Animals and Money: Clingy crustaceans Cost the Shipping Industry Billions of US$

Maritime transportation is the cornerstone of global trade. According to a report from UNCTAD (United Nations Conference on Trade and Development), roughly 1200 billion tons of goods were transported by sea in 2022 [1]. This is equivalent to about 80% of the world´s trade volume. However, ocean shipping faces several challenges, one of which is the threat of barnacles. 

Many will recognize barnacles as small bumps with hard shells covering rocks by the sea, reefs, turtle shells, or whale skin [2]. Barnacles are crustaceans. As larvae they attach themselves to hard surfaces under water, where they then metamorphose into the barnacles as we know them with a hard shell covering their soft body [3]. They fuse themselves to surfaces by depositing and curing a multi-protein natural adhesive [4]. This special protein-based waterproof bioglue is usually called barnacles’ glue. When and where barnacles settle depends on various environmental cues that indicate suitable living conditions [3]. They will stay at this selected spot for the rest of their lives [5]. 

Barnacles not only attach to natural surfaces, they can also be found glued to the hulls of ships where they become a rather costly situation for the shipping industry. Barnacles sitting on the outside of a ship increase the ship´s surface roughness. This increases the frictional resistance of the ship in water, which leads to higher fuel consumption, decreased speed, longer voyages, and finally together leading to more fuel requirement. In the U.S. alone, the shipping industry may spend more than 30 billion US$ a year to overcome drag caused by marine creatures [6]. 

British Navy ships in temperate waters were estimated to experience a 35-50% increase in fuel consumption after six months of operating [7]. Assuming a 50% increase in fuel consumption, we can estimate the cost barnacles have for the worldwide trade of goods. A container ship at normal speed (20-25 knots or 37-46 km/hr) with a ship size of 8000 TEU consumes 225 tons of fuel per day [8]. The cost of a ton of fuel is around 700 US$ [9], costing the company 158.000 US$ a day. In this case, barnacles create an extra cost of around 79.000 US$ due to the additional drag. Now we assume that the entire amount of goods transported by sea in 2022 (1200 billion tons) was transported by such container ships. One 8000 TEU container ship can be estimated to carry a volume of about 87.000 tons [10]. In 2022 the trade volume per day would have been around 3,3 billion tons. To carry this daily volume, around 38.000 container ships would be necessary. Every day each container ship likely experiences an additional cost of 79.000 US$ due to barnacles, which was calculated above. For the year of 2022, barnacles would have created an additional fuel cost due to drag of roughly 1000 billion US$ for the entire trade volume moved by sea. 

Besides the additional expenses on fuel because of barnacles, removing them from ships is another costly matter. Hulls can either be coated early on to prevent barnacles from attaching or cleaned from barnacles. The cost of cleaning up so-called biofouling, including algae, barnacles and other shellfish, was estimated for ships of the U.S. Navy. The total cost for hull coatings, cleaning, and antifouling of a specific model of U.S. ships, which makes up 30% of US Navy fleet ships, is estimated at $56 million per year. Considering the entire U.S. Navy fleet, the approximate cost of hull fouling is between $180 and 260 million per year [11]. Cleaning costs can vary considerably depending on the size of ship, cleaning method and severity of biofouling. Scraping clean one square foot of hull surface can roughly cost 4,50 US$ [12], which would equal about 49,5 US$ per m². For the earlier example of an 8000 TEU containership, which likely has an underwater surface area of 16.644 m² [13], this would create costs of about 824.000 US$ per ship if the entire area needed cleaning. It is safe to assume that cleaning all shipping vessels from biofouling creates an additional cost for the industry in the range of multiple millions of US$.

Although barnacles might look harmless, these little creatures cost the shipping industry multiple billions of dollars to prevent, get rid of, or otherwise deal with. Despite the economic consequences we face because of the barnacle´s life cycle, we can also learn from them. The barnacles’ glue has been an area of research in bionics because of its strong adhesive properties underwater [14]. This substance that is a pain to shipping can be used as a tissue glue to quickly seal up wounds and help them heal [15]. What can we learn from this? There are always two sides to a coin.

Min Mao, Sophie Merz, Helen Rothfuß

Issue 25 (PDF)