Biofouling: Silent Hidden Menace Below Waterline

The maritime industry is currently plagued by a series of different problems, one of which is biofouling. Also known as “biological fouling,” biofouling has been a cause for concern in the maritime sector for decades, if not centuries, primarily due to its disruptive impacts on transportation and ocean logistics. That being said, marine biofouling has some far-reaching implications beyond these matters. For one, it presents a difficult challenge for industries in creating sustainable technologies, specifically in the marine renewable energy sector.

These maritime companies depend on submerged equipment to capture offshore waves, wind, and tidal energy. However, biofouling can make it hard to keep these pieces of equipment clean and operational. Basically, marine biofouling demands consistent maintenance of infrastructure and the use of specially designed materials for the protection of submerged equipment. For this reason, it is necessary to combat the effects of biofouling, and this begins by first understanding what biofouling exactly means and what its dangers are, specifically for the maritime industry.

What is Biofouling?

Biofouling is the accumulation of algae, plants, microorganisms, or tiny animals on wet surfaces with a mechanical function, thereby causing functional and/or structural deficiencies. There are essentially two types or phases of biofouling: macrofouling and microfouling. Macrofouling occurs when organisms, such as soft corals, seaweed, and barnacles, adhere to surfaces for the purpose of generating a fouling community. On the other hand, microfouling takes place when there is a formation of biofilm that attach to the surface.

Whether a surface is infected by macrofouling or microfouling depends on a couple of different factors. For one, temperature plays a substantial role in the accumulation of microorganisms since temperature influences the breeding periods and growth rate of marine animals. Aside from temperature, the other factors that can affect whether a surface is threatened by macrofouling or microfouling are geographical location, species diversity, and the amount of solar radiation present, which directly impacts photosynthesis.

The Dangers of Biofouling

Biofouling has brought problems to sea buoys and buoy moorings for quite several years. For some buoys, microfouling specifically results in an accumulation of ‘slime’ and other organisms on the solar panels, which impedes the power production of the buoys. The most significant risk is that these buoys can eventually run out of power and stop operating. Macrofouling, on the other hand, causes a much bigger problem for sea buoys. In this phase, organisms increase in weight and size, thereby altering the hydrodynamic volume of buoys and dragging them under the surface.

If a sea buoy gets submerged below the water surface, it will cease to function properly, thereby leaving scientists with incomplete and unreliable data. Now, the impact of biofouling on buoys is merely a small annoyance in comparison to its effects on the marine renewable energy sector. Not only does it cost a lot to clean surfaces routinely, but long-term maintenance and repair also usually require substantial investment. Particularly, macrofouling can result in corrosion from organisms that make use of endogenous compounds to attach to surfaces.

Similarly, maritime logistics and shipping companies face similar problems in vessel marine performance due to macrofouling, which can have long-term consequences on the environment. As reported by Nature Communications, an increase in roughness shown by a biofouling ship hull can lead to up to 86% of powering penalties at cruising speed. Even a relatively light biofouling on a ship hull by a diatom slime can already generate between 10% to 16% penalty. In the absence of effective and efficient anti-fouling measures that can maintain speed, fuel consumption and greenhouse gas (GHG) emissions will increase significantly.

Biofouling on Ships

All ships suffer from some degree of marine biofouling. Even those vessels that may have been recently maintained and cleaned or are incorporated with an anti-fouling system are still susceptible to biofouling on ships. According to a study conducted by Farrah Chan et al. in 2015, biofouling on ships is usually concentrated on niche areas, such as water-cooling systems, sea chests, and propellers, instead of on flat exterior surfaces on the primary hull. This is because hull biofouling is commonly well-managed by ship owners since biofouling can increase drag and consequently increase a ship’s fuel consumption.

Now, in a study done by Edith Arndt et al. in 2021, it was shown that the biofouling process starts within the first couple of hours of a vessel’s immersion in the water. Hull biofouling or biofouling on a ship can also be influenced by a variety of factors, such as the ship’s construction, particularly the design and location of its niche areas; its specific operating profiles, including parameters like ratio of time underway in comparison to time alongside and operating speeds; trading routes and places visited; and maintenance history, including the installation and operation of an anti-fouling system and the age, type, and condition of any anti-fouling coating.

