With modelling already linking marine heatwaves to poorer yields of New Zealand’s green-lipped mussel – today accounting for more than $300m in annual export earnings – scientists have been eager to learn what a warmer future means for the species. Photo / Niwa
With modelling already linking marine heatwaves to poorer yields of New Zealand’s green-lipped mussel – today accounting for more than $300m in annual export earnings – scientists have been eager to learn what a warmer future means for the species. Photo / Niwa
A lab glitch has unexpectedly handed scientists important new insights into how one of our most valuable export products may fare with climate change.
Marine heatwaves, which have pushed up our coastal sea surface temperatures by an average 1.6C over the past two years, are predicted to growlonger, stronger and more frequent as the planet warms.
They’ve already been linked to cascading impacts at sea and on land here, from mass sea sponge die-offs and tropical fish drifting into normally colder climes, to big glacier melts, summer heatwaves and unusually early grape harvests.
With projected modelling already linking marine heatwaves to poorer yields of New Zealand’s green-lipped mussel – a product today accounting for more than $300m in annual export earnings – scientists have been eager to learn what a warmer future means for the species.
Mussels were particularly vulnerable in their natural environment during marine heatwave events, as they couldn’t move to cooler waters when their habitat grew too hot.
Research has shown that higher water temperatures weakened mussel physiology – making it easier for pathogens to infect and kill them – while also leaving them skinnier, with less flesh for consumers.
Still, they had shown themselves to be surprisingly resilient.
“Mussels are fascinating creatures with very clever adaptative mechanisms, and have impressed us with their abilities to deal with changing water temperatures,” said Dr Leonie Venter, of the Auckland University of Technology’s Aquaculture Biotechnology Research Group.
Scientists have been investigating how New Zealand’s green-lipped mussels – pictured here in a temperature-controlled tank at Nelson’s Cawthron Aquaculture Park – will fare under climate change. Photo / Auckland University of Technology
One recent international study revealed how a close relative of our green-lipped mussel was able to adjust its heart rate to cope with marine heatwaves.
Other local research has demonstrated how, when under stress, mussels drew on stored-up biochemical resources normally used for growth or reproduction to provide them enough energy to survive.
But they could only do that for so long: and with those special resources sapped, mussels eventually began dying.
Now, a first-of-its-kind study, led by Venter and carried out by a multi-disciplinary research team in wet laboratories at Nelson’s Cawthron Aquaculture Park, has enabled scientists to track such changes over time and temperature.
“Towards the end of the experiment, it was found that areas such as the metabolism, immunity and condition were indeed compromised due to the heat stress,” Venter said.
“Yet, a large portion of the experimental animals were still alive and actively fighting the changing conditions, demonstrating the adaptive capabilities of mussels.”
Venter said the aim of the experiments – undertaken in special tanks mimicking the mussels’ normal environment – had been to monitor physiological responses as the scientists slowly increased the water temperature using submersible heaters.
“As scientists, we strive to keep conditions controlled, but some of the most insightful findings from this study resulted due to a technical issue,” she said.
“Towards the middle of the experiment, a controller malfunction interrupted the temperature ramping procedure, causing an unintentionally rapid increase in temperature for several days.
Dr Leonie Venter, of the Auckland University of Technology’s Aquaculture Biotechnology Research Group, pictured with mussel tanks at Nelson's Cawthron Aquaculture Park. Photo / Auckland University of Technology
“This happened on Christmas Day so, between the holiday vibes and skeleton staff, the glitch was picked up slowly.”
By the time the team had noticed the problem, the water temperature had already risen to 26.5C, causing a large number of the mussels to die.
“But the surviving animals became the gems of the experiment - and demonstrated the adaptive capabilities of mussels’ physiological mechanisms,” she said.
“These surviving mussels have become perfect candidates for selected breeding strategies.”
In another take-away, the team found sustained seawater temperatures of 22C to 25C were enough to make mussels vulnerable – offering a threshold at which point mussel farms could be moved to colder, deeper waters.
Looking forward, Venter saw many more critical questions to tackle.
One was how mussels recovered after they’d sweltered through marine heatwaves – and whether their normal biological state was left permanently altered.
“Also, it remains to be seen, what happens to mussels if they experience a second marine heatwave?” she said.
“For example, how would the surviving animals respond if another marine heatwave emerges in a couple of weeks?
“By answering questions like these, it will highlight which management tools or strategies are required to deal with the effects.”
Jamie Morton is a specialist in science and environmental reporting. He joined the Herald in 2011 and writes about everything from conservation and climate change to natural hazards and new technology.
