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Effects of UV-B radiation and simulated herbivory on phlorotannins in the brown alga Ascophyllum nodosum

Journal article
Authors Henrik Pavia
Gunnar Cervin
Annelie Lindgren
Per Åberg
Published in Marine Ecology Progress Series
Volume 157
Pages 139-146
ISSN 0171-8630
Publication year 1997
Published at Botanical Institute,
Pages 139-146
Language en
Subject categories Marine ecology, Biological Sciences, Ecology


Models and experiments seeking to explain intraspecific variation in brown algal phlorotannins (polyphenolics) have mainly focused on the effect of 2 factors, herbivory and resource availability (carbon/nutrients). The possible importance of other biotic and abiotic factors, e.g. pathogenic micro-organisms, heavy metals and UV radiation, has often been suggested but only rarely experimentally tested. In the present study the effects of increased UV-B irradiance and stimulated grazing (clipping) on phlorotannin production in the brown alga Ascophyllum nodosum were investigated. The 2 treatments were applied simultaneously in a crossed factorial experiment in order to test for interactive, as well as separate, effects. Carbon and nitrogen content of the algae was also determined for each treatment. The effect of the experimental treatments on the feeding selectivity of a natural herbivore was tested in a subsequent feeding preference experiment with the crustacea Idotea granulosa. An increase (similar to 50%) in UV-B radiation during a 2 wk period resulted in a significant increase (similar to 30%) in mean phlorotannin concentration, while no significant changes in phlorotannin levels following simulated grazing were observed. The additional UV light caused a slight increase in the nitrogen content of the algae, indicating that the response in phIorotannin production was not caused by nutrient deficit. Absorption spectra of A. nodosum extracts, before and after removal of phlorotannins with polyvinylpolypyrrolidone, revealed that phlorotannins can contribute to absorption in the UV-B range (280 to 320 nn). The results imply that phlorotannins can function as inducible screens against harmful UV radiation. The grazer I. granulosa showed a clear preference for algae that had been exposed to an addition of UV-B radiation, in spite of their increased phlorotannin levels, supporting the notion that small marine herbivores in general are tolerant to chemical defenses of algae.

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