Biofouling

The term fouling, or more specifically biofouling, is used to describe the growth and accumulation of living organisms on the surfaces of submerged artificial structures as opposed to natural surfaces. Concern over and interest in fouling arises from practical considerations including the enormous costs resulting from fouling of ships, buoys, floats, pipes, cables and other underwater man-made structures.

From its first immersion in the sea, an artificial structure or surface changes through time as a result of a variety of influences including location, season and other physical and biological variables. Fouling communities growing on these structures are biological entities and must be understood developmentally. The development of a fouling community on a bare, artificial surface immersed in the sea displays a form of succession , similar to that seen in terrestrial ecosystems, which culminates in a community which may be considered a climax stage. Scientists have identified two distinct stages in fouling community development: 1) the primary or microfouling stage, and 2) the secondary or macrofouling stage.

Microfouling: When a structure is first submerged in seawater, microorganisms , primarily bacteria and diatoms, appear on the surface and multiply rapidly. Together with debris and other organic particulate matter, these microorganisms form a film on the surface. Although the evidence is not conclusive, it appears that the development of this film is a prerequisite to initiation of the fouling succession.

Macrofouling: The animals and plants that make up the next stages of succession in fouling communities are primarily the attached or sessile forms of animals and plants that occur naturally in shallow waters along the local coast. The development of fouling communities in the sea depends upon the ability of locally-occurring organism to live successfully in the new artificial habitat . The first organisms to attach to the microfouled surface are the swimming larvae of species present at the time of immersion. The kinds of larvae present vary with the season. Rapidly growing forms that become established first may ultimately be crowded out by others which grow more slowly. A comprehensive list of species making up fouling communities recorded from a wide variety of structures identified 2,000 species of animals and plants. Although the variety of organisms identified seems large it actually represents a very small proportion of the known marine species. Further, only about 50 to 100 species are commonly encountered in fouling, including bivalve mollusks (primarily oysters and mussels), barnacles, aquatic invertebrates in the phylum Bryozoa, tubeworms and other organisms in the class Polychaeta, and green and brown algae.

Control of fouling organisms has long been a formidable challenge resulting in the development and application of a wide variety of toxic paints and greases, or the use of metals which give off toxic ions as they corrode. However, none of the existing methods provide permanent control. Furthermore, the recognition of the potential environmental hazards attendant with the use of materials that leach toxins into the marine environment has led to the ban of some of the most widely used materials. This has stimulated efforts to develop alternative materials or methods of controlling biofouling that are environmentally safe.

[Donald A. Villeneuve ]

RESOURCES

BOOKS

Workshop on Preservation of Wood in the Marine Environment. Marine Borers, Fungi and Fouling Organisms of Wood. Paris: Organization for Economic Cooperation and Development, 1971.

Melo, L. F., et al, eds. Fouling Science and Technology. Norwell, MA: Kluwer Academic, 1988.

Woods Hole Oceanographic Institution. Marine Fouling and Its Prevention. Annapolis, MD: U. S. Naval Institute, 1952.