull of the ship, which in turn increases the frictional resistance and, ultimately, fuel consumption and the associated greenhouse gas emissions as a whole.

IMO Biofouling Guidelines

The IMO Biofouling Guidelines (Guidelines for the Control and Management of Ships' Biofouling to Minimize the Transfer of Invasive Aquatic Species, Resolution MEPC:207 (62)) provide practical recommendations for measures that can help to minimize risks from biofouling. They are addressed to ship operators, shipowners, shipbuilders, shipyards, classification societies, manufacturers of antifouling systems, suppliers and other interested parties. The guidelines were adopted by the Marine Environment Protection Committee (MEPC) in July 2011. Biofouling Guidelines (MEPC:207 (62)) (PDF, 127KB, Not barrier-free file.)

The guidelines cover the following aspects, among others:

  • Biofouling management plan and report book,
  • Installation and maintenance of antifouling systems,
  • Underwater inspection, cleaning and maintenance,
  • Design and construction of ships.

Based on these guidelines, a further guidance was developed and adopted specifically for owners and operators of recreational craft with a length of less than 24 meters. This guidance provides additional information and recommendations for the procedure of land transport of boats. Guidance for minimizing the transfer of invasive aquatic species as biofouling (hull fouling) for recreational craft (MEPC.1/Circ.792) Guidance for minimizing the transfer of invasive aquatic species as biofouling (hull fouling) for recreational craft (MEPC.1/Circ.792) (PDF, 256KB, Not barrier-free file.)

The 2011 Biofouling Guidelines are currently revised by a correspondence group set up by the IMO sub-committee PPR. The first report of this evaluation and review process has reinforced the necessity of further revision of specific aspects of the guidelines. The correspondence group is expected to present their final report in 2023.

Another initiative by IMO to minimize the spread of invasive species through biofouling is the GEF-UNDP-IMO GloFouling Partnerships Project, which was launched in December 2018 and is running until the end of 2023. This project particularly supports the implementation of the IMO Biofouling Guidelines and promotes the development of best practices and standards for an improved biofouling management in other maritime industries such as aqua culture. The BSH is a strategic partner of GloFouling.

AFS Convention

The IMO Convention on Anti-Fouling Systems (AFS-Convention, International Convention on the Control of Harmful Anti-Fouling Systems on Ships, 2001) prohibits the use of harmful organotin compounds in antifouling systems on ships and stipulates a mechanism to prevent the use of other harmful products in antifouling systems. Tributyltin (TBT) and other highly toxic organotin compounds in antifouling paints have been banned since the convention entered into force in 2008. In 2021, MEPC approved amendments to include provisions for biocide cybutryne, which will enter into force on 1st of January 2023. From that date, ships may not apply antifouling systems containing cybutryne. Ships with an antifouling system containing cybutryne have to remove it or apply a coating or sealing coat to the antifouling system at the next scheduled renewal of the anti-fouling system after 1st of January 2023, however, at the latest 60 months after the application of the antifouling system containing cybutryne.

Effective antifouling systems are essential in shipping, as they not only prevent spread of non indigenous species, but also improve the hydrodynamic properties of ships, resulting in fuel savings and thus reduced transport costs and harmful emissions. Against this background, effective protection against fouling is equally in the interest of ship operators and the environment.

The development and testing of efficient but environmentally friendly antifouling strategies and systems is the subject of current research.

In-water cleaning

To minimize or limit the extent of biofouling on ships, biofouling management is usually implemented. A crucial part of this is in-water cleaning, which can be done proactively or reactively. As imported non-indigenous species in the biofouling as well as biocides and other particles from the AFS or Marine Growth Prevention Systems (MGPS) may be released into the environment during the in-water cleaning of ship hulls and niche areas, in-water cleaning bears certain environmental risks. Therefore, it is the intention to develop unified standards aiming at minimizing environmental risks.

As part of the EU-Interreg Project COMPLETE, the BSH in cooperation with other project partners developed a draft Biofouling Management Roadmap. Information on its status and options to perform in-water cleaning in ports and marinas of the Baltic Sea region as well as country-specific information on antifouling systems are provided in the BSH Biofouling Management Database.

During the subsequent project COMPLETE PLUS, the BSH developed a draft harmonised risk assessment method as basis for the approval of in-water cleaning of ships in the Baltic Sea area.

Biofouling Round table

After the BSH in cooperation with the German Shipowners' Association (VDR) first held a Biofouling Round table in 2019, the associated activities have continued steadily. The round table offers a platform for interdisciplinary exchange of information surrounding the topic of biofouling management for authorities, policy makers, the industry, associations, classification societies and research. An important aspect of the round table is to support the revision of the IMO Biofouling Guidelines.

Other advantages of biofouling management

Biofouling management practices can also improve the hydrodynamic performance of a ship, as the biofouling on the hull significantly increases the ship's resistance, which in turn effects fuel consumption as well as emission of air pollutants and greenhouse gases. Thus, biofouling management can be an effective tool for improving energy efficiency and reduction of air emissions from ships. This has been recognized by the IMO and is reflected in the 2016 Guidelines for the development of a Ship Energy Efficiency Management Plan (SEEMP) (only in german).

A ship's biofouling may potentially affect under-water noise levels generated by ships. An elevated ship's resistance may increase the engine output requiring increased propeller r.p.m. at constant speed. In addition, a rough propeller surface can increase cavitation and thus under-water noise. Further studies are required to shed light on the relationship between biofouling and under-water noise in the future.