Shark Bay, in Western Australia, attracts tourists for its stunning scenery. Here, red rocks meet white sands meet blue waves. Perhaps the region’s greatest asset, though, is hidden beneath the waves: one of the world’s largest seagrass meadows.
Spread across more than 180km2 (69 miles2) of seabed, this underwater forest is home to sea cucumbers, snapper fish, the endangered dugong sea cow and more.
A little further south lies the 8,000km-long (almost 5,000-mile) Great Southern Reef, which provides a home for another submerged forest. Tall swathes of brownish seaweeds, known as golden kelp, grow from the coral. As in terrestrial forests, the canopy provides cover for a host of smaller species living below.
Such marine forests form gigantic stores of ‘blue carbon’, but they’re threatened by rising sea temperatures fuelled by climate change, pollution, dredging and other human-inflicted harms.
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During the summer of 2010-2011, for example, Shark Bay, and Western Australia more widely, suffered devastating losses of seagrasses and corals as sea surface temperatures soared to more than 3°C above average.
“Since then, we’ve been monitoring how that loss has changed and, although [the seagrasses] have recovered, over the regions there does seem to be a downward trend,” says Nicole Said, a seagrass scientist at Edith Cowan University in Joondalup near Perth.
The fight isn’t over yet, however. Across Australia, attempts to rejuvenate underwater forests are galvanising communities.
At Shark Bay, a collaboration involving scientists from the University of Western Australia and local organisations, including those representing Aboriginal interests, has been working to replant the lost seagrasses. Last year, they transferred 5,000 new cuttings, while checking up on how transplants from the previous year had fared (around 70-80 per cent had taken to their new surroundings).
Meanwhile, nearly 3,800km (approx 2,360 miles) away on the opposite coast, new government funding for the Coastal Marine Ecosystems Research Centre (CMERC) in Queensland promises to improve the centre’s nursery facilities for seagrasses.
Growing knowledge
Based at CMERC, Markeeta Sullivan, who is Yidinji by background, is one of over 200 Indigenous Land and Sea Rangers to receive training through partnerships between the Queensland government and First Nations organisations. She gave up working as a chef to join CMERC scientists studying and looking after Queensland’s seagrass and mangrove forests.
Together with the Great Barrier Reef, these forests act as natural fortifications against rising seas and erosion.
As she explains, there’s an important cultural significance for Indigenous people in this work, which is known as ‘taking care of country.’ “We’re trying to bring the wildlife, or the marine life, back to its natural state – the way it was before the ‘human footprint’,” she says.
“We try and go, culturally, by what has been taught, but a lot of people have lost that traditional knowledge.” While elders and Indigenous people on the coast know about the dugongs and green turtles that live in the seagrass meadows, awareness of the seagrasses themselves is lacking.
Collaborating with scientists, Sullivan says, can be a way to regain and build on traditional knowledge.
The nursery at CMERC currently houses nine saltwater tanks filled with seagrasses in flowerpots. Sullivan keeps a careful watch on them, using paper towels and mesh to stop the plants’ sediments from leaking out, and replacing it when it does.
Experience tells the team these seagrasses would have only a slim chance of surviving if they were reintroduced to the meadow. Tidal changes mean that their wild counterparts absorb more sunlight (driving photosynthesis) at certain times of the day, whereas in the tanks, the plants grow fragile from sitting below water 24/7.
New funding will allow for computerised systems that automatically produce changes in water depth, to mimic tides and create the right conditions for flowering, so that she can collect seagrass seeds.
Volunteer organisations such as OzFish, which aims to restore fish habitats across Australia, also collect seagrass seeds to resew thinning seagrass meadows. At OzFish’s ‘Seeds for Snapper’ project in Cockburn Sound, just off the southwest coast near Perth, volunteer divers help by picking the ripe, green fruits that contain the seeds straight from the plants.
The seeds are released into water tanks, then thrown into the sea from a boat at a seeding location, where they’ll sink to the seabed and, hopefully, germinate.
As Program Manager for OzFish in Western Australia, Steve Pursell, says, “With the way that Posidonia australis [a species of seagrass] produces its fruit, about 90 per cent of what’s released can’t grow because it either washes up on the beach or gets taken out to deep water. So we’re stepping in and helping nature.”
In the last two years, OzFish volunteers at Cockburn Sound have put around two million seeds back into the water. The region’s seagrasses provide important habitats for baby pink snapper fish, but have been degraded by pollution and the heatwaves that affected Shark Bay’s seagrass meadows further up the coast.
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Increasing resilience
Scientists are researching other ways to make underwater forests more resilient. Said’s research involves figuring out how well different seagrass populations along the west coast are able to withstand heat – by measuring their photosynthetic rate at different temperatures.
Assuming the more northerly seagrass meadows can tolerate higher temperatures, one approach could be to transplant some of these heat-resistant plants, or their seeds, to meadows further south. “It’s not like changing genetics, although you are introducing a new plant that may have different genetics to that meadow,” she says. “But the point would be to make them stronger in the face of climate change.”
While it could be simple to scale up such an effort by joining forces with programmes like Seeds for Snapper, to relocate seagrass seeds, Said hints at some ethical considerations that need to be addressed; specifically the accusations of ‘playing God’ that have been levelled at scientists trying to save Australia’s corals.
Given the grim reality that reefs are facing – by some estimates, corals along the Great Barrier Reef have been depleted by half in the past 30 years – it’s little wonder that scientists are having to think outside the box.
At the Australian Institute of Marine Science (AIMS), Dr Annika Lamb is aiming to bolster coral’s resistance to increasing temperatures through breeding.
