Mussels and oysters could be off the menu by the end of the century according to some scientific predictions.
Just imagine: no more clinking of mussels in a spicy tomato broth with warm crusty loaf: no more chilled plump, creamy oysters washed down with bubbly.
What’s going on?
Unfortunately, marine researchers believe the shellfish favourites could become victims of global warming and its concurrent effect on rising sea acidity levels.
Some estimates suggest some 500 billion tonnes of carbon dioxide may have been absorbed into the oceans over the past 200 years. That makes it more acidic. And it then acts like osteoporosis on the shells of mussels and oysters. Their shells become thinner, growth slows and more of them die.
Researchers at have established that a mussel’s ability to grip to a rock or rope could be loosened by an increase in the ocean’s pH balance.
This could result in them effectively losing their grip on life, falling off their attachment and sinking to the bottom of the ocean before they can grow to harvestable size.
And oysters could be impacted by the corrosive effect of water, particularly on the shells on oyster larvae (seed) and a loss of their nutrients, which would impact their ability to survive
Lead researcher Professor Emily Carrington predicts that by 2100 coastal regions where mussels currently thrive will pass an acidity threshold beyond which farming will be unviable.
“Our early laboratory studies showed mussels made weaker attachment threads when seawater pH dropped below 7.6,” Professor Carrington says.
The academic says that some 20 per cent of mussels currently fall off their attachment, but this rate could increase to 40 per cent with increased sea acidity levels.
“We conclude that mussels rely on the high pH of seawater to cure their adhesive effectively and form strong attachments,” Professor Carrington says.
While that prediction would cause alarm in the waters off America’s North West coast, what might it mean for Australia’s mussel and oyster producers?
There are more than 20 mussel farms spread across southern Australian coastal marine waters in Tasmania, Victoria and South Australia. They produce about 3000 tonnes of the molluscs each year worth nearly $10 million.
Pacific and Sydney Rock are farmed from Queensland to Western Australia. Some 15 tonnes are produced annually with a value of around $100 million.
One of the CSIRO’s senior research scientists says that while ocean acidity level could contribute to mussel decline, it was important to consider all the stresses that might be placed on a marine ecosystem.
“There could be a situation where we get a ‘perfect storm’ of stresses,” says Doctor Andrew Lenton of the .
“Aside from the acidity level impact on their attachments, mussels could also be impacted by thinning shells, increased risk of disease, environmental damage and the effects of overall global warming,” he said.
The research scientist said that it was going to be important to understand the ability of mussels to adapt to changing conditions.
“How resilient are they to these changes in conditions? Is there anything we can do to improve that resistance? Can we help create adaption strategies,” Doctor Lenton says.
President of the , Andy Dyer, says that ocean acidification is not a driving issue at present.
“It’s one to keep an eye on, but we’ve got a range of current operational issues that need our attention on a daily basis,” he says. “We’re at the mercy of the elements as far as retention is concerned (keeping mussels attached to lines).
“Water temperature, food availability and the amount of sediment are our main challenges. Then there’s the level of sunlight and variations in salinity levels,” Mr Dyer says.
The veteran mussel grower said the industry would keep abreast of research, but in the meantime it would be business as usual.
President of the , Judd Evans, says the industry is aware of the acidification issue and is liaising closely with the relevant scientific and government agencies.
Oysters as usual - for now: the potential problem is a long way off, although the industry is already addressing the issue. Source: Alan Benson
“Obviously, the end of the century is some way off, but this is an important industry and we need to be working out how we can address an issue like acidification,” he says.
“Moving the farms to other locations isn’t really an option. We’ve spent a long time investigating prospective locations all along the coastline – where we are now has proven to be the most productive.”
Mr Evans says a potential key in addressing the issue probably lay in the “bloodlines” of certain oyster families.
“We’d be looking to identify the ones that demonstrate a certain resilience to acidification and then concentrating on breeding those into the production line,” he says.
“It’s a delicate balance because we believe we have the perfect oyster attributes at the moment, nice, deep and plump.
“We’ve got to retain those qualities while we also develop the resilience that will ensure the industry’s ongoing viability,” Mr Evan says.
One thing is for sure: the mussel and oyster industries can be sure of plenty of public support to keep these mealtime favourites firmly on the menu.
