Effects of seeding twine type and seeding density on hatchery performance and initial at-sea cultivation performance of the kelp Ecklonia radiata

Optimisation of cultivation methods is crucial to enable development of an efficient and cost-effective industry for novel seaweed species. Therefore, we investigated the effects of seeding twine type and zoospore seeding density on hatchery performance and initial at-sea cultivation performance of the emerging kelp aquaculture target Ecklonia radiata. Spores were seeded at three densities (2500, 5000 and 10,000 spores mL⁻¹) onto three twine types with differing diameters (Kuralon™: ⌀ 1.2 and 2 mm, nylon: ⌀ 1 and 3 mm, polyester: ⌀ 0.9 and 2 mm) and maintained in the hatchery for 60 or 74 days before outplanting to a marine farm site. At the end of the hatchery period sporophyte length and overall spool quality were highest on polyester and Kuralon™ seeding twines compared to nylon twines and sporophyte density was highest on polyester seeding twine, but two weeks after outplanting there were few differences between twines. Both hatchery performance and initial at-sea cultivation performance were best at seeding densities of 5000 and 10,000 spores mL⁻¹ compared to 2500 spores mL⁻¹ for twines with a 60-day hatchery period, but there were few differences between seeding densities for twines with a 74-day hatchery period. Seeding twine diameter did not have any significant effects on hatchery performance or initial at-sea cultivation performance. We recommend using a seeding density of 2500 spores mL⁻¹ and polyester or kuralon twine with a small diameter (e.g., ~1 mm) for cultivation of E. radiata to maximise efficiency and performance in the hatchery. Future studies should compare at-sea cultivation performance over an entire growing season to assess any effects of twine type on final biomass yield. Contrasts in our results with those of twine selection studies for other seaweeds highlight the importance of conducting species specific optimisation when developing cultivation techniques for new target species.