As she is careful to point out, this is just part of what should be a multi-pronged conservation approach, with other key aspects including tackling carbon emissions and protecting reefs through management of fisheries and water quality. “In light of these other management strategies taking time, we’re trying to buy time by intervening through this process of reef restoration,” Lamb says.
Her team’s strategy takes advantage of corals’ predictable natural cycles to carry out something akin to IVF. Corals are animals, so they produce eggs and sperm like humans – except, as they’re stationary, corals release their ‘gametes’ (reproductive cells) into the sea where, ideally, some of them will meet to produce coral babies.
In nature, this spawning event, which Lamb likens to ‘reverse snowing’, happens a few days after a full Moon. Now, though, the team at AIMS can cue spawning in the lab through clever use of lighting and temperature settings. This allows the researchers to collect and mix gametes from corals of the same species that wouldn’t normally breed together because they live in different locations.
Testing the offspring of these unlikely parents is allowing the researchers to identify combinations that produce corals capable of thriving in warmer waters.
Other researchers at AIMS are focusing on tiny symbiotic algae that live inside corals’ tissues. It’s the loss of these algae, which photosynthesise to provide nutrients needed by coral, that turns coral white and makes them vulnerable when bleaching occurs due to heatwaves.
What Dr Matthew Nitschke and Prof Madeleine van Oppen are now showing is that they can produce ‘heat-evolved’ versions of the algae by forcing them to adapt to hotter conditions within lab cultures. They’re now testing whether corals that play host to heat-evolved algae are also more resilient and are in the early stages of a small field trial.
Escalating threats
While the plight of corals, and to some extent seagrasses, is well-known, the dire situation of kelp forests – whose reserves of carbon remain largely unquantified – is less well-publicised. The last 50 years have seen around half of the world’s kelp forests fall into decline.
As kelp scientist Dr Georgina Wood, based at Flinders University and the University of Western Australia, explains, kelp forests in Australia are being compressed by temperature extremes in the north. So much so, that within 100 years all that will be left is a thin band around the south coast.
On the east coast, efforts to restore seaweed forests have seen a success, and issues of poor water quality have been fixed. “But increasingly we’re seeing that seaweeds are getting stressed because of ocean warming – longer-term threats that we’re not going to be able to get around,” says Wood.
This is why scientists are turning to ‘assisted migration’ strategies similar to those being considered for seagrasses, which will bring heat-tolerant seaweeds further south. Replanting is tricky, since the seaweeds need to attach to the coral, so Wood’s team and others work with a material called ‘green gravel’, which gives young seaweeds a surface to attach to in the lab before being scattered over the reef.
While Australia’s underwater forests are dwindling, the enormous energies being expended to maintain and restore them show the determination of the Australian people to protect their natural environment for the future.
The biggest challenge, warns Michael Wear, a Malgana ‘traditional owner’ whose company, Tidal Moon, was involved in last year’s seagrass restoration project at Shark Bay, is not replanting the forests, but avoiding doing more harm than good in the process. He wants to ensure restoration attempts don’t unbalance nature by focusing too hard on, say, seagrasses and disregarding the rest of the ecosystem.
For Indigenous people, it’s about considering biodiversity more broadly, hence it’s important to include a variety of perspectives and knowledge. “Scientists normally look at one thing that they study, like a seagrass, [whereas] Indigenous people, they like to look at the whole environment,” he says.
It’s a reminder that restoration efforts can’t be left to scientists alone, not only because there’s too much to do, but because others have valuable insights to share. Time will tell whether Australia gets it right.
Why are seagrasses so vital to life?
Tropical rainforests are known as the ‘Earth’s lungs’ – they ‘breathe in’ the carbon dioxide that’s warming our atmosphere to use for photosynthesis and lock it away. Seagrass meadows do the equivalent, but in the ocean.
As well as absorbing carbon dioxide from sea water, they sequester carbon in floating particles and the remains of dead sea creatures that get stuck in the sediments supporting their roots. Once trapped, this carbon can stay there for centuries, assuming the seabed is undisturbed.
Scientists estimate that the world’s seagrasses may take up as many as 44 billion kg of carbon each year, although that number will decrease if they continue to be lost.
Seagrasses also play a key role in protecting coastal areas from erosion, by stabilising the sediment and pushing up the height of the sand so that it acts as a natural barrier.
They’re also important habitats for marine life, providing nurseries for young animals and shelter from predators. Some larger sea creatures, like turtles, manatees and dugongs eat the leaves, while others, such as dolphins, feed on the smaller animals that live among them.
About our experts
Nicole Said is a seagrass scientist at Edith Cowan University in Joondalup near Perth, Australia. Her work has been published in Western Australian Marine Science Institution, Earth System Science Data, and Elsevier Estuarine, Coastal and Shelf Science.
Markeeta Sullivan is a key figure in the CMERC seagrass nursery and one of over 200 Indigenous Land and Sea Rangers to receive training through partnerships between the Queensland government and First Nations organisations.
Steve Pursell is the Program Manager for OzFish Western Australia.
Dr Annika Lamb is a leading researcher for the Australian Institute of Marine Science and is working for the team under the Australian Government for The Reef Restoration and Adaptation Program on the 'Breeding temperature tolerant corals for reef restoration and adaptation' research project. Her work has been published by The Genetics Society, Wiley Evolutionary Applications, and Frontiers in Genetics.
Dr Georgina Wood is a marine ecology and genomics expert based at Flinders University and the University of Western Australia. Her work has been published in Molecular Ecology, Journal of Phycology, and Global Change Biology.
Michael Wear is a Malgana ‘traditional owner’ and the managing director of Tidal Moon.
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