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Reducing sea lettuce growth

The scientifically-accepted long-term approach to reduce sea lettuce is to limit the nutrients coming into St Aubin’s Bay

​Sea lettuce is a type of seaweed found along coastlines around the world. It grows in St Aubin's Bay because conditions are shallow, enclosed and relatively warm.  Its growth is increased by:

  • nutrients from outside the bay
  • run-off from streams that contain fertiliser
  • treated waste water from the water treatment works

Reducing sea lettuce growth

The Department of the Environment, Department for Infrastructure, and Société Jersiaise work together to monitor and collect data throughout the year.  The data collection and analysis follows strict European practice. Officers also work with recognised scientific experts and agencies to find solutions based on solid research and international best practice.

The Department for Infrastructure and the Department of the Environment, with help from recognised scientific experts and agencies (including those from similarly affected areas of France), are working together on short and longer-term ways of reducing the annual build-up of sea lettuce.

Short-term, the focus is to reduce the impact of the growth on the bay. Longer-term, the aim is to limit the growth of the sea lettuce as much as possible by reducing nitrates from the land and Jersey’s water treatment works.Both departments are working to reduce the annual build up of sea lettuce. 

States officers have carried out extensive data collection, monitoring and research to learn more about the growth, and various ways of tackling it so that solutions proposed are based on solid research and international best practice, and are effective and value for money.

As with all departmental work, any proposals are challenged and fully investigated to assess their scientific merit and best practice.

Short-term actions

To keep the top part of the beach clear, the Department for Infrastructure moves the sea lettuce at regular intervals throughout the summer, especially near:

  • slipways
  • beach concessions
  • cafes

Tide times and weather conditions dictate when and where the sea lettuce is moved and it cannot be moved from on top of stones.
The department uses a ‘Surf-Rake’ to remove light amounts at times when there are few beach users around so removal is usually limited to early mornings – and then only when tides permit. Larger vehicles are used to move more substantial deposits.
The department doesn’t have the resources or remit to remove the seaweed further down the beach. It also has to take the following into account:

Environmental restrictions

  • the Department for Infrastructure needs an environmental license to move material on the beach. This license places restrictions and conditions on how it removes sea lettuce
  • clearance is only effective for a few days after a spring tide when the seaweed would otherwise be stranded at the high level of the beach
  • sea lettuce deposits further down the beach at St Aubin’s Bay are lying in an ecologically sensitive area, on top of seagrass, and can’t be easily moved without causing damage. The Department for Infrastructure is not allowed to remove seaweed in these areas or drive machinery over them
  • removing the seaweed from stony parts of the beach, in particular, at the First Tower part of the beach is difficult using machinery and poses the risk of also removing the stones

Other limitations

  • light deposits collected by the Department for Infrastructure Surf-Rake machine can go to La Collette to be mixed with other composting material, but there’s no capacity there for large quantities and there would be potential odour issues.
  • current methods of removing sea lettuce from the beach mean it’s contaminated with sand and so can’t be disposed of at the Energy from Waste Plant due to potential sand damage to the plant
  • sea lettuce has a high salt content so it’s not considered suitable for depositing directly on to agricultural fields.

Longer-term measures

The scientifically-accepted long-term approach to reducing sea lettuce in St Aubin’s Bay is to limit the nutrients coming into the bay. It is not possible to control the nutrients from outside the bay, but it is possible to further reduce nutrients, mainly nitrates, coming from land-based sources. Controlling on-island sources of nitrate will help limit its growth, but it is highly unlikely that these actions will eradicate it completely.

The following measures, set out in the States-approved Water Management Plan  will ensure nitrate levels in our waters continue to fall

  • close working with farmers, through the Action for Cleaner Water group, to improve agricltural and horticultural practices and reduce fertiliser use
  • a new waste water treatment works, due to be completed by 2022, will improve the quality of treated waste flowing to St Aubin

Facts about sea lettuce in Jersey

  • sea lettuce grows across the globe, not just in Jersey
  • environmental Health monitoring shows no gas build up, as reported elsewhere in Europe.
  • bathing water in St Aubin’s Bay is ‘good’ to ‘excellent’ quality
  • sea lettuce growth occurs in St Aubin’s Bay because it is shallow, enclosed and relatively warm. Its growth is also dependant on nutrients from outside St Aubin’s Bay and is also affected by sources including land run-off from streams that contain fertilisers and treated waste water from our water treatment works
  • the long-term target is to limit the growth of sea lettuce as much as we can by reducing nitrates from the land and the treatment works. We can’t stop nutrients coming in from the surrounding sea
  • land-based nitrates are reducing. Farmers are using less fertiliser and better techniques. This is co-ordinated through the joint Action for Cleaner Water Group and the new Water Management Plan
  • the States is investing £75m in a new water treatment works to be completed in 2022. This will help reduce sea lettuce growth
  • the Department for the Environment and the Department for Infrastructure are carrying out extensive research on sea lettuce, St Aubin Bay’s ecosystem and the ecologically important seagrass beds (Zostera noltii), involving international experts
  • the Department for Infrastructure moves the sea lettuce at regular points throughout the summer when it builds up. The movement is controlled by a licence to protect the ecosystem of the bay, including the sea grass
  • tide times and weather conditions determine when and where the sea lettuce is moved
  • the lower part of the beach at St Aubin’s Bay is an important ecological area and sea lettuce can’t be moved from here without causing damage
  • there is no evidence that sea lettuce is disrupting St Aubin’s Bay’s ecosystem, including the important seagrass beds

Data collection and scientific support

Data collection and monitoring

Officers at Environment and Infrastructure, and the Société Jersiaise, collect data throughout the year. Data collection and analysis follow strict European methodologies. Further studies involve sampling of the inshore beach area (the growth zone of green seaweed), assessing how much and where the sea lettuce is (using four time-lapse cameras along the bay) and monitoring of the health and distribution of seagrass.

Scientific support

The States has worked with the following bodies, commissioning reports and data in its efforts to ensure the approach for sea lettuce removal is backed by scientific evidence and practice.

  • Jersey Marine Conservation (previously Jersey SeaSearch)
  • Societe Jersiaise
  • Centre for Environment, Fisheries and Aquaculture Science (Cefas) - a world leader in marne science and technology.  It collects, manages and interprets data on the aquatic environment, biodiversity and fisheries
  • Ricardo (Cascade) Consulting
  • Infremer (L'Institut Francais de Recherche pour l'Exploitation de la Mer)


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