Effects of hydrozoan colonization on biochemical compositions of the brown seaweed Saccharina japonica

Abstract

The stoloniferous hydrozoan Obelia geniculata frequently colonizes late harvested blade of the aquacultured brown seaweed Saccharina japonica. To understand harmful effects of the hydrozoans, we measured the tissue viability, proximate compositions, amino acid and fatty acid profiles, and metal contents of healthy blades, colonized blades, and hydrozoans isolated from the seaweed. Hydrozoans contained high amount of zinc (1.7 g/kg dry weight), which is 23% against the provisional tolerable weekly intake, at levels higher than the recommended range in food. In seaweed blades beneath the colony, after the removal of hydrozoans, levels of selenium, iodine, and docosahexaenoic acid increased, while copper, cadmium, nickel, chromium, and erucic acid levels decreased compared to healthy tissues. As evaluated for food or fodder, hydrozoans deteriorate the quality of seaweed, thus the epiphytic hydrozoans must be removed from the seaweed blade prior to its use.