Marine growth

Biofouling or biological fouling is the accumulation of microorganisms, plants, algae, or animals on wetted surfaces. Such accumulation is referred to as epibiosis when the host surface is another organism and the relationship is not parasitic.

Antifouling is the ability of specifically designed materials and coatings to remove or prevent biofouling by any number of organisms on wetted surfaces. Since biofouling can occur almost anywhere water is present, biofouling poses risks to a wide variety of objects such as medical devices and membranes, as well as to entire industries, such as paper manufacturing, food processing, underwater construction, and desalination plants.

Specifically, the buildup of biofouling on marine vessels poses a significant problem. In some instances, the hull structure and propulsion systems can be damaged. The accumulation of biofoulers on hulls can increase both the hydrodynamic volume of a vessel and the hydrodynamic friction, leading to increased drag of up to 60%. The drag increase has been seen to decrease speeds by up to 10%, which can require up to a 40% increase in fuel to compensate. With fuel typically comprising up to half of marine transport costs, antifouling methods are estimated to save the shipping industry around $60 billion per year. Increased fuel use due to biofouling contributes to adverse environmental effects and is predicted to increase emissions of carbon dioxide and sulfur dioxide between 38 and 72% by 2020.

A variety of antifouling methods have historically been implemented to combat biofouling. Recently, scientists have begun researching antifouling methods inspired by living organisms. This type of design imitation is known as biomimicry.

The variety among biofouling organisms is highly diverse, and extends far beyond attachment of barnacles and seaweeds. According to some estimates, over 1700 species comprising over 4000 organisms are responsible for biofouling. Biofouling is divided into microfouling — biofilm formation and bacterial adhesion — and macrofouling — attachment of larger organisms. Due to the distinct chemistry and biology that determine what prevents them from settling, organisms are also classified as hard- or soft-fouling types. Calcareous (hard) fouling organisms include barnacles, encrusting bryozoans, mollusks, polychaete and other tube worms, and zebra mussels. Examples of non-calcareous (soft) fouling organisms are seaweed, hydroids, algae and biofilm "slime". Together, these organisms form a fouling community.

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