EXPERIMENTAL-EVIDENCE FOR THE EFFECTS OF POLYPHENOLIC COMPOUNDS FROM DICTYONEURUM-CALIFORNICUM RUPRECHT (PHAEOPHYTA, LAMINARIALES) ON FEEDING RATE AND GROWTH IN THE RED ABALONE HALIOTUS-RUFESCENS SWAINSON

The effects of polyphenolic compounds from brown algae on grazing and growth rate of the California red abalone Haliotis rufescens Swainson were examined. Abalone consumed three phenolic-poor algal species, Lam inaria sinclarii (Harvey) Farlow, Macrocystis pyrifera Agardh, and Ner eocystis luetkeana Postels et Ruprecht (mean phenolic content = 0.52% dry mass), at a greater rate than two phenolic-rich species, Dictyoneu rum californicum Ruprecht and Cystoseira osmundacea Agardh (mean pheno lic content = 4.60% dry mass). This inverse relationship between pheno lic content and consumption rate also existed after the algae were mac erated and the liquid portion of the blended slurry incorporated in ag ar discs. However, the correlation between grazing rate and phenolic c ontent improved in this latter experiment, thus suggesting that abalon e grazing was deterred significantly by the morphology of L. sinclarii and, to a lesser extent, of M. pyrifera. Polyphenolics extracted from D. californicum reduced abalone grazing rates by 90% when incorporate d into agar discs at a concentration of 6 mg.ml-1. Although abalone we re unable to maintain body mass when fed ad libitum on macerated M. py rifera incorporated into agar discs, polyphenolics from D. californicu m further inhibited shell growth when added to the discs at 5 mg.ml-1. The abalone ate less of the phenol-containing discs than of the discs lacking phenolics. Our results support findings of several prior stud ies that polyphenolic compounds from brown algae deter grazing by coas tal zone herbivores in the northeast Pacific Ocean.