The influence of phlorotannins and bromophenols on the feeding behavior of marine herbivores was
determined using bioassay of Turbo cornutus. It was found that phloroglucinol and its oligomers
isolated from the brown alga Eisenia bicyclis (eckol, fucofuroeckol A,
phlorofucofuroeckol A, dieckol, and 8,8’-bieckol) had a deterrent effect against feeding behavior of T. cornutus in the concentration of algal body, respectively. In the case of the examination of 0.1 mM
concentration, although fucofuroeckol A and phlorofucofuroeckol A significantly
reduced feeding by T. cornutus, phloroglucinol and
8,8’-bieckol did not show any significant
influence on feeding behavior, and eckol and dieckol had stimulating activity.
2,4-Dibromophenol and 2,4,6-tribromophenol, which are major components of
extracellular secretions from Eisenia and Ecklonia species, caused the
death, the torpidity, and the decreased appetite of T. cornutus at the concentration of 0.1 mM. In addition, 2,4-dibromophenol
had strong feeding deterrent activity at the concentration of 1 μM. These
results indicate that phlorotannins and bromophenols act as chemical defense
agents of brown algae against environmental stresses such as the herbivore attack.