Kelp that grows in the upper tidal zone, such as bladder wrack and knotted wrack, is especially rich in phlorotannins. But the concentration of the compounds varies considerably. Elisabet Brock has studied what influences this concentration and presents in her dissertation findings that show that dessication and exposure to UVB radiation, on the one hand, and, on the other, animals that eat algae affect the levels of phlorotannins in bladder wrack and knotted wrack.
Since bladder wrack and knotted wrack on the west coast of Sweden grow close to the waterline, they are exposed to environmentally varying conditions. Even though the tides only marginally affect the sea level, climate changes can create differences of up to two meters in the level of the seas. This in turn means that algae dry out, and without the protection of water the dry algae are exposed to stronger solar radiation.
As long as the algae are covered by sea water, the levels of phlorotannins increase in tissues, but when they dry out the chemical compounds are disseminated to the surface of the algae. If this is an active process, one of the functions of the phlorotannins could be to serve as a sun block, according to Elisabet Brock’s findings in her dissertation. If the compounds are also secreted into the sea, a further ecological effect could be to protect other organisms that are close to the surface from harmful radiation.
Phlorotannins have also been proven to have other ecologically interesting effects. The dissertation presents findings that show that phlorotannins in extracts have an inhibitory effect on the willingness of acorn barnacle larvae to take hold. This effect proved for the most part to be dependent on the concentration of phlorotannins, but also on what type of algae were tested. The findings thus indicate that phlorotannins should be interesting substances for use in the production of environmentally friendly paint for boat hulls.
Title of dissertation: Phlorotannins in Intertidal Brown Algae: Inducing Factors and Ecological Roles. The dissertation has been publicly defended.