How Sydney Harbour’s mussels will respond to increased carbon emissions

Photo credit: Nic Walker

Photo credit: Nic Walker

They say there is nothing so strong it can come between a mother and child, and even when it comes to mussels that is usually the case.

But increasing ocean temperatures and acidification look likely to disadvantage future generations of mussels in Sydney harbour, straining the maternal investment made by adult mussels in their offspring.

In a recently completed study by Western Sydney University, researchers looked at the impact of climate change on biodiversity in Sydney harbour, predicting there will be half as many species living in and around the harbour’s mussels by the end of the century.

“Specifically we were looking at how elevated C02 levels can influence ocean acidification and rising temperatures and how that would affect the communities of species that live among the mussels in the harbour,” said project leader Dr Victoria Cole.

The species in question were all invertebrates, like small prawns, worms and snails, none measuring more than one centimetre in length.

“They are probably the main species that make up biodiversity in the harbour and from an ecological role they are important as a source of food for other species. The mussels are important filters and make the harbour a lot clearer.”

Conducted at the Sydney Institute of Marine Science at Chowder Bay, the year-long experiment was unique because it was one of the first conducted outside of a lab, in a realistic outdoor setting.

It analysed the effects on two species of mussels, the native hairy mussel and the introduced Mediterranean mussel, placing them in conditions predicted for the end of the century by the Intergovernmental Panel on Climate Change.

While current generations of both native and introduced species either grew faster or showed no effect, the experiment showed the offspring of future generations of native mussels will not fare so well.

“Usually a mother will put all of its energy into creating larger eggs so there is more energy for its offspring to grow bigger and stronger, but it is using all its energy to cope with stressful climate change conditions, rather than putting that energy into making bigger eggs,” said Dr Cole.

“Therefore the harbour will experience an overall loss of species [over time] because native mussels are more abundant and provide a better habitat for biodiversity and other species.”

One of the reasons molluscs, like mussels and oysters, will not cope well with elevated C02 levels is because their shells are made from calcium carbonate, which can be dissolved by highly acidic waters.

While the native hairy mussel is not farmed or used for human consumption Dr Cole said the results are telling for all marine species, including those farmed for food production.

In a recent report by the Climate Council, researchers highlighted how Australia’s agricultural markets will be challenged by a warmer climate and changing weather patterns.

The Feeding a Hungry Nation: Climate Change, Food and Farming report said wild fisheries and aquaculture industries across Australia are already being affected by “rising sea levels, increasing ocean acidification, increasing ocean temperatures, changes in the strength and direction of ocean currents, changes in the El Nino Southern Oscillation, increased storm surges, and changing rainfall patterns”.

The report said fisheries production in tropical areas is projected to decline around 40 per cent by 2055 (with increases possible at higher latitudes due to the large-scale redistribution of fish populations).

Lucy Cormack, The Sydney Morning Herald, 23 October 2015. Article.

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