Farmed kelp to balance nutrients

The success of native kelp propagation offers new cropping opportunities and broader environmental benefits

By Catherine Norwood

Photo of Giant KelpGiant Kelp or Macrocystis pyrifera grown on longlines adjacent to salmon cages at Okehampton Bay October 2018. Photo: Stefan Andrews

Thanks to the adaptation of seaweed aquaculture techniques to native kelp species, seedlings can now be reliably produced in hatcheries. This is providing the foundation for trials to cultivate native kelp in pursuit of commercial and environmental benefits.

Tasmania’s largest Atlantic Salmon producer, Tassal, is investigating the potential of native kelp plantations on its aquaculture leases, with trials adjacent to fish pens at several of its south-eastern production sites.

Kelps could potentially help offset increased nutrients in the water as a result of Atlantic Salmon production, says Craig Sanderson, a marine biologist who has been leading Tassal’s research in this area for the past three years. This method of combining complementary marine crops is known as integrated, multi-trophic aquaculture.

In particular, kelps could take up nitrogen generated as part of the process of fish farming. The additional nitrogen would help boost plant growth, reducing the environmental footprint of fish farming – a key element of Tassal’s broader eco-aquaculture program. Craig Sanderson says it is the lack of biologically available nitrogen that most commonly limits the growth of kelps and seaweeds in general.

His earlier research indicated that nitrogen originating from fish pens is quickly dispersed in the water column. It is difficult to detect any elevation in nitrogen levels more than 100 metres down-current of fish pens.

“So if kelp is grown next to pens, the front few rows might benefit from additional nitrogen, but as you move further away there would be less benefit,” he says.

Tassal therefore has a broader focus on maintaining the nitrogen balance across larger areas, such as the D’Entrecasteaux Channel as a whole, rather than just growing kelp immediately adjacent to Atlantic Salmon pens. Atlantic Salmon farming operates in the D’Entrecasteaux Channel under a nitrogen cap to prevent nitrification issues in the waterway. The Tasmanian Government has set the cap based on research from the CSIRO, funded by the FRDC. The research determined that land-based sources of nitrogen were also a significant source in conjunction with aquaculture and naturally occurring nitrogen inputs, such as cooler waters.

Seaweed production in the channel as part of aquaculture operations could help take up nitrogen and maintain the nitrogen balance for the channel as a whole.

Giant Kelp the stand-out

Of more than 1000 seaweed species native to Tasmania, just three have been identified by Craig Sanderson as potential candidates for Tassal production: Giant Kelp (Macrocystis pyrifera), Golden Kelp (Ecklonia radiata) and Tasmanian Kombu (Lessonia corrugata). All three are brown seaweeds with existing markets.

The seaweeds are closely related to the Japanese species Wakame (Undaria pinnatifida) and Kombu (Laminaria japonica). These are widely cultivated throughout Asia, usually on longlines – a technique Tassal is adapting to the native seaweeds.

Craig Sanderson says work over the past three years has identified Giant Kelp as the frontrunner for larger-scale production trials.

Giant Kelp is the most easily cultivated and fastest growing of the three species. It has existing markets for human consumption, for the production of alginates, in fertilisers and in aquaculture feeds. It is also being assessed as a potential source of fucoidan – an antioxidant and anti-inflammatory chemical extracted for use in nutraceutical products.

Propagation

During the past year, an FRDC-funded project has helped to refine the techniques used to produce kelp plants from spores for cultivation.

Kelps have a microscopic stage in their life cycle, known as the gametophyte. Gametophytes can be grown in the laboratory in flasks almost indefinitely by keeping them under red lights. Culturing this stage therefore provides an ongoing supply of seed stock, as an alternative to searching for plants in their reproductive phase in the wild.

The project’s aim is to grow the gametophyte stage of all three species. Blue light or white light can be used to trigger reproductive development and the release of sperm and eggs, which give rise to new plants.

These reproductive techniques have been established by researchers led by Catriona Hurd at the Institute for Marine and Antarctic Studies at the University of Tasmania. Cameron’s Oysters provided the original hatchery facilities for Tassal’s early trials, but last year the trials moved to the Spring Bay Seafoods facilities at Triabunna.

