Polyphenols in Tropical Brown Algae

BSc Honours Thesis Project
Supervised by: Craig R. Johnson

Many marine algae produce chemical defenses against herbivores. Polyphenols in brown algae exhibit the reverse of the general latitudinal trend evident in chemical defenses with temperate brown algae producing higher concentrations of polyphenols than their tropical counterparts. Polyphenols in tropical brown algae are not effective feeding deterrents of many coral reef herbivores. Polyphenol concentrations in brown algae on the southern Great Barrier Reef and their possible ecological role were studied. Polyphenol levels were found to be low (2% or less) in ten species of brown algae analyzed. Between-reef-zone variation in polyphenols correlated positively with the intensity of fish grazing in these zones. However bioassays conducted in the field at three sites, the reef slope, reef flat and lagoon gave no correlation between the amount consumed and the polyphenolic content of algae presented. Feeding trials conducted in aquaria with four common reef flat herbivores, using an analogous experimental design to the field bioassays, also showed no correlation between preference and polyphenol content. These results were further supported by feeding trials, where polyphenols were incorporated into an artificial (agar-agar) medium, using the same species of herbivores. Polyphenols in brown algae from the southern GBR are not likely to be an effective deterrent against herbivores. This is in accordance with previous findings from other tropical regions.

sargassum     sarg macro

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University of Queensland
Heron Island Research Station
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