Paving the way for efficient seaweed cultivation

As we’ve learned before through close observation, indigenous knowledge and more recent scientific experimentation, nature’s diversity demands different approaches and has many lessons to show us.

It’s certainly true for seaweed.

As we forge a path for restoring our moana while developing a cost-effective industry for native seaweed species in Aotearoa, optimising cultivation methods is essential. The latest published report from our University of Waikato partners Rebecca Lawton and Marie Magnusson does just that.

The following is a summary.

Scientific research on aquaculture of the kelp Ecklonia radiata has so far focused on optimising non-living physical and chemical conditions like temperature and light in the hatchery, enabling year-round production of viable zoospores, and refining at-sea line configurations.

Yet key factors remain unexplored.

Two critical factors—seeding twine type and spore seeding density—can impact performance significantly.

Seeding twine type affects hatchery and at-sea success, but has rarely been examined for any seaweed species. Seeding density can also influence hatchery outcomes, affecting zoospore settlement, gametophyte growth, and sporophyte formation. Although spore density effects for Ecklonia radiata have been studied in petri dishes, applied research directly on twine remains lacking.

To address these key knowledge gaps, we conducted experiments to identify the optimal seeding twine type, twine diameter, and spore seeding density for Ecklonia radiata. Specific objectives were to test these factors’ impacts on seedling density and length during the hatchery period, and on at-sea coverage and growth post-outplanting. The study aimed to identify the twine type and seeding density that maximised hatchery success and initial at-sea growth, paving the way for efficient seaweed cultivation.

Key findings

Overall performance in the hatchery was best on polyester twine compared to kuralon and nylon twine, but two weeks after outplanting at-sea there were few differences between twines.

Based on the results of this study, we recommend using a seeding density of 2,500 spores mL-1 and polyester or kuralon twine with a small diameter (e.g., ~ 1mm) for cultivation of Ecklonia radiata to maximise efficiency and performance in the hatchery. The superior performance of polyester twine in this study contrasts with results of twine selection studies for other seaweeds

and highlights the importance of conducting species specific optimisation when developing cultivation techniques for new target species.

· R.J. Lawton and M. Magnusson, Effects of seeding twine type and seeding density on hatchery performance and initial at-sea cultivation performance of the kelp Ecklonia radiata, Algal Research (2024), https://doi.org/10.1016/ j.algal.2024.103777

The published report can be viewed here.