Sydney Morning Herald - Emma Young
Shy dugongs, sea turtles and ancient, rocky microbes are all found among our seagrasses and mangroves. But why are politicians interested in these ocean meadows now?
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A dugong forages for food. Credit: Getty Images |
But nearby, the dugong’s nose breaks the water only to breathe, and then it sinks back down, out of sight.
The sight of dugongs and their cousins, the manatees, once led sailors to believe they had seen mermaids, hence the name of the order they belong to: sirenia. But although they are legendary, they are shy and cryptic creatures.
Despite their imposing size, they don’t emit growls or rumbles but chirp and squeak like tiny birds. They are slow to escape the paths of boats and liable to get injured. Rather than play, they prefer to lumber along the seafloor alone or in small groups in a finicky search for a favourite type of seagrass that’s made harder by the fact they have terrible eyesight. They are perhaps at their most animated when they find the grass and use their teeth to rip it out, roots and all.
It is perhaps unsurprising that such a ponderous, vulnerable animal is globally declining, threatened with extinction.
Yet their ill-suitedness to this modern world has an exception. Western Australia’s Shark Bay, on the Coral Coast stretching from Cervantes to Ningaloo, is the dugongs’ stronghold, home to the largest stable population in the world.
In this World Heritage Site, where red desert meets ocean, numerous other endangered species, and all-but-extinct scientific curiosities, find refuge. Of the world’s 50 marine World Heritage Sites, Shark Bay is one of only four that meets every natural criterion for listing.
And Shark Bay, Ningaloo and its neighbour Exmouth Gulf, along with the Great Barrier Reef, are shaping up as some of the world’s most significant hotspots for blue carbon, one of the buzzwords on which Australia’s Prime Minister has pinned hopes for a climate change response.
What is blue carbon?
It’s now common knowledge that trees store carbon that would otherwise pollute
our atmosphere.
This is why the sight of trees going up in smoke during bushfires is increasingly alarming to Australians, beyond the loss of homes and habitats the sight represents.
What is less well known is that three types of marine vegetation found where land and sea meet – seagrass beds in shallow waters, mangrove forests in between, and tidal (salt) marshes covered in saltbush – absorb and store carbon 30 times faster than forest.
As with trees, their roots and leaves store carbon, but the difference is the marine systems store most of the carbon in their soil (between 98 and 99 per cent for tidal marsh and seagrass, 60 per cent for mangroves).
And unlike with land forests, that soil is constantly building. It accumulates particles from the ocean, and sediment from run-off after storms on land.
Seagrass also provides a home for countless shell-dwellers such as clams and snails, and when these die and decompose they form carbonate sands that further build the soils.
These processes also work to furnish beaches and elevate the shoreline and seafloor, and thus not only store carbon but physically counteract sea-level rise, says Oscar Serrano, a post-doctoral research fellow at Edith Cowan University and one of Australia’s most eminent blue carbon experts.
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Eroded carbon-rich seagrass soil following a 2011 marine heatwave
in Shark Bay that killed off the grasses.
Credit: Paul Lavery |
More than half the extent of the blue carbon ecosystems were in Ningaloo, Shark Bay, and the Great Barrier Reef alone.
All three contain all three types of ecosystems. Shark Bay and Ningaloo has significant extents of all three but particularly seagrass, and Shark Bay has the world’s biggest seagrass meadow. The Great Barrier Reef has vast swaths of all types.
The report also quantifies the carbon locked away in these fields and shows they contain 40 per cent of the total blue carbon held in World Heritage marine areas.
Other blue carbon hotspots in Australia, Serrano says, are the mangrove forests of the Carpentaria and Exmouth gulfs; the seagrass meadows of Spencer and Vincent gulfs of South Australia; and the mangroves and tidal marshes of the whole tropical and subtropical region, encompassing Western Australia’s north-east, the Northern Territory and Queensland.
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Seagrass in a Shark Bay meadow, showing the deep, carbon-rich soil
beneath.
