Optimisation of gametophyte culturing and seeding methods for cultivation of the kelp Ecklonia radiata

Abstract

Identification of optimal gametophyte culturing and seeding methods is essential for the development of kelp aquaculture for novel target species. We investigated the effects of light colour (red, white), light intensity (5–60 μmol photons m⁻² s⁻¹) and initial gametophyte density (0.005–0.25 g DW L⁻¹) on gametophyte growth and reproductive success in Ecklonia radiata; and the effects of seeding density (0.025–0.090 mg DW m⁻¹ twine), biomass state (vegetative gametophyte, microscopic sporophyte), and seeding method (spray, spray+rub, xanthan binder, alginate binder) on sporophyte density, growth and attachment strength on seeding twine in three laboratory experiments. We found pronounced and significant differences in the growth and reproductive success of E. radiata gametophytes in free floating cultures maintained under different light colours, light intensities and stocking densities. We also found substantial and significant differences in sporophyte density, growth and attachment strength among seeding methods, seeding densities and biomass states for hatchery seeding of twine. Based on our results we recommend maintaining gametophyte cultures under red light at an intensity of 20 μmol photons m⁻² s⁻¹ and a density of 0.025 g DW L⁻¹ to maximise vegetative growth, while successful reproduction can be induced within two weeks by placing cultures under white light at 20 μmol photons m⁻² s⁻¹ and a density of 0.005–0.05 g DW L⁻¹. For hatchery seeding and cultivation, we recommend spraying vegetative gametophyte biomass onto seeding twine at a density of 0.090 mg DW m⁻¹ twine. There was no advantage to using binders or inducing reproduction in biomass prior to seeding.