ROLE OF POLYPHENOLIC MOLECULAR-SIZE IN REDUCTION OF ASSIMILATION EFFICIENCY IN XIPHISTER-MUCOSUS

Feeding deterrent effects of polyphenolic compounds from both terrestrial and marine environments have been well studied. However, the effects of this compound class on herbivore digestion and assimilation are less well known, particularly with respect to marine herbivores. This study found that the reduction of assimilation efficiency in Xiphister mucosus, a marine herbivorous fish, fed algae treated with marine polyphenolics (phlorotannins) was affected by phlorotannin molecular size (mass). In general, phlorotannins > 16.60 x 10(-21) g > 10 kDa) significantly decreased the assimilation of X. mucosus; those <8.30 x 10(-21) g < 5 kDa) rarely, if ever, had an effect. To determine the ecological relevance of these findings, phlorotannin molecular size profiles were completed for several temperate and tropical brown algal species. In all but one of the algal species examined, the phlorotannins were concentrated in the > 16.60 x 10(-21) g size range. Thus, the size range of phlorotannins that significantly reduced assimilation was also the size range in which they were most concentrated. This work supports the idea that polyphenolics as a chemical class do not all have the same bioactivity, but differ in their activity in a size-dependent manner. It also addresses some of the discrepancies seen in feeding-preference studies, providing an alternative explanation for results.