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
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At Australia’s westernmost point lies the Coral Coast, a land of strange
extremities. Marine megafauna is more accessible than ever before. Tourists swim
with humpbacks and manta rays and whale sharks. They hand-feed playful dolphins
that obligingly stick out scarred and blemished dorsal fins scientists can use
to identify them as individuals, name them and track their social behaviours.
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
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Serrano was one of the lead authors of a report published in 2021 by UNESCO,
which for the first time assessed the vegetation fields in its 50 marine World
Heritage Sites. Significant hotspots included America’s Everglades National Park
in Florida, the West Norwegian fjords and France’s lagoons of New Caledonia, but
none were as impressive or diverse as Australia’s.
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
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Together, Australian blue carbon ecosystems sequester 20 million tonnes of
carbon dioxide a year. That’s like taking 4 million cars off the road.
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
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An environmental solution or a political one?
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
He says the capacity of blue carbon per square metre is vastly greater than
green. “Soils underneath the forest also have carbon but once the forest is
mature the soil can’t accumulate more,” he says. “Most of the carbon is in ...
the trees themselves. And they don’t live forever. They live 50, 100 years.
“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
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“My feeling is the Australian government is wanting to take the lead worldwide
on this, and they are starting with this, but soon other methods will follow and
hopefully they will include seagrass,” Serrano says.
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
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Can blue carbon help us meet emissions reduction targets?
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
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The first question is, can blue carbon restoration and protection balance our
carbon budget?
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?
Cook says that as with any marine engineering, restoration of blue carbon
ecosystems is relatively expensive.
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
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Cook questions the idea of blue carbon having a longer lifespan in times when
climate change, marine heatwaves and rising sea levels are destabilising oceans.
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
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What else is at stake?
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
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Unseen along this stretch of coast are “stygofauna” found nowhere else but WA,
the blind cave eel and blind gudgeon fish living deep underground in a complex
terrain of limestone caves, rivers and lakes.
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.
Meanwhile, happily oblivious in Moreton Bay, Queensland, one of Australia’s
smaller populations of dugongs is even more idiosyncratic than its western
counterparts.
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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