The kelp is seeded onto either one-millimetre or three-millimetre twine, which is then wound around 20-metre lengths of 12-millimetre rope. The ropes are set into the water attached to longlines in a process similar to that used in mussel production.

For the past three years, kelp has been set out on longlines at sites including Okehampton Bay, D’Entrecasteaux Channel, Port Arthur and Dover throughout the year to determine the best time for outplant.

Currently March and April appear to be the best times to take advantage of winter and spring growth. Summer planting trials demonstrated minimal production and were subject to fouling and nutrient stress.

Craig Sanderson says this means it is more likely that new crops will be set out each year and harvested line and all, rather than ongoing cutting of kelp growth. Harvesting is expected to occur in October when the plants are at their peak.

The 2018 trial mostly used two different subspecies of Giant Kelp. One has come from northern Tasmanian waters, which Craig Sanderson may indicate it is more tolerant of warmer water conditions.

Both subspecies successfully produced a harvestable quantity of seaweed. Tasmanian Kombu was also successfully cultivated this year on longlines, albeit in small quantities.

“We’re confident in the hatchery stage, and in setting the kelp at sea,” Craig Sanderson says. “We’re now at the stage of managing the crop to optimise growth and the quality of the product.”

“We’ve been learning what sort of conditions are the best to grow the seaweeds in, what the best way to put them out to sea is, [and] how they behave at the various sites, each of which has different growing conditions and potential problems.”

Among these problems have been warm water temperatures, big swells, and flushes of freshwater affecting growth. Wild mussels and other epiphytes have colonised some of the kelp longlines, smothering the plants. And when the kelp plants are seeded too densely onto the lines, they compete with each other for nutrients and light, reducing overall harvestable growth.

A farm-scale trial designed to produce commercial quantities of seaweed for specific markets is now proposed for 2019.

“Nitrogen uptake is one benefit for Tassal, but the seaweed will also need to pay for itself as a crop,” Craig Sanderson says.

As part of the FRDC-funded work, Deakin University will conduct a nutritional analysis of the kelp produced during 2018, which will help determine potential markets. Heavy metal content will be determined, as well as naturally occurring iodine and inorganic arsenic; two elements of particular concern in seaweeds generally.

All Tassal’s trials are undertaken within the company’s lease areas, and kelps have been included on the company’s aquaculture licences.

Replanting in the wild

While developing propagation techniques, more plants have been produced than are needed for the trials. The excess Giant Kelp seedlings in particular have been made available to see if the species can be re-established in areas where it has disappeared.

In the past, Giant Kelp forests on the Tasman Peninsula rose 20 metres or more from the ocean floor. Eaglehawk Dive Centre at Eaglehawk Neck on the Tasman Peninsula once did brisk business showcasing the spectacular sight to visiting divers. But the forests have disappeared from the peninsula over the past decade, largely as a result of warm waters from the southward extension of the East Australian Current. Giant Kelp is now listed as a threatened species.

Dive centre owner Michael Baron has secured some experimental permits and replanted two sites where the kelp forests were once thick. Seeded twine obtained through the Tassal program is wrapped around bricks, which form a substrate for the growing plants.

With plantings in three consecutive years, some Giant Kelp has already reached up to six metres, offering positive signs that replanting of some areas may be possible.


National Geographic documentary

Tassal’s kelp research and the potential for broader applications feature in a new documentary produced by Stefan Andrews and Kingsley Griffin from the underwater imaging and media company Ocean Imaging.

National Geographic provided funding for the documentary, which evolved from the pair’s investigations into the disappearance of Tasmania’s Giant Kelp forests.

It was filmed at Tassal’s Okehampton Bay site, which is the centre of its integrated, multi-trophic aquaculture trials. The film will appear on National Geographic’s national website, and details how the recultivating trials are feeding back into the health of the ecosystems.


FRDC Research Code: 2017-177

More information

Craig Sanderson, 0407 522 511
craig.sanderson@tassal.com.au