A group of scientists from Cardiff and Stockholm Universities reveal that ocean clams and worms are releasing a significant amount of potentially harmful greenhouse gas into the atmosphere. A detailed analysis of trace gases, isotopes and molecules from worms and clams was made from ocean sediments in the Baltic Sea. Having looked at both the direct and indirect contribution of methane and nitrous oxide production, the results showed that around 10% of total methane emissions in the Baltic Sea may be due to clams and worms.

The findings, which have been published in the journal Scientific Reports, point to the significance of this lesser-known source of greenhouse gas emissions. Although this only equates to the amount produced by 20,000 cattle, (about 1 percent of the UK dairy cow herd), the Baltic Sea represents only a tiny fraction of the world’s oceans in which such species are found.

Methane has become a hot topic of concern for many environmentalists, with a warming potential 28 times greater than carbon dioxide. Headline methane-emitters are most commonly cud-chewing ruminant animals like cattle and sheep. Much like ruminants, clams and worms release methane and nitrous oxide from the bacteria in their intestines via the process of flatulence. These gases then make their way into the water and subsequently into the atmosphere, contributing to global warming.

The results of the report are especially interesting given the growing perception that farming more bivalves – oysters, mussels and clams, rather than fish, shrimps and octopus – could provide sustainable sustenance for the world’s growing population whilst reducing overfishing. Many argue that if we are going to continue to farm fish, it would be best to farm those that are as “plant-like” as possible – requiring no additional fish to be caught for feed, no conversion of habitat, and species which experience the least amount of pain and suffering in captivity. At first glance, bivalves do fit this bill. Because of this, scientists have been calling for aquaculture to focus on species such as these, lower in the food web which require little to no feed. There is also agreement among them that aquaculture must reduce its reliance on wild fish inputs and adopt more “ecologically sound management practices”.

Previous reports have identified the multi-faceted benefits of farming bivalves, which include minimizing ecological damage and increasing food security. In addition, the by-products of crustaceans and bivalves can be utilised “efficiently” according to the FAO, with a wide range of applications for shells, including usage in water treatments, cosmetics, food and beverages, as well as pharmaceuticals and, interestingly, in some agrochemicals. Pearl powder created from processed shells is also often used as a diet supplement in feeding livestock and poultry.

A report by the FAO shows that Europe produced 632,000 tonnes of bivalves in 2014, with Spain, France and Italy its major producers. Bivalve culture in China was about 12 million tonnes in the same year, five times the quantity produced by the rest of the world. Other major Asian bivalve producers include Japan, Korea and Thailand. In contrast, this “less-costly production of non-fed aquaculture” is largely undeveloped in Africa and Latin America, however the FAO argue it may offer potential, through species diversification, to improve national food security and nutrition in those regions.

Despite the proposed benefits of bivalve farming, the scientists behind the Baltic Sea study warn that although farming oysters, mussels and clams could help to reduce human pressures on the physical environment, stakeholders should consider the potentially damaging impacts, such as increasing methane emissions, before deciding whether to promote bivalve farming on a larger scale.

Co-author of the study Dr Ernest Chi Fru, from Cardiff University’s School of Earth and Ocean Sciences, said: “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.”

Similarly, chief scientist behind the report, Stefano Bonaglia, claims the “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”. Shellfish, he explains, have been releasing these gases long before global warming became a topic of concern, however he believes that the recent level of emissions may have been exacerbated by the enrichment of coastal waters, caused by the fertilisers found in agricultural run-off.

Whilst this report may offer up sea clams and worms as an alternative place of blame for methane production, it is clear that the industrial up-scaling of natural systems is simply not sustainable. Whether on land or at sea, intensive farming practices magnify processes which occur naturally by creatures great and small. Our approach must surely be to manage food production in such a way that all food species are farmed in harmony with the environment and as an integral part of their ecosystems, not in ways which ultimately destroy them.

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