The hypnotic sway of kelp fronds as they dance with the surge of the ocean was once a common site along the Great Southern Reef.
In recent times, these important ecosystems have been under threat. They support a high diversity of marine life, abalone and crayfish fisheries, coastal tourism and recreational industries. These ecosystems also help to remove excess nutrients in the water and sequester carbon from the atmosphere.
The declining kelp forests in Port Phillip Bay
The kelp forests and macroalgae habitat in Port Phillip Bay have undergone significant decline in the last two decades, mostly because of the increase in the numbers of Purple Urchin (Heliocidaris erythrogramma) and changes in water quality.
This has led to these important habitats being replaced by ‘urchin barrens', which appear as areas of bare reef devoid of much marine life and up to 60 urchins per m2.
Urchin barrens have replaced important reef habitat across an estimated ~13 km2 of reef within Port Phillip Bay, with approximately 60% of all rocky reefs (by area) in Port Phillip Bay impacted by overgrazing of urchins[1] .
[1]Johnson, C. R et al. 2015. The reef ecosystem evaluation framework: managing for resilience in temperate environments. Seagrass and reefs. Final report for Department of Environment, Land, Water and Planning, Victoria, Australia
The Port Phillip Bay Golden Kelp Restoration Project
With funding from the Victorian Government’s Department of Energy, Environment and Climate Action, the Port Phillip Bay Golden Kelp Restoration Project commenced in 2022 to research and develop scalable solutions to reocover these important ecosystems, building on over 10 years of research into kelp and urchin dynamics in Port Phillip.
The project was a partnership between The Nature Conservancy, The University of Melbourne, Deakin University and Parks Victoria and brought together Victoria’s leading organisations working with kelp and urchin research, management and restoration.
While urchins are an important part of a healthy kelp forest, without intervention further loss of kelp forests and macroalgae habitat in the bay would continue. The important first step was reovery and thefore to reduce urchin abundances to healthy levels (~2 urchins/m2).
Over the two-year project, in situ culling of urchins was conducted across 9 hecatres of urchin barrens in Jawbone Marine Sanctuary in Williamstown and Ricketts Point Marine Sanctuary in Beaumaris.
By targeting these urchin barrens, culling efforts have protected an additional 15 hectares of existing macroalgae and kelp forest habitat.
Researchers from Deakin Queenscliff Marine Science Centre developed successful techniques to cultivate golden kelp from the microscopic life stage on twine and gravel, which were then outplanted into urchin barrens.
Over the two-year project, TNC outplanted approximately 400,000 juvenile kelp, grown on 3km of cotton twine, and 500 kg of seeded green gravel, and also transplanted 400 mature kelp from healthy populations, to help recover these ecosystems.
The University of Melbourne are undertaking a robust monitoring program which will continue over the coming years to assess the outcomes and to inform future management options.
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Bringing the kelp forests to life
To date, monitoring is showing that all restoration methods are working well, with outplanted kelp successfully attaching to the reef and maturing, and even starting to become reproductive. After just 7 months, the outplanted kelp were already on average 20 cm tall, and they’re even bigger now!
The natural recovery in areas where urchin numbers have been reduced to healthy levels has also been very encouraging, with many native seaweed species returning to these areas. Unsurprisingly, monitoring has also confirmed that in areas where urchin numbers haven’t been reduced, golden kelp and macroalgae are not recovering.
Reviving the sea floor
Transplanted kelp forests reviving the seafloor Port Phillip Bay - ABC News
The help for kelp continues
In 2024, The Nature Conservancy, Parks Victoria and the University of Melbourne were awarded a grant through the Port Phillip Bay Fund to continue urchin management and kelp restoration efforts in the bay.
Over the next three years the team will reduce urchin numbers in a further 5 hectares of urchin barrens and continue to outplant hundreds of thousands of juvenile kelp. As part of the project The Nature Conservancy is working with the aquaculture industry to build capacity to cultivate kelp, and help take restoration to the next scale.
Lookout for further updates as this work progresses.