Sea urchin alert: clear and present danger

Back in 2004, Scott Ling used his meagre student allowance to print off a brochure about long-spined sea urchins and took one of the sea creatures in a small tank to Tasmania’s Agfest.

“No one knew what this thing was,” Ling, who is now an Associate Professor with the Institute for Marine and Antarctic Studies (IMAS), told a Senate committee inquiry.

Now, close to 20 years later, more than 20 million of the sea urchins – Centrostephanus rodgersii, or “Centro,” are troubling the east coast of Tasmania, wreaking havoc on reefs and kelp forests, and threatening the seafood industry.

In September last year, the Senate referred an inquiry into the spread of climate-related marine invasive species – particularly long-spined sea urchins – to the Environment and Communications References Committee, with a report due in March 2023, now extended until July 31, 2023.

The Centro – something like a small black ball covered in spines – is a native resident of the waters of New South Wales and Victoria, but climate change has led to a southern range-extension and population explosion, with particular concern in Tasmania, where it has invaded the reefs.

More than 130 representatives from the fisheries industry, government, research, Aboriginal communities, recreational fishing groups and community groups met at the 2023 National Centrostephanus Workshop in Tasmania earlier this year.

It heard that it is estimated there are now over 20 million long-spined sea urchins in Tasmania waters alone, impacting over 1,500 kilometres of south-east Australian coastline.

Also in Cosmos: never mind the sea urchin the whole 8000km southern reef is in peril

Dr Ling has recently revisited the “epicentre of sea urchin overgrazing,” St Helens in the north-east of Tasmania. St Helens is part of 156 Tasmanian sites that have been surveyed for long-spined sea urchins with 108 sites surveyed in 2020-21.

“By all reports there were very few long-spined urchins in the 1970s,” Ling said. “Our surveys in 2001-02 and then 2016-2017 showed clear changes in terms of the sea urchins almost doubling in abundance and quadrupling in terms of overgrazing.

“We started to see this through very clear data across the 156 sites.”

Climbing ocean temperatures between the mid-1990s and early 2000s had also led to the appearance of warm water species such as yellowfin tuna in areas never seen before.

Ling says IMAS scientists put out an alert of “clear and present danger,” warning the sea urchin population explosion was likely to lead to a potential halving of productive kelp bed habitats which provide a home for the Tasmanian rock lobsters and abalone.

“It’s like most disaster movies. It starts with a scientist being ignored,” says Ling.

But the ever-increasing over-grazed reef areas known as “barrens” had begun to attract attention and the problem was being witnessed firsthand by abalone divers.

Among the management control methods has been the harvesting of sea urchin roe which has found an international market. Commercial fishing of the sea urchins was subsidised initially by the abalone industry, then the Tasmanian Government, at a cost of 75c a kilogram between 2016 and 2019.

The subsidy structure was altered after 2019 to reflect different regions of the coast and target new areas of incursion by the urchins.

Diver with small recovery on kelp barren border 1230019 1 2
Diving over a barren caused by overgrazing by long-spined sea urchins. At left is a healthy kelp bed. Image by Matt Testoni. 

“As the saying goes, an ounce of prevention is worth a tonne of cure,” Ling says. “We have to triage the problem and put all our efforts into those areas we can save.

“It’s a bit like fighting wildfire. You can put out the spot fires, but once the fire front has really built up momentum it’s very hard to halt.”

Other experiments have concentrated on completely removing the population of long-spined sea urchins in a particular area.

“We see the fishery industry as a key part of the solution,” Ling says.

The latest survey of St Helens has shown that among the barrens are some areas of recovery of the kelp habitat. A 2019 evaluation of the sea urchin harvest subsidy found more than 1100 tonnes of long-spined urchins had been removed over 10 years. A further 1900 tonnes has been removed since.

But the problem remains.

The Tasmanian State Government submission to the Senate enquiry, supported by the likes of the Great Southern Reef Foundation, called for development and implementation of a $50 million regional long-spined sea urchin management plan.

“Management for long-spined sea urchins is a complex challenge, with over 2000km of south-eastern Australia affected,” the submission stated. “There is no simple, one-size-fits all solution.”

Ling says a management plan is important.

“The population in New South Wales is reaching us in Tasmania and there is only so much you can do if the flow continues. I use the analogy that if a bathtub is overflowing, the first thing you have got to do is turn off the tap. But through time we are likely getting more and more self-recruitment within Tasmanian waters.”

The key, Ling says, is further research and an integrated approach that looks at the balance of the whole reef ecosystem, including the regeneration of kelp forests, and managed harvesting of long-spined sea urchins.

“This is the holy grail – an ecosystem-based way of managing this threat. It could be an exemplar for elsewhere.”

The Greenlight Project is a year-long look at how regional Australia is preparing for and adapting to climate change.

The Ultramarine project – focussing on research and innovation in our marine environments – is supported by Minderoo Foundation.

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