50 – COSMOS Issue 86
SUSTAINABILITY BIOLOGY
AS THICK SHEETS OFcold mist crept
over the docks in Tasmania’s Pirates Bay hours before
the sunrise, Simon Wally and Shane Bloomfield
donned raingear still damp from the days before and
loaded well-used gear onto the boat. The sky and water
were both still inky when they cast off to check the
lobster traps they’d dropped the previous afternoon.
When the men pulled up their traps, they found
southern rock lobsters (Jasus edwardsii) inside,
although fewer and smaller than they used to expect.
The pots also held a few eastern rock lobsters
(Sagmariasus verreauxi), a warm-water species that
never used to venture into southern Tasmania. Their
haul was a snapshot of a changing fishery.
The Great Southern Reef, a 71,000 square
kilometre band of kelp-dominated coastline that
stretches from Brisbane around Tasmania to Kalbarri,
brings in more than $7 billion annually in fishing and
tourism dollars alone. Yet the reef wasn’t named until
a multi-disciplinary team of scientists published a
paper in 2016 arguing for its recognition.
The Reef ’s relative obscurity could be due to the
understated qualities of the organisms that define
it: kelp and other seaweeds. These are macroalgae,
lumped into the same hodge-podge taxonomic group
as amoebas and slime moulds – but comparisons to
plants are inevitable.
They photosynthesise; they have leaf-like structures,
called blades, that capture sunlight and convert it to
storable carbohydrates; they have root-like structures,
called holdfasts, that anchor them to the bottom. Stem-
like structures, called stipes, carry their blades toward the
sun – growing, in the case of giant kelp, at an astonishing
rate of 50 centimetres per day. Like a rainforest’s trees,
seaweeds are the foundation of their world.
“They support entire ecological communities,”
explains Adriana Vergés, a marine ecologist at the
University of New South Wales. “Hundreds of species
that get shelter, food, and habitat from these seaweeds.”
Kelp requires cool, nutrient-rich waters to thrive.
Long-term exposure to higher temperatures weakens
kelp, slows its growth rate, and impedes its ability to
reproduce. In addition to these direct impacts, ocean
warming allows new herbivores, including tropical
fish and urchins, to move into kelp forest terrain.
In Tasmania, ocean warming is occurring about
four times faster than the global average. Giant kelp
(Macrocystis pyrifera) has been hit the hardest; over
the past 75 years, the species has disappeared from
95% of its former range.
This dramatic decline was first documented bymarine ecologist Craig Johnson from the University of
Tasmania (UTAS), who compared aerial photographs
taken from the 1940s through 2011 to track the species’
shrinking range. Now, he says, this “iconic and very
important coastal marine community is essentially
gone from much of the east coast of Tasmania”.
In 2015, Johnson and a group of UTAS colleagues
transplanted healthy common kelp (Ecklonia radiata)
onto more than a hectare of barren seafloor off the
eastern Tasmanian mainland.
Within six weeks, the team’s patches were
crammed with a wide range of animals and other
algae species. For the next 18 months, they studied
the growth and reproduction success of the kelp.
“One of the primary things we learned is that
there is a critical minimum patch size and density that
must exist for kelp patches to be self-sustaining,” says
Cayne Layton, a postdoctoral researcher who works
with Johnson. “Juvenile kelp struggle to survive
where there is insufficient adult kelp.”In rough seas off Tasmania’s
Tasman Peninsula (top),
crayfisherman Shane
Bloomfield (opposite above)
tosses a southern rock lobster
into a container on the deck
of his cray boat. Cray catches
are being affected by warming
waters and the decline of
kelp forests. King Island kelp
harvester John (opposite
below) stacks up a trailer
load of bull kelp (Durvillaea
potatorum), with vigilant
kelpie Bruce on watch. The
kelp yields alginates that are
used to produce gels and
pastes, pharmaceuticals,
shampoos, and more.
> page 55