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Baltic clams, worms release as much greenhouse gas as 20,000 dairy cows

New study shows oceans with worms and clams enhance release of methane into atmosphere up to eight times more than oceans without them.

Scientists have shown that ocean clams and worms are releasing a significant amount of potentially harmful greenhouse gas into the atmosphere.

The team, from Cardiff University in Wales and Stockholm University in Sweden, have shown that the ocean dwellers are producing large amounts of the strongest greenhouse gases — methane and nitrous oxides — from the bacteria in their guts.

Methane gas is making its way into the water and then finally out into the atmosphere, contributing to global warming; methane has 28 times greater warming potential than carbon dioxide, the researchers pointed out.

A detailed analysis showed that around 10% of total methane emissions from the Baltic Sea may be due to clams and worms. The researchers estimate that this is equivalent to the methane given off by 20,000 dairy cows. This is as much as 10% of the entire dairy cow population in Wales and 1% of the entire U.K. dairy cow population.

The findings, which have been published in the journal Scientific Reports, point to a neglected source of greenhouse gases in the sea and could have a profound impact on decision-makers.

It has been suggested that farming oysters, mussels and clams could be an effective solution to human pressures on the environment, such as eutrophication caused by the runoff of fertilizers into waters.

The authors warned that stakeholders should consider these potential effects before deciding whether to promote shellfish farming to large areas of the ocean.

"What is puzzling is that the Baltic Sea makes up only about 0.1% 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," study co-author Dr. Ernest Chi Fru from Cardiff University's School of Earth & Ocean Sciences said.

Lead author Dr. Stefano Bonaglia from Stockholm University 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. These small yet very abundant animals may play an important but so far neglected role in regulating the emissions of greenhouse gases in the sea."

To arrive at their results, the team analyzed trace gas, isotopes and molecules from the worms and clams — known as polychaetes and bivalves, respectively — taken from ocean sediments in the Baltic Sea.

The team analyzed both the direct and indirect contribution these groups were having on methane and nitrous oxide production in the sea. The results showed that sediments containing clams and worms increased methane production by a factor of eight compared to completely bare sediments.

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