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If you want to see a whole town flex its mussels, head to Portarlington on the Bellarine Peninsula. Each year, the Portarlington Mussel Festival takes over the tiny bayside town to celebrate the shellfish that has made it famous, bringing music, art, wine and, naturally, plenty of local mussels to the table. ‘
There’s a problem, though: climate change and interactions between native and non-native lineages means those mouthwatering molluscs – and an iconic food festival – may not be around forever.
This is where Deakin University graduate researcher Alex Berry hopes to make a difference. Berry’s research focuses on the impacts of climate change on blue mussels, and the way our native species interact and interbreed withother blue mussel lineages. We asked Berry to shed more light on this issue.
The scientific definition of mussels classifies them as molluscs, a diverse group or ‘phylum’ that also includes octopus, squid and cuttlefish, as well as garden variety snails and slugs. Mussels belong to a class of molluscs called bivalves, meaning that they have a two-part hinged shell. There are both sea mussels and freshwater mussel species in Australia. For Berry, the focus is on just one: Australia’s blue mussel.
‘The blue mussel inhabits the southern part of Australia as far north as Sydney,’ says Berry. ‘They tend to live on rocky shores, attached to rocks and each other by little threads called byssus, in the area between the high tide and low tide marks. They are able to thrive here because when the tide goes out, they can press their shells together, shutting themselves off from the environment and preventing themselves from drying out while they’re exposed.’
Mussels are also commonly farmed for food, with Victorian farms alone producing 1700 tonnes of blue mussels each year.
Mussels may seem like mild-mannered molluscs, but they play a vital role in our marine ecosystems. According to Berry, there are three main environmental benefits of mussels:
1. They provide a habitat for other species: Mussels naturally band together in what Berry calls a ‘complex three-dimensional structure’, creating safe spaces where other organisms can thrive.
‘Barnacles and algae grow on the shells of mussels, and little fish, crustaceans and other organisms live on these mussel reefs,’ Berry says. ‘Not only that, but there’s a special little type of crab, the pea crab, which lives inside the mussel shells themselves.’
2. They clean the water around them: Bivalves like mussels are filter feeders, meaning they draw in water through their shells and filter out particles for food. This process helps improve water quality, benefitting surrounding plants and animals.
‘This is mostly algae, which – if it’s too dense – can make the water look greenish brown,’ says Berry. ‘With clearer water, more light can permeate the water and allow things like seaweed and seagrass to grow more efficiently.’
3. They provide a food source: Perhaps not good news for mussels, but their position at the bottom of the food chain is vital for the ecosystem.
‘Lots of marine animals, including crustaceans and birds, like to eat mussels,’ Berry says. ‘They’re right at the bottom of the food chain, consuming primary producers and providing an animal food source to consumers, like us.’
Berry adds that mussels are one of the more sustainable sources of protein that we humans can opt for. ‘They’re one of the most eco-friendly animal protein sources out there, with one study suggesting they produce forty times less carbon dioxide per gram of protein compared to beef.’
Mussels aren’t classified as endangered in Australia, but that doesn’t mean they don’t face an existential threat. For Berry’s Australian blue mussels, there are two clear dangers:
1. Climate change: Australian mussels thrive in colder water, and sadly, that environment is already changing due to climate change.
‘With climate change, the Australian coastline is warming up quickly. The water of the southeastern coastline, where we find a lot of these mussels, is actually the fastest warming area around Australia,’ Berry says. ‘This has the potential to contract the species’ range towards the south, pushing them out of northern areas where the water is becoming too warm.’
2. Interbreeding with non-native blue mussels: European blue mussels are an introduced species and, unlike their Australian mussel counterpart, are quite well-adapted to warmer water – meaning they may outcompete their native relatives.
‘You can’t tell the European and Australian mussels apart just by looking at them – we need genetic testing just to tell what’s what,’ says Berry. However, there may be a silver lining to these interactions, as some hybridisation between the different genetic lineages may allow for greater resilience to a warming climate.
Berry’s research focuses on the effects of elevated seawater temperatures due to climate change, and Australian mussels are certainly feeling those effects.
‘At high temperatures, mussels shut their shells, just like they do when out of water, which might be a response to stress,’ he says. ‘This means they aren’t feeding, and is generally a sign that the mussel isn’t too happy. However, when they’re closed, mussels use much less energy, so this might work well as a strategy for short, hot periods.’
The effects of climate change go beyond temperature. In the past 200 years, ocean pH has decreased by 0.1 units, marking a 30% rise in acidity. This is another climate-induced battle facing mussels, according to Berry.
‘Mussels are affected by ocean acidification, as their shells are made up of calcium carbonate, which is vulnerable to being dissolved in acidic water,’ he says.
So, how might the introduced genetic mussels’ lineages affect Australian mussels? Berry’s research proposes that, rather than being replaced by the more climate-adjusted European blue mussel, Australia’s population might benefit from interbreeding with it to enhance its heat tolerance. And, thanks to some genetic quirks, it seems like a promising plan.
‘The textbook definition of a species doesn’t quite apply to blue mussels,’ Berry says. ‘There are a few closely related blue mussel species that can interbreed and produce fertile offspring. Our genetic testing of the mussels we have sampled in Australia shows that there has already been extensive interbreeding between the European and Australian blue mussels. All the populations northwards from Lakes Entrance in eastern Victoria are dominated by hybrids – what we call the offspring when they have both Australian and European ancestors.’
There’s a problem, though: while genetic hybrids exist in the wild, Berry says that creating a mix of Australian and European hybrid mussels in controlled settings is tougher. This makes it difficult to fully understand the compatibilityof these two lineages.
‘Australian native mussels and hybrids between Australian native mussels and introduced Mediterranean mussels occur on different areas of the Australian coastline,’ Berry says. ‘The presence of the hybrids themselves indicatesthat the genomes of the two parental lineages, Australian mussels and Mediterranean mussels, are compatible.
‘However, in these complex reproductive systems, compatibility can break down in subsequent generations, between hybrids backcrossing with one of their parental lineages. We have sometimes found it hard to find populations of the Australian and hybrid mussels that are ready to reproduce at the same time, which makes investigating these interactions difficult.’
On this front, Berry hopes to find a solution.
‘Our research focuses on crossing these hybrids with native Australian mussels to see if we can work out what is preventing full genetic mixing,’ he says.
From filtering algae-filled water to providing a reliable food source at the bottom of the food chain, Australian blue mussels are a vital part of Australian marine ecosystems. As they face the increasing threat of climate change, though, our native Australian mussels are going to need help.
By researching how interactions between different genetic mussel lineages and climate change interact to affect Australian populations, Berry hopes to find a way to safeguard these beautiful bivalves.
‘By studying the thermal performance of hybrid mussels, and how easily they can crossbreed with the native mussels, we hope to be able to see how these populations may change into the future,’ he says.
If these hybrids are able to inhabit the warmer waters that are occurring due to climate change, without pushing the native mussels out of cooler areas, these hybrids may be able to continue providing ecosystem services that would otherwise have been lost if native Australian mussels couldn’t cope with the heat: a phenomenon known as evolutionary rescue. An exciting potential case of some good coming from an introduced species.’
Graduate Researcher,
Faculty of Science Engineering & Built Environment,
Deakin University
