PHENOTYPIC VARIATION IN POLYPHENOLIC CONTENT OF THE TROPICAL BROWN ALGA LOBOPHORA-VARIEGATA AS A FUNCTION OF NITROGEN AVAILABILITY

Although brown algal phlorotannins have been shown to deter certain herbivores and may accumulate in response to herbivory, recent evidence has suggested that concentrations of these polyphenolic compounds are inversely related to nitrogen availability. Previous studies examining the relationship between brown algal phlorotannins and nutrient availability have been conducted in the field and, as a result, other variables may have contributed to observed variations in polyphenolic content. In order to more rigorously test the carbon-nutrient balance hypothesis, clonal isolates of the tropical brown alga Lobophora variegata were cultured for 4 wk in seawater media of 3 nitrogen concentrations (0.2, 1.2, 5.2 mg Nl(-1)). Total phenolic content was determined weekly by a micro-Folin-Denis assay which uses as little as 1 mg of tissue. Percent carbon and nitrogen (per dry weight algal tissue) were also determined weekly for each nutrient treatment. Significant differences (ANOVA, p < 0.001) in phenolic content were observed between nutrient treatments after 2 wk. Phenolic content was directly correlated with tissue C:N ratios and inversely correlated with percent tissue nitrogen. Our results support the hypothesis that nitrogen availability plays a role in determining phlorotannin concentrations in brown algae.