The environmental and economic benefits of bivalve aquaculture in the UK

Bivalves, a type of shellfish like mussels, oysters and clams, are more than just seafood; they are key players in keeping our water in good condition and supporting marine ecosystems. 

These shellfish help reduce eutrophication, a problem which happens when there are too many nutrients, like nitrogen and phosphorus, in the water. 

Nutrients are important building blocks of life and a natural part of aquatic ecosystems, but in excess, they can cause large algae blooms, which use up oxygen, harm fish and other aquatic life. 

Bivalves improve water quality by filter feeding, which means they pump water through their body, trapping and consuming small food particles and organisms, such as algae forming blooms. This helps balance nutrient levels and supports other marine life.

This ability is especially important in nutrient-rich areas, such as coastal zones and estuaries, where high levels of nutrients promote eutrophication. 

There, bivalves could work alongside traditional water improvement methods to manage these nutrient levels. 

Besides their environmental benefits, bivalves are also a great source of nutrition. 

They are rich in protein and other nutrients, making them a valuable part of the UK's natural resources. 

In 2019, the UK produced 16,000 tonnes of bivalves, worth nearly £22 million.

The UK has an opportunity to use bivalves for environmental and economic gains. 

This is why we conducted our own research into water quality improvement services provided by commercially important bivalve species.

Our research on ecosystem services of bivalves

Together with Agri-Food and Biosciences Institute (AFBI), and supported by Longline Environment Ltd and the Fishmonger’s Company, we began a study to answer two key questions:

• What is the capacity of the UK bivalve sector to remove nitrogen naturally?
  What are the potential financial savings from this nitrogen removal?
• To answer these questions, we used two methods to provide both, conservative and not-so-conservative estimates.

Firstly, we used the results of elemental analysis, is a technique that measures the number of specific elements, like nitrogen and carbon, in a substance. This analysis was done as part of the European project GAIN, a research initiative by our partners at AFBI. It provided us with information on the nitrogen and carbon content of blue mussels, Pacific oysters, Native oysters, and Manila clams. It is important to consider different species of bivalves that are grown around the UK. Each species has a different elemental composition of its tissue and shell, and different farming methods can also affect nitrogen content.

Second, we used the Farm Aquaculture Resource Management (FARM) model, provided by Longline Environment Ltd. This advanced and widely used system combines information on different shellfish species, their environment, and farming practices to estimate how many bivalves can be harvested and how much nitrogen they can remove from the water.

We then scaled up the results of both analyses to the national level using bivalve production data from 2019. This information was supplied by the Centre for Environment, Fisheries and Aquaculture Science (CEFAS).

Highlights from our ecosystem services work

Based on the 2019 bivalve production data, we estimated the UK bivalve industry removed between 126 and 362 tonnes of nitrogen. 

Blue mussels were the main contributors and removed over 92% of the total nitrogen removed by shellfish.  

Scotland and England were the top regions for nitrogen removal, reflecting the high production of bivalves in these areas. As bivalve farming grows, the potential for even greater nitrogen removal in the future. 

This nitrogen removal adds to the other benefits bivalves provide, such as supporting marine life and contributing to the food industry.

We also compared the amount of nitrogen removed by bivalves to the amount of nitrogen entering UK waters from various sources. This comparison showed that Northern Ireland and Wales removed the highest proportion of their nitrogen loads through bivalves, with averages of 0.25% and 0.24% respectively. 

In England and Scotland, bivalve harvests could offset a significant portion of industrial nitrogen sources. These results translate to tangible water quality improvements.

Financially, nitrogen removal by bivalves offers substantial savings. 

We calculated the value of these potential savings by comparing the cost of bivalve nitrogen removal to other methods. These can be measures such as chemical and manual wastewater treatment or stormwater control. Similar avoided cost methods have been successfully applied before for oysters in Solent, Dundrum Bay, United States, and mussels of the Baltic Sea.

In this study we first applied data from a water treatment facility where the cost of nitrogen removal was around £58 thousand per tonne of nitrogen. 

Based on our estimates, the total savings across the UK could be between £7 million and £21 million a year, depending on which of the nitrogen removal scenarios we look at.

However, bivalve nitrogen control abilities can be particularly important in areas at risk from eutrophication, and hard-to-manage nitrogen levels that require additional management efforts.

In these areas, bivalves could bring an additional £1.1 to £3.2 million in savings when compared to the costs of effective catchment management.

We also examined research from the Solent area, conducted by the University of Portsmouth. Their study found that Native oysters have an annual value of £37.44 million for nitrogen removal and £6.77 million for phosphorus removal. They also estimated that reducing one tonne of nitrogen through alternative methods costs about £295,000. Applying this figure to our work suggests that using bivalves could lead to national savings ranging from £37 million to £106 million.

Another aspect are the costs of damage caused by too much nitrogen, such as lower property values near water, reduced commercial use of water bodies, and impacts on tourism. These costs for England and Wales have been estimated at £82.52 million to £125.75 million annually.

While these financial estimates vary, and there are many aspects to consider, they show significant potential savings in managing nitrogen with bivalves. However, there is a need to perform these studies on a regional or farm scale to provide more precise estimates.

To put our findings into perspective, we can look at similar research from around the world. Estimates from various locations also highlight the potential of bivalves to provide substantial financial benefits:

• Studies in Great Bay Piscataqua found that ouster nitrogen removal was valued at between £82,522 and £318,299;
• In Chesapeake Bay the annual value of nitrogen removal by oysters ranged from £439,920 to £9.82 million;
• In Greenwich Bay, the value of removing nitrogen was estimated between £129 to £325 per kilogram.
• In Long Island Sound, shellfish reefs can remove 1.3% of the nutrients entering the water, with avoided costs ranging between £6.68 million and £180 million annually.
• In Denmark's Limfjorden, mussel farming has provided savings of £1.34 million to £1.62 million. 

This places our findings in line with international research, emphasizing the broad and impactful role bivalves play in nutrient management worldwide.

Embracing Sustainable Solutions

Investing in bivalve aquaculture presents economic incentives and encourages continued research. 

However, the benefits go beyond just financial incentives; it is about embracing sustainable solutions and expanding natural processes in our seas. 

Globally, there is growing support for including bivalves in nutrient management plans, with ongoing research highlighting their environmental and economic benefits. The UK, with its extensive coastline and marine resources, is well-positioned to explore and expand this approach as well. 

Even though overall bivalve production has declined in the recent years, the UK shellfish industry was estimated to remove between 126 to 362 tonnes of nitrogen in 2019.

Mussels and oysters are particularly effective in this regard due to their higher nitrogen content and substantial production. 

Importantly, these bivalves remain safe to consume, providing a nutritious food source.

Bivalve aquaculture can improve water quality and offers potential cost savings of £7 to £21 million annually (compared to traditional chemical and mechanical methods). 

The capacity for nitrogen removal is closely tied to the size of the industry. Increasing future bivalve production will lead to even better nitrogen removal.

Find out more or get in touch

Ecosystem Services of Commercially Important Bivalves in the UK: Nutrient removal services - full report.

Report detailing the research on bivalve aquaculture's role in improving water quality in the UK, conducted in partnership with Agri-Food and Biosciences Institute (AFBI). 

This study outlines how bivalve farming aids in nutrient removal and supports sustainable aquaculture.

To download the study, please follow the link below:

For more information on this project, please contact Konstancja Woźniacka: