Dietary effect of the boiled stipe of brown alga Undaria pinnatifida on the growth and gonadal enhancement of the sea urchin Strongylocentrotus nudus

In Miyagi Prefecture, the cultured brown alga Wakame (Undaria pinnatifida) is boiled and then salted for human consumption. The stipes are discarded. To explore a use for the discarded stipes, we studied their dietary value on the growth of the juvenile sea urchin Strongylocentrotus nudus and the gonadal enhancement of adults and compared them with that of fresh stipes, blades and sporophyll in the rearing experiment. Rapid growth in juveniles was most effectively promoted by the intake of fresh blades, with consumption of boiled stipes being next in value. The intake of boiled and salted stipe was higher than fresh stipe and sporophylls; however, sporophylls promoted the best gonadal enhancement in adults. Despite the low carbohydrate and crude protein content in boiled stipe, we estimated that boiled stipe could enhance the gonadal index by as much as 18%, the minimum level for market, after 5 months of feeding. The results suggest that boiled stipe would be an effective deterrent to the grazing intensity of the wild sea urchin within coralline flats where marine afforestation is being attempted.