PHLOROTANNINS AS CHEMICAL DEFENSE AGAINST MACROALGAL EPIPHYTES ON ASCOPHYLLUM NODOSUM

Brock, E., Åberg, P., & Pavia, H. Department of Marine Botany, Göteborg University, Box 461, SE 40530 Göteborg, Sweden. Phlorotannins are a group of polyphenolic acids present in brown algae. They have been shown to act as defense against herbivores and UV-B radiation. They have also been suggested to function as a defense against epiphytes. In this study the effect of the presence of macroalgal epiphytes on the phlorotannin content in Ascophyllum nodosum was analysed. Six adult plants of A. nodosum were collected from each of four sites in the archipelago on the west coast of Sweden. Four apical parts from each of the 24 plants were analysed for their phlorotannin content. For each plant, two samples were without any visible macroalgal epiphyte growth and two samples were 50-100% covered by epiphytes, mainly of the orders Ceramiales and Ectocarpales. We were not able to detect any general effect of epiphytes on the phlorotannin content. There was, however, a significant interaction between the two factors algal individual and epiphytes, where apical parts with epiphytes present had either higher or lower levels of phlorotannin than samples without epiphytes. Furthermore, there was a general, significant difference in the phlorotannin content among sites. The results suggest that the relationship between macroalgal epiphytes and phlorotannin production in A. nodosum is complex and influenced by several interacting factors.