If you’re lucky enough to get down to the beach this summer, you’ll probably notice evidence of a tiny elusive crustacean. Most people never see the sand bubbler crabs that live in burrows along the shoreline and have only seen the purposeful patterns they leave behind.
One Aussie author and photographer has become captivated by the mesmerising installations they leave on the sand as part of their highly refined feeding process. During his travels, John Brock has snapped their short-lived creations in Byron Bay, Cairns and Darwin.
“I’ve taken many photographs of their designs and some of them are amazing. Every single one is unique but it’s wiped clean every six hours during tidal movements,” he told Yahoo News.
The creation and destruction of sand bubbler crabs is something Brock is philosophical about. “Their designs are lost forever, but they’ll produce another one,” he said.
One of the most impressive ‘designs’ Brock has captured was taken at Kewarra Beach north of Cairns. It shows the work of dozens of crabs across the golden sand, with each one forming a pattern similar to the petals of a flower or a newly formed crystal.
Another image taken at East Point Beach in Darwin shows a single crab burrow next to a more simplistic pile of sand balls being swallowed by the tide.
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Sand bubbler crab patterns at Byron Bay resemble seaweed. Source: John Brock
How do the crabs create balls of sand?
Sand bubbler crabs wait out the high tide in a burrow that contains a bubble of air, but after the water recedes they wander around the surface to feed. This specialised process involves filtering the sand through their mouthparts in search of microorganisms and discarding the unwanted grains in lines along the sand.
Peter Davie, the curator of crustaceans at Queensland Museum explained to Yahoo they’re important in keeping the beaches clean by digesting and processing organic detritus in the sand.
“Every time the tide comes in, the beach is being replenished with organic material and it mixes into the sand,” he said.
“Open sandy beaches are very nutrient-poor, which is why they need to process large volumes of sand to get enough food to live on.”
There are over 20 recognised species of sand bubbler crab around the world, including this on photographed in Malaysia. Source: Getty
Are the patterns completely random?
One of the few people to study what drives the formation of sand bubbler crab patterns is Jane Prince, an Honorary Research Fellow and the University of WA’s School of Biological Sciences.
She was involved in a 2010 study that examined a species living at Cable Beach in Broome. They found there was nothing random about the way the patterns were formed, and several factors were influencing their design.
They recorded the crab exiting its burrow and making a groove in the sand. It would continue to place the balls in a straight line along the groove until its gill chamber was empty – this internal reserve of water is what allows it to breathe on land. After the crab returned to its hole to replenish itself, it would begin a new line, usually in the same direction as the last.
“By radiating out their pattern of balls, they’ve always got a fresh supply of sand with food in it,” Prince said.
Predators were another factor that influenced the size and shape of the crab’s creations.
“The whole idea of running back to a central burrow means it’s never too far away from safety. It can go back to the burrow when it’s disturbed by predators. And that’s mostly wading birds, particularly red-capped plovers, so if they see those or a human, they’ll immediately run back into the burrow,” Prince told Yahoo.
“So if they’re continually disturbed by predators then the lines won’t go as far.”
East Point Beach in Darwin is home to sand bubbler crabs. Source: John Brock
Another impact on the shape of patterns is the density of the crabs, and that’s because they don’t like to run across the lines of their neighbours. Surprisingly this behaviour isn’t driven by the crabs being territorial, instead it’s about avoiding sand that’s already been filtered and denuded of nutrients.
“There wouldn’t be any point in crossing over. So you tend to get discrete patterns that aren’t interwoven. There are specific boundaries, and you can trace which area belongs to each crab,” Prince added.
Sadly the project’s research leader died, and the sand bubbler crab study ran out of money. Since then there has been little investigation into its pattern-making, and questions about where it chooses to create its burrow remain unanswered.
Documenting crabs leads to bigger life lesson
Brock interest in crabs remains a hobby. His professional life has focused on plants, and he’s the author of Native Plants of Northern Australia, 2022. The beach has been a place of escape and wonder, particularly the intertidal zone, where he loves to “beach roam” for weathered objects like shells, stone and wood.
“Rather than pick them up, I thought why don’t I just photograph them and leave them on the beach for everyone to enjoy,” he said.
His wanderings around the intertidal zone are what led him to the bubbler crab. While he’s yet to make any scientific observations about the species, by documenting them he’s learned valuable lessons about life.
“To see these patterns – to look at them and preserve them is just mesmerising. They’re creating brilliant art without it actually being art,” he said.
“It’s nature’s art, and many of us have seen this in various ways, in flowers and leaf patterns. Sand bubbler crabs are something tiny and ephemeral. And these little creatures are another reason to look after the beaches and do better when it comes to protecting nature.”
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