This month, our Offshore Kelp Mariculture project team successfully harvested giant kelp, Macrocystis pyrifera, from the Tinderbox kelp lease.

This major phase 1 project milestone comes just 6 months after the initial outplanting of hatchery-reared microscopic juveniles on 18m diameter rings and 60m grow lines. The team harvested 48m out of a total of 360m of grow line with the average plant size ranging from 1.6m to a maximum length of 3.4m in just 6 months.

In total, approximately 3.6 tonnes of Macrocystis has been grown at the Tinderbox lease.

The project, led by Associate Professor Jeff Wright and the University of Tasmania’s Institute for Marine and Antarctic Studies (IMAS), aims to review, design and trial offshore production systems for kelp mariculture and test the viability of kelp mariculture at commercial scales.

The lines consisted of three different cultivars to assess whether certain cultivars performed better than others. A range of measurements were taken to assess growth rates and performance, including wet and dry weight per metre of grow-line, density, size of plants, and tissue carbon : nitrogen ratio – a key indicator of kelp health.

The project team were excited to achieve such great results, with 1-2mm juveniles reaching 3.4m in this short period of time. Next week, the team will harvest Macrocystis at two additional sites at Tower Bay and Storm Bay.

Southern Ocean Carbon Company will remove the remainder of the kelp and grow lines at Tinderbox in December.

As project lead, Associate Professor Jeff Wright states,

“The growth achieved after only 6 months at the Tinderbox site is impressive and it is likely production will be higher at other sites. We now have routine optimised hatchery and grow-out methods for Macrocystis which provides great opportunities for growing Macrocystis in other projects and contexts such as in deeper offshore environments.”

Phase I of the project focused on engineering design, in-water testing of kelp growth, monitoring of impacts of the trial kelp farm infrastructure at a relatively sheltered site to test the viability of kelp mariculture at commercial scales.

The learnings and modellings taken from Phase 1 will help to inform site selection for phase 2 in deeper waters. Key learnings were taken along the journey, including sensitivity to light levels and temperature, therefore limiting the mariculture of giant kelp to 8-9 months each year is recommended to avoid warm summer periods with outplanting at 8-9m for offshore sites.

The project team will look to advance Phase 2 research to test the scalability and economic viability of offshore kelp mariculture that will work to achieve positive environmental outcomes, have a strong social license, and have the appropriate policy and regulatory frameworks in place.

For more information, videos and images visit the project page.