Giving Laminarian kelps an edge: Exposure of nursery-reared juvenile kelps to enhanced water motion improves sporophyte growth and yield at-sea

Abstract

We investigated whether increased water motion in the nursery enhances growth and subsequent at-sea cultivation performance of juvenile kelp (Ecklonia radiata, Lessonia corrugata, and Macrocystis pyrifera). Two 42-day nursery experiments compared a traditional static nursery method (aeration-driven water motion) with a treatment in which spools were additionally rotated at ~4 cm s⁻¹. The first experiment used side lighting for rotating spools and overhead lighting for the static treatment, while the second experiment provided surrounding light to both treatments to isolate the effect of water motion from light orientation. Juvenile sporophytes from the first experiment were subsequently deployed at sea for ~5.5 months to assess growth and density. Enhancing water motion by rotating the spools significantly increased sporophyte length for all species in both nursery experiments without affecting sporophyte density. Significant flow-on effects were detected during the at-sea phase, with the rotating treatment resulting in higher yields, sporophyte density, sporophyte weight, and larger holdfasts. The holdfast contribution to total sporophyte weight following the rotating nursery treatment varied among species: higher in L. corrugata, unchanged in E. radiata, and lower in M. pyrifera. Species-specific differences were observed in all response variables except density during the at-sea cultivation phase. L. corrugata showed the strongest response in the nursery phase, while M. pyrifera demonstrated superior performance during at-sea growth. These findings demonstrate the benefits of conditioning juvenile kelps by increasing water motion in nurseries, and further highlight the importance of species-specific nursery protocols to optimise kelp aquaculture.