Can Kelp Extract (KELPAK®) be Useful in Seaweed Mariculture?

Abstract

The addition of low concentrations of commercial kelp extract (Ecklonia maxima: Kelpak®) in addition to fertiliser has proven to be beneficial in agriculture. It triggers rooting in field crops, increases yields and has other useful effects, such as parasite reduction. Its efficacy has been attributed to the fact that Kelpak® is produced by a cold process, and is a high auxin/low cytokinin product. The aim of this study was to investigate if seaweeds (which do not have a root system) grown in culture systems, would benefit from the addition of Kelpak® or a combination of Kelpak® and fertilizer. A preliminary laboratory experiment was carried out by growing excised 15 mm tips of the red alga Gracilaria gracilis in culture dishes containing Provasoli Enriched Seawater medium to which various concentrations of Kelpak® were added. Gracilaria tips in some of the Kelpak® treatments (1:2500; 1:1000; 1:500) grew significantly better than the control. Further experiments were carried out on a pilot commercial scale at Jacobsbaai Sea Products Ltd. on the South African west coast. Ulva lactuca was grown in effluent from fish (turbot) culture, with additions of 1:5000, 1:2500 and 1:500 concentrations of Kelpak® once a week. The intermediate Kelpak® concentration (1:2500) produced the highest growth of Ulva in the turbot water, while the highest Kelpak® concentration (1:500) inhibited Ulva growth. In another Ulva experiment, various combinations of aquaculture effluent water, commercial fertiliser and Kelpak® at 1:2500 were used. Best growth of Ulva was obtained in turbot water containing both fertiliser and Kelpak®. The results suggest that Kelpak® could be useful in commercial seaweed mariculture operations.