Photo caption: University of Canterbury post-doctoral fellow Dr Spencer Virgin is studying how limpets are adapting to warmer temperatures in New Zealand.
Dr Spencer Virgin, a post-doctoral fellow at Te Whare Wānanga o Waitaha | University of Canterbury (UC), has worked on a thesis project he has dubbed 'hot limpets', exploring how these common shellfish cope with a warming climate.
Dr Virgin, from the UC School of Biological Sciences, found that as temperatures rise, limpets move towards cooler, south-facing rock surfaces to avoid overheating in the sun, with some of them moving up to five metres as the crow flies - up to 150 times their body length - to find shade.
"This behaviour means they're quite resilient to the kind of extreme heat events that are becoming more common," Dr Virgin says. "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. As a result of this adaptive behaviour, I think the long-term resilience of these species is quite secure. It's not all doom and gloom for limpets because thankfully, they're quite resilient and adaptive to heat stress."
Dr Virgin carried out this research in Kaikōura, North Canterbury, and his first step was to find out the thermal tolerances of limpet species living in the area. To do this, he deployed 'robo limpets' - an empty limpet shell filled with silicone gel and a tiny temperature logger. He also built portable heart rate monitors for limpets so that he could 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. The second step was looking at how they respond to that kind of heat stress in the field," he says.
Starting in 2022, he attached micro tags to about 850 limpets around boulders in Kaikōura. He visited these 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.
Dr Virgin says limpets are grazers so they play an important role in the healthy functioning of marine ecosystems by maintaining bare space. "They eat micro and macro algae, which form those 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."
Dr Virgin, who is Canadian, says local limpets are "super cool". "New Zealand probably has more species of limpets than almost anywhere else in the world - we've got a lot of big limpets here. 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."
He says they have another quirky feature in that they are able 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 this behaviour, small limpets of some species will live on top of the bigger ones so they don't get bulldozed."
Dr Virgin is furthering his research under a Ministry of Business Innovation and Employment-funded programme assessing stressors to the marine ecosystem, led by UC Distinguished Professor David Schiel and University of Waikato Professor Chris Battershill. Dr Virgin is assessing 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.
