Effects of fertilization treatment and stocking density on the growth and production of the economic seaweed Gracilaria parvispora (Rhodophyta) in cage culture at Molokai, Hawaii
2003
Nagler, P.L. | Glenn, E.P. | Nelson, S.G. | Napolean, S.
The edible red seaweed, Gracilaria parvispora Abbott, was pulse-fertilized in tanks containing fish-culture water or chemical fertilizer, then cultured in floating cages in a low-nutrient, ocean lagoon in Molokai, HI. Small, daily additions of ammonium sulfate and ammonium diphosphate were the only additions needed to stimulate growth. Fish-culture water was as effective as chemical fertilizer in supporting growth. Thalli fertilized for 7 days in tanks contained 2.5-5% nitrogen in tissues by the end of the treatment period; upon transfer to low-nutrient water, nitrogen content decreased to 1% as the nitrogen was mobilized to support growth. Thalli grew rapidly over the first 14 days after transfer from fertilizer tanks to the ocean, achieving relative growth rates of 8-10% day-1 and producing 39-57 g dry wt. m-2 day-1. However, by 21 days after transfer, growth ceased due to depletion of stored nutrients. The optimal stocking density was 2 kg m-3 based on growth rates. Nearly all net growth occurred in the cages rather than in the fertilizer tanks, which serve only to introduce nitrogen into the thalli. The yields obtained here are four times higher than achieved previously with this species and are comparable to high-yielding, intensive tank cultures.
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