Polyphenols from two brown algae, Fucus vesieulosus (L.) and Ascophyllum nodosum (L.) Le Jolis, inhibited feeding by the herbivorous snail, Littorina littorea. The active compounds were characterized as phloroglucinol polymers with a wide molecular weigh t range (mol wt 300,000) by spectroscopic, ultrafiltration, thin-layer chro- matographic, and chemical degradation data. As little as I% (dry wt) polyphenol in food reduced feeding by more than 50%, and polyphenolic extracts inhibited feeding entirely when present in concentrations of 2-5% (dry wt). Commercially available phloroglucinol dihydrate and gallotannin, which are known herbivore feeding deterrents in terrestrial plants, inhibited L. littorea feeding when added to food media in concentrations similar to those above. We conclude that polyphenols in F. vesiculosus and A. nodosum are functionally similar to terrestrial plant polyphenols (tannins) in providing chemical defenses against herbivores. This research is the first demonstration that chemical compounds defend these two dominant, perennial marine algae from the major herbivore found in their community.
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