One of the biggest risks of biofouling on ships is that it acts as a propeller for the relocation of invasive aquatic species. These species are introduced into new environments mainly by ships through hull biofouling. Indeed, marine biofouling is considered one of the primary propellers of bio-invasions since biofouling on ships that enter the waters of States may cause the settlement of invasive aquatic species, which pose threats to animal, plant, and human life; disrupt cultural and economic activities; and destroy the aquatic environment.

The Biofouling Guidelines

The potentially harmful relocation of invasive aquatic species through marine biofouling has been recognized by the International Maritime Organization (IMO), the Convention on Biological Diversity (CBD), the Secretariat of the Pacific Region Environment Programme (SPREP), the Asia Pacific Economic Cooperation forum (APEC), and a few UNEP Regional Seas Conventions. To combat the occurrence of such relocation, the IMO specifically began its anti-fouling efforts by formulating some related guidelines called the “Biofouling Guidelines.”

The Biofouling Guidelines were developed by the Sub-Committee on Bulk Liquids and Gases (BLG) as tasked by IMO’s Marine Environment Protection Committee (MEPC) for the purpose of reducing the relocation of invasive aquatic species due to biofouling. It was then supplemented by the “Guidance for Minimizing the Transfer of Invasive Aquatic Species as Biofouling for Recreational Craft,” which is for use by all operators and owners of recreational crafts that are less than 24 meters in length.

During the preparation of the Biofouling Guidelines, it was agreed that, as technological and scientific developments are made, the Guidelines are subject to alterations and refinements in order to allow the risk to be more sufficiently addressed. Coastal states, port States, flag States, and other parties that can aid in mitigating the issues associated with marine biofouling must exercise due diligence in implementing the Guidelines to the maximum extent possible, as it can play an essential role in lessening the risk of the relocation of invasive aquatic species.

To support this evaluation process, the IMO has come up with the Guidance for Evaluating the 2011 Guidelines for the Control and Management of Ships’ Biofouling to Minimize the Transfer of Invasive Aquatic Species, which aims to help Member States and spectators who wish to gather necessary information for undertaking evaluations of the Biofouling Guidelines and to do so in a more consistent way. Moreover, this Guidance identifies the kinds of performance measures that can assist in reviewing the different recommendations set out in the Guidelines. 

Finally, in furtherance of reinforcing the Biofouling Guidelines, the IMO Secretariat is actively undertaking various technical cooperation activities through its Integrated Technical Cooperation Programme (ITCP). These initiatives mainly have two objectives: First, they seek to raise awareness of the components and impacts of the relocation of invasive aquatic species through hull biofouling, and second, they aim to improve the public’s understanding and familiarity of the Guidelines in order to foster its international implementation and hasten the reduction of species invasions.


Marine biofouling is a disruptive phenomenon that causes serious problems in different industries, specifically the marine renewable energy sector and the maritime logistics and shipping industry. Besides destroying marine equipment and vessels, biofouling can destroy the aquatic environment and pose grave threats to plant, animal, and human life if not adequately addressed right away. For this reason, it is necessary for governments, international organisations, and private entities to work hand in hand in developing effective measures to combat biofouling. Ultimately, the fight against biofouling begins with awareness.

About Maritime Fairtrade

Maritime Fairtrade is an independent digital news platform that delivers the latest news about and updates on the Asian maritime trade. We are committed to providing extensive coverage of regulatory changes and profound analyses of emerging trends within the maritime sector.

Do not hesitate to check out our maritime guide in Singapore to remain well-informed about the most recent events in the industry. Apart from news and analyses, our website also provides a plethora of information on different aspects of the maritime sector, including recommendations for the most excellent shipping courses in Singapore.


The best maritime news and insights delivered to you.

subscribe maritime fairtrade

Here's what you can expect from us:

  • Event offers and discounts
  • News & key insights of the maritime industry
  • Expert analysis and opinions on corruption and more