Credit: Dr Oscar Serrano |
But globally, this blue carbon is being lost faster than tropical rainforests. Damage from coastal and marine development, severe weather and the effects of climate change is causing 3 million tonnes of blue carbon to be released back to the atmosphere each year.
An extreme example was a 2011 seagrass die-off in Shark Bay caused by a marine heatwave, releasing up to 9 million tonnes of carbon dioxide and causing “black water” in the region’s famous tourist destination Monkey Mia.
Another was the 2016 dieback deaths of about 7400 hectares of mangrove forest in the Carpentaria Gulf, attributed to a combination of extreme temperatures, drought and lowered sea levels.
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Prime Minister Scott Morrison at the start of the White House
climate summit. Credit: Jessica Hromas |
In April, Prime Minister Scott Morrison called Australia’s oceans “part of the lifeblood of our economy” as he announced $100 million for ocean health including a $30 million blue carbon fund.
The promise, made as Morrison addressed 40 world leaders at US President Joe Biden’s climate summit, reflects how blue carbon is being entered into the country’s climate action political phrasebook.
As international pressure grows for Australia to set ambitious emissions reduction goals as major trading partners the European Union, UK, US and Japan have done, the federal government has resisted but is instead promoting its “practical” measures.
Green carbon is already part of the machinery of carbon offsets and credits used to counteract pollution so that Australia can reduce emissions.
The Australian government has a dedicated Emissions Reduction Fund to pay companies carbon credits to offset their pollution through planting trees.
It’s now working on an accounting method so polluters can claim credits through protecting or restoring blue carbon ecosystems.
Serrano, who is advising the government on how blue carbon projects can be banked against emissions reduction targets, says that in future any big polluter will need to invest in blue and green offsets to reach stated carbon abatement goals.
Three World Heritage sites hold 40% of the world's blue carbon
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“If you lock away carbon you want it to be locked away for centuries.”
Projects are contemplated only for tidal marsh and mangrove forest. Seagrass is harder to account for as it can’t be mapped with aerial imagery, requiring boats and human labour, which are expensive.
But Australia is one of the first countries in world to get even this far.
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A 400-hectare tree-planting project in Sukey Hill, just east of
Cranbrook in southern WA, that Greening Australia is carrying out
for Woodside, part of a 5000-hectare commitment.
Credit: Jesse Collins |
Part of the motivation could be that blue carbon may be an effective diplomatic tool for Australia, whose stance has recently been the target of angry calls for climate action from Pacific leaders; the government’s $30 million for blue carbon includes $10 million to support three restoration projects in developing countries, most likely in the Pacific.
Some Australian states are taking action of their own. Queensland is investing in blue carbon through its Land Restoration Fund, South Australia is developing a blue carbon strategy. In WA, climate action advocacy organisation Clean State has submitted to the government a $12 million blue carbon plan it says would create 270 jobs.
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A turtle on Ningaloo Reef. Credit: Getty Images |
Conserving, protecting and rehabilitating marine habitats is a worthy thing in itself, and blue carbon an interesting and legitimate scientific field, says Monash University biogeochemist Perran Cook.
Unquestionably, destruction of land and marine vegetation releases carbon dioxide and further imbalances the climate budget.
But the professor does not view blue carbon – or green – as a realistic way to combat fossil fuel emissions.
“When it’s used politically in such an important policy area, it’s hanging a hat on something very uncertain,” he says.
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Mangrove systems such as these in the Exmouth Gulf on the outskirts
of Ningaloo are easier to monitor than seagrass and so are easier
targets for blue carbon preservation and regeneration projects.
Credit: Ben Fitzpatrick |
The 20 million tonnes of carbon dioxide Australian blue carbon systems lock away each year is equivalent to less than 6 per cent of the emissions from fossil-fuel burning.
Australia’s 10 biggest polluters, all fossil fuel companies, together emit more than 150 million tonnes a year.
