SCIENTISTS have warned about the expansion of shellfish farming after finding that clams and worms in the Baltic Sea are giving off as much gas as 20,000 dairy cows.

They are concerned that large amounts of methane and nitrous oxides are being released from the bacteria in their guts.

And they say the impact on the environment has to to be calculated before there is any expansion of the farming of oysters, mussels and clams.

But the report has raised concerns within the Scots shellfish industry that the study authors have taken their conclusions too far.

Aquaculture – the farming of aquatic animals – is one of the fastest growing food production industries in the world.

And some experts thought that bivalves were the best option for farming if choosing to farm and/or eat animals because they appeared to have minimal ecological impact.

Dr Stefano Bonaglia from Stockholm University who led the new study said the small animals on the sea floor may play an "important, but so far neglected role" in regulating the emissions of greenhouse gases in the sea.

The Herald:

How the study illustrated the emissions

He said: Our research looked at the most abundant clam species in the Baltic Sea, which is currently not farmed. Although we did not study oysters and blue mussels, our results may suggest that they have a potential for similar effects on methane emissions.

"The potential impact we are talking about is that clams and worms significantly increase the release of methane from marine sediments, and thus clam farming may enhance greenhouse gas emissions.

"Our warning message is that these potential impacts need to be considered and accounted for before deciding whether to expand shellfish farming or other more sustainable ways of food production."

He added: "It sounds funny but small animals in the seafloor may act like cows in a stable, both groups being important contributors of methane due to the bacteria in their gut."

The Cardiff and Stockholm universities' study found 10% of methane emissions from the Baltic Sea came from clams.

The Herald: Clams with butter beans

The methane bubbles out of the water contributing to global warming as it as 28 times greater warming potential than carbon dioxide.

They suggested worms and clams enhance the release of methane into the atmosphere up to eight times more than oceans without them.

Nick Lake of the Association of Scottish Shellfish Growers believed the study authors in suggesting there are implications for the the expansion of shellfish farming had gone too far.

"It sounds to me like a scientist who is extrapolating too far without the evidence," he said. "Because all the work we have seen on greenhouse emissions from oysters and mussels does not support this at all.

"The thing about the Baltic Sea is there tends to be very more fresh water - it is such a different environment. And they haven't done any work on oysters and mussels.

"The carbon footprint for shellfish production [in Scotland] is so much lower than every other marine or even terrestrial protein source."

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Craig Burton, one of the Scottish regional managers of Seafish, the seafood industry body, agreed that more needs to be found out before any hard and fast conclusion could be drawn.

"It’s an interesting study, but it only looks at two species and conditions akin to the Baltic. Should studies be made on other species under their prevailing conditions, then different results might be expected," he said.

The majority of production in Scotland is centred on mussels but oysters and scallops are also grown.

Farming typically takes place in sea lochs and voes on the west coast of the Scottish mainland, in the Western Isles and Shetland, with the indented irregular coastline of Scotland offering many ideal sites for shellfish production.

Co-author Dr Ernest Chi Fru, from Cardiff University's school of earth and ocean sciences, said: "What is puzzling is that the Baltic Sea makes up only about 0.1 per cent of Earth's oceans, implying that globally, apparently harmless bivalve animals at the bottom of the world's oceans may in fact be contributing ridiculous amounts of greenhouse gases to the atmosphere that is unaccounted for."

The Herald: Kim Hardy hard at work collecting samples from Colchester’s famous oysters

The scientists analysed trace gas, isotopes and molecules from the worms and clams, known as polychaetes and bivalves respectively, taken from ocean sediments in the Baltic Sea.

They analysed both the direct and indirect contribution that these groups were having on methane and nitrous oxide production in the sea.

Results showed that sediments containing clams and worms increased methane production by a factor of eight compared to completely bare sediments.

SCIENTISTS say emissions of the greenhouse gas methane from livestock are greater that previously thought posing an additional challenge in the fight to curb global warming.

Revised calculations of methane produced per head of cattle released at the end of last month show that global livestock emissions in 2011 were 11% higher than estimates based on data from the UN’s Intergovernmental Panel for Climate Change (IPCC).

Cows and other ruminant animals release methane into the atmosphere as a result of a process called “enteric fermentation” — a technical term that basically refers to the digestive chemistry in the animals’ stomachs.

The methane produced in this process is exhaled or belched by the animal and accounts for the majority of emissions from ruminants.

Furthermore, the animals’ waste also fills the atmosphere with methane depending on how it is handled, meaning that “manure management” is categorized as a separate source of methane emissions.

The reports by the IPCC, drawing from thousands of scientists, help leaders take action on climate change, which has begun to wreak havoc on weather around the world.

“Just from livestock methane emissions, our revisions resulted in 11 percent more methane in a recent year than what we were previously estimating,” said Julie Wolf, lead author of the study. “It’s not the biggest contributor to the annual methane budget in the atmosphere, but it may be the biggest contributor to increases in the atmospheric budget over recent years.”

Besides natural sources such as peatland, wetlands and termites, methane from human activity - approximately two-thirds of the total - is produced in two ways.

The odourless and colourless gas leaks during the production and transport of coal, oil and especially natural gas.

In roughly equal measure, it also comes from the flatulence of ruminants such as cattle and sheep, as well as the decay of organic waste, notably in landfills.