Mussel farming to the rescue - mitigating eutrophication in the Baltic Sea

Farming of blue mussels is a new, exciting solution to an old problem – eutrophication of the Baltic Sea. Mussels filtrate, extract nutrients and improve water quality, which may reduce the frequency of algal blooms. Consequently, mussel farming is being tested as an environmentally responsible tool to reduce Baltic Sea eutrophication. The farmed mussels could potentially be used as a replacement for fish meal or soya meal to feed poultry or farmed fish as well as for bioenergy production. As a response to a new study that suggest that mussels emit substantial quantities of methane, two scientists from the BBG project decided to set the record straight. 

Farming of blue mussels has the potential to be a new solution to an old problem – the eutrophication of the Baltic Sea. Eutrophication is caused by excess nutrients from industrial and municipal waste-waters as well as agricultural activities around the Baltic Sea. Despite tremendous efforts and advances made in recent years to control inputs from wastewater treatment plants and agriculture, there are still far too many nutrients in the Baltic Sea. While we need to continue efforts to reduce influx, we also need to start actively removing nutrients from the Baltic Sea. Studies in other regions have shown that cultivating and harvesting blue mussels (Mytilus edulis) can substantially improve water quality. This solution is currently attracting a lot of interest as well as investments in research and technology development. However, there is a need to ensure that mussel farming is a sustainable and environmentally responsible way to improve water quality.

Last week, a new study suggested that mussel farming could add significant amounts of methane, a powerful greenhouse gas, to the atmosphere. The statement was based on extrapolations from laboratory experiments conducted on sea worms and the Baltic Clam (Limecola balthica), living in carbon-rich Baltic Sea sediments. These ocean critters are very common in the Baltic Sea, and their combined methane emissions were calculated to be equivalent to 20,000 dairy cows.

Dr. Martyn Futter, from the Swedish University of Agricultural Sciences (SLU), agrees that any suggestion that more intensive mussel farming may cause harm to the environment must be taken seriously, given the need for environmentally friendly methods to control nutrients in the Baltic Sea.

However, Dr. Futter adds: “There are 23.5 million dairy cows in Europe, and approximately 265 million globally. Methane emissions from Baltic Sea clams are virtually irrelevant when compared to those from the dairy sector. Furthermore, the study results show that one tonne of dairy cows (about two cows) emit at least 500 times the methane emitted by one tonne of clams.” Dr. Jason Bailey, marine biologist and aquaculture specialist from East Regional Aquaculture Center (ERAC), expressed concern in extrapolating the results of the study and drawing conclusions to which the study was not designed to address. “While clams and mussels are related species, they are also clearly different species. In order to address concerns regarding mussels and methane production, one should begin by looking at mussels, not a species in the same Class of which there are 1000s of other species. Comparing clams living in sediment mud to mussels growing on ropes near the surface is an extreme extrapolation of the findings of the study and might be akin to comparing methane production in two species of mammals, say squirrels and humans!”

Dr. Futter agrees: “Based on the study, there is no reason to believe that mussels will produce the same amount of methane as clams. In fact, it is quite likely that mussels will produce less methane, possibly much less.”

SLU and ERAC are two of several organisations in the Baltic Sea region involved in the EU-financed project Baltic Blue Growth. The project consortium is implementing mussel farms as a nutrient reduction measure in 5 different countries around the Baltic Sea, and also studies industrial processes to use mussels as a feed ingredient.

 To read the article by Bonaglia et al., “Methane fluxes from coastal sediments are enhanced by macrofauna.” Scientific Reports 7, 13145 (2017), click here

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