Humble limpets clinging to the rocky shores around Aotearoa (New Zealand) have proven themselves to be surprisingly savvy when it comes to climate change adaptation, with some species able to move up to 150-times their body length to avoid the sun and find shade.

These are the findings of a new study looking into a thesis dubbed by researchers ‘hot limpets’ and exploring how these common shellfish – marine life abundant across the New Zealand coastline – are coping with a warming climate.

The study has been led by Dr Spencer Virgin, a post-doctoral fellow at Te Whare Wānanga o Waitaha, University of Canterbury, who found that as temperatures rise, limpets move towards cooler, south-facing rock surfaces to avoid overheating in the sun. 

He found that in some cases, these limpets were moving up to five metres to find shade, the equivalent of 150 times their body length.

“This behaviour means they are quite resilient to the kind of extreme heat events that are becoming more common,” said Dr Virgin. “The most interesting thing to me is that limpets are smarter than people give them credit for.

“They know that when temperatures start to rise in spring, they need to go into the shade and wait until it’s cool again before they can come back out.”

It’s as a result of this behaviour that Dr Virgin trusts that the long-term resilience of the species “is quite secure”. 

“It’s not all doom and gloom for limpets because thankfully, they’re quite resilient and adaptive to heat stress.”

Findings like these are important. Limpets are, after all, grazers which means they play an important role in the healthy functioning of marine ecosystems by maintaining bare space. Essentially, they eat both micro and macro algae, which form the slippery biofilms that grow on rocks in the intertidal zone.

“After the Kaikōura earthquake, for example, there weren’t many grazers and pretty much the whole coastline turned green because there was algae all along it. But then, when the limpets and other grazers came back, they kept that algal growth down,” said Dr Virgin.

The researcher carried out his project in Kaikōura, North Canterbury where his first step was to find out the thermal tolerances of limpet species living in the area. To do this, he deployed ‘robo limpets’ – empty limpet shells filled with silicone gel and a tiny temperature logger. He also built portable heart rate monitors for limpets to measure how heat stress affects their heart rates.

“I wanted to find out what temperature is too hot for the suite of limpet species we have in New Zealand, especially the four main ones in Kaikōura,” said Dr Virgin. “The second step was looking at how they respond to that kind of heat stress in the field.”

Starting in 2022, he attached micro tags to around 850 limpets around boulders in Kaikōura. He visited three limpets every two weeks for one year to measure what direction the limpets were facing to see if they were moving in response to changing temperatures.

Such an undertaking would, of course, require a deep affinity for limpets, something Dr Virgin is not short of. 

“New Zealand probably has more species of limpets than almost anywhere in the world – we’ve got a lot of big limpets here,” he said. “ I think there are 15 or 20 species of limpets in New Zealand, including one exceptionally large egg-laying, air breathing, limpet that’s common on the West Coast.

“It’s amazing how resilient to heat stress limpets are. Some of them don’t really show any effects of heat stress until 38 or 39°C, so their thermal tolerances are exceptionally high.”

Another quirky feature of limpets is their ability to slowly “bulldoze” other shellfish and barnacles out of their path using their shell. 

“If something settles too close to a limpet, like a barnacle or something, they’ll put the edge of their shell down and kind of bulldoze that animal out of their way. To deal with thai behaviour, small limpets of some species will live on top of the bigger ones so they don’t get bulldozed,” said Dr Virgin.

Furthering his study of limpets, Dr Virgin is now assessing the differences between North Island and South Island limpets in terms of heat exposure and thermal tolerance. He is also investigating why a cold-water limpet species that was present in Kaikōura until the early 2000s is no longer found anywhere north of Oamaru.

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