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There are zombies lurking at the bottom of Port Phillip Bay. But before you picture a 28 Years Later-style quarantine zone, though, these are far from bloodthirsty, human-hunting undead.
Instead, we’re talking about small, native sea creatures capable of taking over an ecosystem before settling into an indefinite ‘zombie’ state. Meet the short-spined purple sea urchin.
Horror movie comparisons aside, this prickly creature plays a vital role in the Port Phillip Bay ecosystem. Right now, though, that ecosystem is in trouble.
Urchin numbers have surged, upsetting the natural balance and threatening other species. Graduate researcher Rick Verkooijen is working to tackle this short-spined purple sea urchin problem. We sat down with Verkooijen to explore the bay’s purple sea urchin problem, why urchin numbers have spiralled and his surprisingly delicious solution.
So what exactly are sea urchins? These round, spiky creatures are commonly found on rocky reefs all over the planet – ‘from the poles to the tropics and down to depths of 7000 meters,’ according to Verkooijen. If you’ve ever felt the spiky sting of stepping on an urchin, you might question their purpose, but Verkooijen says that sea urchins play a vital role in underwater ecosystems.
‘Urchins are primarily herbivores and love to eat a variety of seaweeds,’ Verkooijen says. ‘When populations are in balance, they fulfil an important role as herbivores, controlling the growth of macroalgae and other marine plants.’
One of the most common urchin species in Australia is the short-spined purple sea urchin – also known by its scientific name, Heliocidaris erythrogramma. Despite its name, this species can range from red or violet to green and white. As Verkooijen explains, these spiky natives are both abundant and important.
‘The short-spined purple sea urchin is endemic to the Great Southern Reef and lives all the way from the subtropics to Tasmania and across to Western Australia,’ he says. ‘It is a native species and has both ecological importance as an herbivore and economic importance as a targeted species for fisheries.’
If these prickly critters are so valuable to our undersea ecosystems, then why all the talk of a short-spined purple sea urchin problem in Port Phillip Bay? As Verkooijen explains, these sea urchins aren’t bad for the environment – that is, unless their numbers get out of hand.
‘Urchin populations have exploded over the past decades as a result of drought, nutrient imbalances in the bay, a loss of predators and climate change,’ he says. ‘Where they first played an important role in the bay as drift-feeders – feeding on algae that were detached and acting basically as a cleaner of algal waste – they shifted to eating golden kelp that was attached to the reef during the millennium drought.’
Golden kelp is a key part of ecosystems in Port Phillip Bay and beyond. But, with short-spined purple sea urchins increasingly feeding on kelp forests, that vital ecosystem is in trouble.
‘As urchin numbers increased they stripped away about 70% of kelp forests in Port Philip Bay,’ says Verkooijen. ‘After stripping the reefs the urchins don’t leave, they enter a “zombie” state which they can stay in for many decades, continuously grazing away any regrowth that might occur. The urchins basically leave behind an urchin dominated desert that we like to call an urchin barren.’
In their natural habitat, short-spined purple sea urchins are important drift-feeders and algal waste cleaners. Up here on land, though, these urchins are better known for something else entirely – the culinary value of, as Verkooijen puts it, their ‘valuable gonads’. In other words, people love to eat purple sea urchin roe, a delicacy that becomes plentiful and delicious when urchins have access to a rich diet.
‘Urchin roe is a highly sought after seafood product in countries like Japan,’ Verkooijen says. ‘The purple urchin in particular can be highly valuable, around $1000 Australian dollars per kilogram.’
Known as ‘uni’ in Japan, the roe is described as having a delicate texture and sweet, creamy flavour.
So, urchin roe is delicious – but how does that help with Port Phillip Bay’s short-spined purple sea urchin problem? Verkooijen believes it’s part of a potential solution.
As it stands, the urchins living in the ‘barrens’ of Port Phillip Bay are of little culinary value, lacking the roe that makes them so prized on the dinner table. As Verkooijen explains, the issue is that urchins can only produce a bounty of roe when their diet is rich enough. As it stands, the imbalance in their natural habitat means Port Phillip Bay urchins don’t have access to a sufficient diet for roe production. This is where Verkooijen hopes to make a difference.
‘Our solution uses aquaculture to turn these barren urchins into a valuable product,’ he says.
‘It captures the urchins from barrens using divers, and puts them in land-based aquaculture systems, where they are fed a high-quality diet for around 12 weeks. 12 weeks is enough to produce large quantities of roe that is of market quality.’
Capturing urchins and removing them from Port Phillip Bay is great news for more than just the urchin roe enthusiasts out there. Verkooijen says that an emerging aquaculture industry will ‘create local jobs and generate economic returns’, but the biggest benefits are ecological. By reducing the overabundance of short-spined purple sea urchin problem in Port Phillip Bay, Verkooijen says the biggest beneficiary should be the golden kelp.
‘Kelp forests are the foundation of the ecosystem in Port Phillip Bay,’ he says. ‘When urchins are removed, kelp forests can return, with the help of active kelp restoration. This will improve the biodiversity of the bay, help battle climate change and boost fishery production. Kelp forests are also beautiful to swim, snorkel and dive in, supporting the local tourism industry.’
Urchin overabundance isn’t just a Port Phillip Bay problem, or even a uniquely Australian one. But, with Verkooijen’s aquaculture research, there’s an opportunity to correct the purple sea urchin overabundance problem while also supporting a growing urchin roe industry.
‘There are many places in the world, like Norway and Canada, where sea urchins have become overabundant in the last decades,’ Verkooijen says. ‘Our research shows that “roe-enhancement aquaculture” is a potential solution to control population numbers of those sea urchin species that are commercially attractive and viable for such an aquaculture industry.’
So, what can we do about Australia’s short-spined purple sea urchin problem? For us everyday consumers, the answer may lie in developing a taste for local urchin roe.
