IMPACT OF ENVIRONMENTAL CHANGES ON PRODUCTION OF BROWN ALGAL PHLOROTANNINS

Targett, N. M. Graduate College of Marine Studies, University of Delaware, Lewes, DE 19958 USA Ecological theories such as resource availability theory (e.g. carbon-nutrient balance hypothesis) and growth differentiation balance theory have attempted to provide a theoretical framework in which to balance putative improvements in plant fitness resulting from secondary metabolite production with the metabolic costs of these compounds. However, experimental tests of these theories have yielded mixed results, in part because they have relied upon static measures of phlorotannin concentrations and have incorrectly assumed phlorotannins to be immobile defenses with negligible rates of turnover. To test these theories more effectively, in situ rates of phlorotannin biosynthesis were examined in several species of brown algae as they responded to manipulations of their surrounding environmental conditions (light, nutrients, and simulated herbivory). The rates of phlorotannin synthesis measured for damaged Fucus vesiculosus from Maine (USA) were dramatically in-creased relative to controls. Carbon resources required for this response were supplied via wound-induced increases in photosynthetic rates, rather than changes in patterns of internal resource allocation. The lack of internal resource trade-offs indicates that phlorotannin production may not always generate allocation costs in these plants. Shading decreased the magnitude of the induced response but growth vs. defenses trade-offs were not identified. For Sargassum hystrix var. buxifolium from the Bahamas, rates of phlorotannin synthesis and total phenolic contents were decreased by both shading and nutrient enrichment. Overall, rates of phlorotannin synthesis were often, but not always, correlated with the eventual changes in total phlorotannin concentrations. Where synthesis and accumulations were uncoupled, differential rates of phlorotannin turnover are expected.