The colourful world of Australian sea urchins
HEART urchins – heart-shaped, as their name suggests – are widely distributed around the Australian coastline, including offshore territory such as Lord Howe Island. There, Breynia australasiae live beneath the sand of the island’s pristine lagoon beaches, where their skeletons eventually wash up on the shore.
In 1982, Ashley Miskelly’s mother travelled to Lord Howe Island and on her return, showed him a heart urchin skeleton, or test, white and intricately patterned – fascinating for a young 14-year-old boy. “She asked me what I thought of it, and from then onwards I’ve been interested in them,” Ashley says.
Now an urchin specialist and Australia’s only echinoid taxonomist, Ashley came across heart urchins again while studying palaeontology in high school. This one was a fossilised specimen, but still similar to the one his mother first brought back from Lord Howe. “I got taken in by it and it’s just been that way ever since. They’re attractive-looking things,” he says.
As of 2018, Ashley has been studying not only Australian but the world’s sea urchins for 32 years. He’s contributed to scientific papers – on their taxonomy, behaviours and response to climate change – and written two books: Sea Urchins of Australia and the Indo-Pacific, a field guide, and Sea Urchins of the World – Diversity, Symmetry and Design, a coffee-table book.
One of his greatest achievements, however, was the establishment of the Sea Urchin Science Centre and Gallery in Kurrajong, NSW, which holds a scientific collection of approximately 400 sea urchin species, all professionally curated. “I had a friend who came to the centre for the first time just recently and he couldn’t believe what he was seeing,” he says.
The papers, books, gallery and laboratory all contribute to Ashley’s ultimate goals of advancing our knowledge of these poorly understood sea creatures and getting more people interested in the bizarre lives of what Ashley calls “nature’s vacuum cleaners”.
The fossil record of sea urchins dates back to the late Ordovician period, 450 million years ago. Early Jurassic urchins were the ancestors of the bilaterally symmetrical heart urchins and sand dollars we know today. “These urchins sit under a layer of soft sediment, which is perfect for fossilisation. They become compacted and then they calcify so they’re very well preserved. We have a lot of fine examples of these types of fossil sea urchins in Australia,” Ashley says.
The Jurassic saw a change in habitat when radially symmetrical sea urchins ventured from hard to soft substrates, eventually adapting to live in the sand. Around this same time, the mouth moved forward and the anus moved backwards, which allowed the urchin to move forward. This also made it easier for the creature to swallow sediment.
Once denuded – where nothing but the skeleton is left – most sea urchins reveal hypnotic patterns and colours.
One of Ashley’s favourite sea urchins is Phyllacanthus irregularis, an often crimson-coloured species with thick, pencil-like spines. “I painstakingly removed all the spines, soft tissue and organic material and it revealed a perfectly symmetrical pattern,” Ashley says. “It’s a miracle of life. I like them all, but that one sticks out; you have to see it to believe it.”
Possibly the rarest colour for a sea urchin is yellow, and Ashley has only seen it once in a variation of the seagrass sea urchin (Holopneustes inflatus), a perfectly spherical animal that sometimes has “saffron yellow” spines, skeleton and jaw system.
And it’s not just the colour and skeletal shapes of sea urchins that are diverse – the spines are also different from species to species. The needle-spined sea urchin, for example, has spines that can grow to 40cm. The thorny-spined sea urchin, a species that calls Vaucluse Bay in Sydney home, has thorny spines used to attract marine growth for camouflage.
Worldwide, there are currently around 1300 species of sea urchin known to science, of which 330 exist in Australian waters. According to Ashley, he has recorded 53 species in Sydney Harbour alone, while other rare species can be found in Botany Bay, too. “Sydney Harbour is a hub because of the habitat: nutrient-rich, fine sands, coarse shell grit, rocks, caves, kelp and seagrass. Sea urchins aren’t as common around rough coasts, they prefer calm bays.”
Visitors to Ashley’s urchin science centre are always surprised by the diversity of colour and shape, he says. “They’ll say, ‘I never knew there were so many, and I didn’t know they were so colourful’, or, ‘I’m surprised anything is down in Sydney Harbour, with all the runoff and pollution’.”
The urchins are of great importance to their local ecosystem, Ashley explains. “Radially symmetrical sea urchins, like the black sea urchin, control the growth of algae in the harbour. Heart urchins are important ecologically because they’re sediment-swallowers, so they eat anoxic sediment and pass the clean sand back into the environment. The flat sand dollars sit on the sand and act as a type of vacuum cleaner, making sure everything is in balance.”
The world’s smallest sea urchin, Fibularia nutriens, lives in Sydney Harbour. This species is about one third of the size of a rice grain and its breeding behaviours are bizarre in comparison to other urchins. “The females have a horseshoe-shaped brood chamber and they look after the juveniles until they’re developed, then they hop out into the sediment,” says Ashley.
Prior to Ashley’s discovery of the species in Sydney Harbour at a depth of 5m, it was thought the tiny urchin only lived in waters off Cronulla, at depths of around 150m. “They’re easy to miss, but I deliberately go out to look for these things. Otherwise no one would have realised it wasn’t such a deep-water species. It’s important to get these things right,” he says.
Climate change: victim or benefactor?
For the past 23 years, Ashley has focused on studying the sea urchins of Sydney Harbour and Botany Bay. In 2011, he started to notice some significant changes. “Urchins that were once restricted to Queensland waters are now found in Sydney Harbour. One urchin I’ve been monitoring since 2011, Clypeaster reticulatus, was once restricted to north of Moreton Bay in south-eastern Queensland.” The reason? Climate change.
According to Ashley, we’re yet to see any negative impacts from these new arrivals, as he says they’re not competing with anything for food.
In 1978, the black sea urchin was listed as an invasive species in Tasmania and was later blamed for the destruction of the state’s kelp forests. The impact of climate change on sea urchins still requires further research.
It’s hard to say if there’s anyone who will take over Ashley’s work once he retires. “Someone needs to come along with an absolute passion. These kinds of people come around every 100 years,” he says.
“I’m wondering whether or not a lack of support in science generally will mean these people won’t be able to sustain it. It’s not a money-making thing.”