“The amount of CO2 we are emitting, the rate at which you’d have to rehabilitate [marine] areas would be enormous,” Professor Cook says.
The second question is, is it practical?
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And land or sea, not all offsets are created equal.
Forests might be a high-quality permanent offset in one area, such as around Cairns with its high rainfall, but not in eastern Australia where climate change might one day turn them into savanna.
And he suspects a back-of-the-envelope calculation might show Australia would “really struggle” to repurpose enough agricultural land for tree planting on the scale required.
“We have turned a lot of forest into agricultural land,” he says. “We have burned a huge amount of fossil fuels. By replanting it all … you can’t offset a lot of the burning of fuels, just the carbon released from cutting down those trees in the first place.”
The third issue is stability.
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Thousands of hectares of mangrove trees died in the Gulf of
Carpentaria in the same heatwave that caused the 2016 Great Barrier
Reef bleaching. Credit: James Cook University |
He mentions the devastation marine heatwaves caused in the Gulf of Carpentaria mangrove forests in 2016 and Shark Bay seagrass meadows in 2011.
“You’d have to be able to say it has a long term permanency to the atmosphere on a timescale of up to hundreds of thousands of years,” he says.
“The permanency of carbon in those supposed offsets is far from guaranteed.”
Serrano agrees Australia cannot rely on blue carbon alone.
“Even if we restore all blue carbon ecosystems in Australia these would only contribute a small portion of the necessary abatement,” he says. “Blue carbon needs to be part of the solution. But the solution is cutting emissions.”
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Stromatolites in Shark Bay. Credit: Getty Images |
Dugongs are not the only unique life forms along the Coral Coast that climate change places at risk. Numerous other endangered species rely on seagrass, such as green turtles. Dependent on the turtles are the tiger sharks that give Shark Bay its name.
Also in Shark Bay is the world’s only significant assembly of live stromatolites – reefs of rock and microbe domes, once the planet’s dominant life form, before the creation of oxygen rendered them extinct virtually everywhere but this sheltered, shallow and hyper-saline site.
NASA has studied them as part of a search for life on other planets, and like the water surface that hides the 10,000 dugongs cruising beneath, the single tourist boardwalk gives little perspective on the stromatolite reefs’ 135-kilometre expanse, on which only the odd researcher is permitted.
In Shark Bay another anachronism survives: a tiny cultivated pod of dolphins visiting the beach reliably and daily to interact with humans, achieving world fame among tourists and scientists.
At the other end of the Coral Coast, 400 kilometres north, Exmouth Gulf beside Ningaloo Reef is the only known site worldwide where green sawfish give birth to pups. A five-metre-long shark-like creature whose toothed snout, as long as its body, resembles a chainsaw blade, it looks fearsome but is one of the planet’s most endangered species.
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A green sawfish. Credit: Getty Images |
The peninsula on which Exmouth sits has fossilised coral reefs that date back to the last Ice Age, and whose very form has contributed to this staggering biodiversity by sheltering the Gulf from the rest of the ocean for millennia.
And this is just what is already known. The only region-wide survey of Exmouth Gulf in recent years found science had barely scratched the surface when it comes to the multitude of species living there, but it also found that despite this the Gulf would probably already qualify for World Heritage status.
Sea-level rise, marine heatwaves and cyclones threaten all the curiosities found in these blue carbon hotspots and those across Australia.
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‘Black water’: The three Australian sites that are ground zero
for climate change |
These dugongs form vast herds to raze their preferred seagrass variety annually, encouraging regular new, tender and delicious growth. The process is so uncannily like farming that experts call it “cultivation” grazing. Yet the dugongs cause no harm.
Unless we too can find a positive way to work with nature, the interconnectedness of all these systems suggests humanity stands to lose more than just safety and comfort to climate change; we stand to lose wonder, too.
Saving and preserving blue carbon ecosystems might not be the complete answer. But it could be a start.
With thanks to Dr Amanda Hodgson, aquatic megafauna research fellow at Murdoch University, for her insights into the life of a dugong.
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