THE UNSUNG REEF

Australia’s corals may get all the headlines, but its kelp-dominated temperate reefs are as important and imperilled. Now they’re finally getting the restoration focus they deserve.

Reefs don’t need coral to be enchanting and ecologically important. STEPHANIE STONE reports on efforts to restore kelp-dominated wonders off the coast of Tasmania.

ASTHICK SHEETS OF cold 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. Stemlike 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 by marine 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.” > page 55

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Photography Justin Gilligan Bull kelp washed up on the coast of Tasmania

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.

Weedy seadragons (middle; Phyllopteryx taeniolatus) are similarly poor swimmers. This male in Tasman Peninsula waters carries eggs on the underside of its abdomen – it’s one of few species whose males care for eggs. The loss of kelp forests is a major threat to these delicate reef fish.

Unlike most anemones, southern swimming anemones (top; Phlyctenanthus australis), like this one in waters off Maria Island, Tasmania, are mobile. They’re able to release their grip on a perch and swim, albeit clumsily, to a new patch of kelp in the surrounding forest.

Spotted handfish (bottom; Brachionichthys hirsutus) are bottom-dwellers in the Derwent River Estuary, near Hobart. The handfish’s speedy decline in range and abundance led to it being the first marine fish listed as endangered under the Federal Environment Protection and Biodiversity Protection Act 1999. Forests of giant kelp (Macrocystis pyrifera) are missing from more than 95% of the species’ historic range. Among those enduring (opposite) were communities near the Actaeon Islands in southern Tasmania, but recent reports suggest that these too may have disappeared.