Mussels mostly handle heatwaves, surprising scientists

One of the oceans’ often maligned creatures, mussels, can survive and recover from marine heatwaves surprisingly well, according to new research published in Marine Biology.

The research found that Asian green mussels (Perna viridis) could speed up their heart rates and change other bodily functions to handle hotter ocean temperatures and return to normal when things cool down.

Although overshadowed as a delicacy by oysters, mussels are also an important food source for many people, and are key to the ecosystems they inhabit. They recycle nutrients and clean large volumes of water by filtering when they feed.

Researchers from the Chinese University of Hong Kong and University of South Australia say this is good news for mussel’s survival as climate change provokes more frequent and intense marine heatwaves.

The researchers collected mussels from Tolo Harbour in Hong Kong: large 5cm mussels, and small 3cm mussels.

They kept them in tanks for several weeks: after a few days for the mussels to adjust, half of the tanks were heated to temperatures 4°C above average for 3 weeks, while half stayed at ordinary temperatures as a control.

This resembles future marine heatwaves expected in the area, according to paper co-author Dr Laura Falkenberg, an environmental lecturer at UniSA.

The researchers monitored the mussels, tracking survival, heart rate, and clearance rate: the rate at which mussels filter water.

“We saw that they were able to survive,” says Falkenberg.

“We didn’t see more mortality in the elevated temperatures compared to the controls, and they were also able to adjust a couple of their physiological responses.”

The results surprised the team: they were expecting changes to the mussel vital signs. The physiological responses likely helped the mussels deal with the high temperatures, says Falkenberg.

“When organisms can adjust heart rate and clearance rate, it allows them to modify their energy acquisition. Hotter temperatures generally mean that you need to use more energy to survive, and it looks like our mussels were able to gain more energy to support those processes.”

The mussels then had another week at ordinary temperatures to cool down.

“We also looked at recovery of the organisms after the heatwave event,” says Falkenberg.

“We saw that the heart rates and the clearance rates of the ones that had been in the hotter water were down similar to the ones that had always been in controlled conditions. So that indicates that they’re then able to readjust the processes when they when the heatwave is over.”

Falkenberg says that it’s likely other mussels and marine species could have similar resilience, particularly in Hong Kong, which already experiences very hot marine conditions.

“We’ve also looked at some other animals like marine snails and urchins, and found that they are also pretty tolerant of these heatwave events – potentially because Hong Kong already experiences quite extreme conditions.”

The researchers are interested in investigating other physiological signs.

“One of the other interesting things in marine heatwave research is that we’re expecting to see events occurring closer together, so more frequently,” says Falkenberg.

“Looking at the effect that subsequent stress events could have could be really interesting in the future as well.”