Adventitious branching as a herbivore-induced defense in the intertidal brown alga Fucus distich us

Adventitious branches are produced following lnjury in at least 5 specles of brown algae in the family Fucaceae. Field experiments showed that these structures can be induced in the intertidal brown alga Fucus distichus by mechanical damage to the plant apices. The mean number of adventitous branches on F. distichus and the percent of plants with adventitious branches was positively correlated with the density of littonne snails Ljttorina sitkana and L. scutulata near the plants at 8 locations within the main beach of Tatoosh Island, Washington, USA, suggesting that the production of these structures is a response to grazing by the snails. In laboratory feeding experiments, both L. sitkana and L. scutulata preferred normal meristematic tissue (apices) over adventitious branches. Thus. adventitious branches appear to funcbon as an herbivore-induced defense that protects newly produced tissues from damage by grazers. Neither L. s~tkana nor L. scutulata showed a preference for w n g s over adventitious branches. Concentrations of polyphenolic compounds were about 10 to 70 % higher in adventitious branches than apices but were 20 to 50 O/O lower than phenolic levels in wings.