Tasmania’s giant kelp has all but vanished, but worldwide restoration efforts provide hope the precious habitats can be rejuvenated
The thick underwater forests off Tasmania’s east coast used to be so dense they were marked as shipping hazards on nautical charts. Thriving stands of giant kelp, which grows up to 40 metres high, once provided habitat for fur seals, seahorses, weedy sea dragons, rock lobsters, abalone and fish.
Since the 1960s, Tasmania’s giant kelp has all but vanished. Despite the rapid speed at which the brown algae grows – up to half a metre a day – around 95% has been killed off by warm waters pushed southwards by the east Australian current.
“Coral reefs and the Great Barrier Reef get a lot of attention, and a lot of funding,” says Dr Cayne Layton, of the University of Tasmania’s Institute of Marine and Antarctic Studies. “Kelp forests and many other temperate, or cold water, marine ecosystems really suffer from an ‘out of sight, out of mind’ kind of mentality.”
In addition to supporting complex ecosystems, kelp has “a really important job in maintaining water quality in coastal areas”, he says. For the last two years, Layton and his colleagues at IMAS have been working on restoration projects at several sites off the Tasmanian coast.
The team has grown and planted giant kelp that is naturally more tolerant of warm water – up to 4C more heat-resistant than average.
“Tasmania is not only getting warmer, our coastal waters are also declining in nutrients. It’s hard to unpick exactly which of those factors is more important,” Layton says. He hopes the heat-tolerant plantings could be more resilient to low nutrients.
Kelp restoration has lagged behind efforts to protect other marine ecosystems, which Layton attributes to a funding shortfall, but also the physical challenges of working in relatively deep, rough and rocky environments.
But restoration efforts around the world are increasing in frequency, according to a recent analysis of kelp projects spanning 1957 to 2020. The study, published in Biological Reviews, analysed 259 restoration attempts across 16 countries in an effort to comprehensively document successful approaches.
Most kelp restoration projects took place on a scale of less than a hectare, the review found, but large-scale restoration was possible: six recorded projects successfully restored more than 100 hectares of underwater forest.
Culturally and economically significant
In addition to their ecological benefits, kelp forests are also economically and culturally significant, says Aaron Eger, the review’s first author and a PhD student at the University of New South Wales. Protecting these ecosystems, he believes, is vital for preserving social connections that date back “hundreds if not thousands of years”.
Kelp is estimated to generate $100,000 USD a hectare a year, amounting to billions of dollars annually. It is harvested and refined to yield alginates, compounds used widely as a thickener in foods and cosmetic products. Edible kelps are widely consumed in east Asia – known as kombu in Japanese, dasima in Korean, and haidai in Chinese.
The first recorded restoration project dates back to 1718, when a Japanese monk instructed fishers to throw stones into barren areas to encourage kelp regrowth. To thrive, kelp requires a hard substrate such as rock or sand, water rich in nutrients such as nitrogen and phosphorus, and light.
The most successful projects in recent decades have operated on timelines sufficiently long – between 10 and 20 years – to make a difference at scale.
“Japan and [South] Korea have invested heavily in restoration,” Eger says, adding that significant government investment is still the exception, rather than the rule.
“There’s been more success overall than we thought we might find,” says Prof Adriana Vergés, a marine ecologist also at UNSW. Their review found that the effective method was to transplant kelp from a donor site. In addition, the biggest predictor of a project’s success was proximity to a nearby kelp forest.
“What that tells us is that the number one priority should be to protect what we still have,” Vergés says.
As part of their research, Eger and Vergés visited some restoration projects in South Korea. At one site, it was barely conceivable that just four to five years earlier the place had been barren. “It was covered in kelp, filled with abalone, crabs, octopus, fish,” Eger says. “It was inspiring to see.”
The approach in Japan and Korea is “much more interventionist” than in Australia, Vergés says, and uses techniques such as creating artificial reefs to restore kelp at large scales.
“In Australia we have much more of a hands off philosophy when it comes to managing our marine environment,” Eger agrees. “We incidentally cause the damage but … we think nature should come back on its own.”
Thorny problem
The biggest barrier to success – and also the most common factor that necessitates kelp restoration in the first place – is the incursion of sea urchins, the review found.
Restoration projects in Australia – as well as Norway, Japan, Korea and California – have been hampered by urchins, while marine heat waves have killed transplants in Australia, Chile, and California.
“In California they’ve lost 90% of their kelp forest because of urchin overgrazing,” Vergés says. “Wherever there’s either overfishing or a heatwave-mediated decline of their predators, the sea urchin numbers go up through the roof and they mow down the entire kelp forest.”
One potential solution may be to eat the urchins. In Tasmania, hundreds of tonnes of long-spined sea urchins are now commercially harvested each year for their gonads, which are edible. “They’re turning this pest into a profitable commodity,” Layton says.
The challenge, however, is that natural kelp recovery effectively requires the removal of every urchin from a given area. “But the way the fishery works is the fishers will take 70 to 75% and then it’s more economical for them to move to a new area,” Layton says.
“We’re starting to look at different ways where we can partner with the fishers,” he says. “Maybe you can subsidise them to spend a bit more time there and remove every single urchin.”
The speed at which kelp grows – up to eight metres a year, depending on the species – makes restoration heartening, Eger says. “You can see kelp forests return in a single year.”
“Drastically reducing our [carbon] emissions is still priority number one,” Layton says. “But the hope is that we can intervene in the meantime and buy some time for these really critically important ecosystems.”
Source: The Guardian
