Chemical defence

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Biofouling of living surfaces

Every surface in a natural aquatic environment is a potential site for a biofouling community. Bacterial colonization and formation of biofilms is generally followed by settlement and adherence of diatoms and protozoa followed by colonization by invertebrate larvae and algal spores. Chemical interactions play a major role in this development and in further maintenance of a biofouling community. Biofilm bacteria can for instance provide both positive and negative settlement cues for other bacteria and higher organisms. Fouling of the surface of sessile organisms is often disadvantageous for the host, for instance resulting in reduced rates of photosynthesis by shading of seaweeds, increased drag and thereby increased risk of being torn of the substratum, and by influencing the palatability of the host to herbivores/predators. Pathogenic bacteria can also cause severe tissue damage and even mortality. Consequently, many sessile plants and animals are believed to or have been shown to produce antifouling compounds. Several studies have for instance shown that red and brown algae (seaweeds) produce compound with inhibitory activity against bacteria [1] [2] invertebrate larvae [3] [4] and algal spores [5].

In order to assess whether a chemical compound has any ecologically relevant role, it is however important to know that the compound is present at the surface of the host organism, or is released into the surrounding water, at concentrations that deter the naturally relevant fouling organisms. One successful way to address this challenge is in manipulative studies by selective inhibition of the host organism production of the potential antifouling compound.

A schematic representation of manipulative studies of chemical defense
A schematic representation of manipulative studies of chemical defense

Examples of seaweed chemical defence

The chemical defence of the red alga Delisea pulchra has been intensely studied [1]. This seaweed produces metabolites known as halogenated furanones, which are stored in gland cells from where the substances are released to the surface of the seaweed at concentrations that inhibit fouling of bacteria, algal spores and invertebrate larvae. In the case of bacterial inhibition, the halogenated furanones interfere with a common bacterial signal system (N-acetylated homoserine lactones) thereby inhibiting growth of gram negative bacteria [5]. Similarly, the red alga Bonnemaisonia hamifera, commonly found in Skagerrak, has been found to produce chemicals which are stored in gland cells and that inhibit fouling of bacteria as well as of higher organisms at the concentrations found at the surface of the alga [6] [2].

Another example of chemical defence is where bacteria on the surface of a host organism inhibit further attachment and growth of other bacterial species or of higher organisms. This “housekeeping” mechanism has for instance been shown for bacteria found on the green algae Ulva lactuca. In this case a low abundance of these bacteria on the algal surface is sufficient to have potential to inhibit further fouling [7].


  1. Sridhar K.R., Vidyavathi N. (1991) Acta Hydrochim. Hydrobiol.19: 455-496
  2. Hellio C., Bremer G., Pons A.M., Le Gal Y., Bourgougnon N. (2000) Appl. Microbiol. Biotechnol. 54: 543-549
  3. Lau S.C.K, Qian P.Y. (2000) Biofouling 16: 47-58
  4. Schmitt T.M., Hay M.E., Linqvist N (1995) Ecology 76:107-123
  5. 5.0 5.1 Dworjanyn S. A., Wright J. T., Paul N. A., de Nys R. Steinberg P. D. (2006) Oikos 113: 13-22
  6. Nylund G.M., Cervin G., Hermansson M., Pavia H. (2005) Mar. Ecol. Prog. Ser. 302: 27-36
  7. Rao D., Webb J.S., Holmström C., Case R., Low A., Steinberg P. Kjelleberg S. (2007) Appl. Environ. Microbiol. 73: 7844-7852
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