Mussels have been under much discussion in the aquaculture world recently. First, the results of a recent study found them to have a very low carbon footprint compared to other protein sources, and second because scientists are warning that the increasing acidification of the world’s oceans could have a damaging effect on these mollusks.

The good news is that a recent report by the Scottish Aquaculture Research Forum, “Carbon Footprint of Scottish Suspended Mussels and Intertidal Oysters,” found that rope-grown mussels have a carbon footprint of just 0.25 kilograms carbon dioxide equivalents per kilograms of mussels harvested, or 0.6 kilograms carbon dioxide equivalents per kilogram of mussel meat.

Shellfish farmers hope that this will make mussels even more attractive to retailers, who are actively seeking to reduce the carbon impacts of products on their shelves.

The study also compared the cradle-to-gate carbon footprints of mussels with other seafood and meat products and concluded that mussels can justifiably be promoted as a low-carbon food.

Researchers took existing figures for other products and attempted to convert them into comparable kg CO2-eq/kg edible units and found that British beef weighed in at 19, British sheep at 18.8, pork at 8.6, and British poultry at 6.5.

The carbon footprint of Canadian salmon came in at 4.2 using figures produced by Pelletier and Tyedmers 2007, and organic salmon at 5.4.

Jonna Meyhoff Fry, the researcher, hopes that the results of the study will make a positive contribution to reducing the environmental impacts of shellfish production even further, and lead to recommendations for best practice. She found in particular that fuel use implicated in both the harvesting and depuration of shellfish was a major contributor to the overall carbon footprint and suggested that careful analysis of operational procedures could help to lower this still further.

The bad news for mussels (and other shellfish) is that increasing ocean acidification could affect the formation of shells in adults, juveniles and larvae, have implications on reproductive activity, and also affect the plankton that shellfish feed on.

The world’s shellfish industry relies on the ability of mollusks to grow in their natural environment without outside input. They are adapted to withstand limited variations in temperature and food availability, but a pH level between 7 and 9 is necessary for shellfish to survive.  However, early life-stages need a pH of 8.2 for successful growth and this has dropped by 0.1 percent over the past two hundred years as ocean acidity has increased by around 30 percent.

Scientists predict that the rate of change will accelerate in coming decades and by the end of the 21st century, the pH of the surface ocean is projected to be 0.4 – 0.5 pH units lower than today, leading to concerns about the overall effect on marine life. Laboratory experiments show a dramatic reduction in adult mussel shell formation at lower pH levels, although oysters seemed more able to tolerate the conditions.

Frances Hopkins of Plymouth Marine Laboratory explained that under normal circumstances, seawater maintains a balanced pH level but increasing growth of human activities that generate higher levels of carbon dioxide and contribute to ocean acidification, means that pH levels are decreasing. Such activity includes deforestation, burning of fossil fuels, cement production, discharge from industries, and runoffs from farms.

A 5-year GBP 12 million UK Ocean Acidification research program is looking at all the potential effects of ocean acidification and the likely social and economic impacts. Involving 150 scientists from 23 universities and research institutions, the project is investigating a wide range of commercially important fish and shellfish species. Full details can be found at www.oceanacidification.org.uk.

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