How can chemical substances help sessile marine organisms to prevail? Are the substances they excrete of benefit to humans?

Biofilms
Have you ever been snorkelling in the sea? If so, you may have noticed a thin, often slippery layer, a so-called biofilm, often covering rocks and costal engineering structures. These films are, for example, composed of microalgae and bacteria. Have you been to southern areas, such as the Red Sea or Australia? If so, you have probably noticed that sessile organisms such as corals and sponges are usually not covered by such a biofilm. The same is true for macroalgae, seaweed or kelp, naturally occurring in our local waters. How do seaweeds, coral polyps and sponges manage not to be overgrown by microorganisms?

Chemical warfare in the sea
The answer is: Within the sea, a sort of chemical war rages. Many types of seaweed, invertebrates and other organisms, mainly sessile species, produce chemical agents, which they excrete into the surrounding waters. Scientists refer to these as secondary metabolites. These substances are called ‘secondary’ because they do not play a primary role in sustaining an organism’s metabolism. The secondary compounds may have a signalling effect. But they often also act as a kind of chemical weapon against bacteria, algae and fungi. These organisms do not tolerate such substances. They begin to become stunted, stop growing or even die.

Helpful Bacteria
At times, bacteria may help corals, sponges and others to survive. In such cases, bacteria living on the surface or within their host produce the protective substances. In return, the hosting higher organisms provide useful excretes or favourable living conditions. We can imagine this similar to the relationship between intestinal bacteria and humans:  Without these bacteria, many important nutrients that food contains would not be available for us. The so-called commensals, in return, find perfect conditions within our body that is only seemingly isolated.

Benefit to humans
Protective compounds affecting bacteria or rapidly proliferating cells of higher organisms are of interest to pharmacologists. If these substances can kill bacteria or fungi, they may also serve as a new form of antibiotics. Moreover, they may be able to stop the growth of cancer cells or even kill them. If so, a precursor for new cytostatic or anti-cancer drugs would be available. In fact, researchers’ worldwide search in the sea has already paid off. Other possible applications are biological coatings to prevent marine organisms growing on the ships’ hull.
At the ICBM, the research group Environmental Biochemistry, headed by Prof. Peter Schupp, deals with chemical ecological and molecular biological methods and issues surrounding the chemical ecology of the sea.