Reducing sea lettuce growth

08 June 2017

The Department for Infrastructure and the Department of the Environment are working on short and longer-term ways of reducing the annual build-up of sea lettuce.

Sea lettuce is 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

The Department of the Environment, Department for Infrastructure, and Société Jersiaise monitor and collect data throughout the year. This research provides valuable information about the growth of sea lettuce.

What is being done short term

The Department for Infrastructure moves the sea lettuce from the top part of the beach using a surf-rake machine. This keeps slipways, beach concessions and cafés clear.

Limitations

Sea lettuce can’t be moved when on top of stones.

The Department for Infrastructure doesn’t have the resources or remit to remove the seaweed from further down the beach.

An environmental licence is needed to move material on the beach. This licence gives strict conditions on how sea lettuce is removed.

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, or drive machinery, in these areas.

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.

Light deposits collected by the surf-rake machine can go to La Collette to be mixed with other composting material. There's no capacity there for large quantities and there would also be potential odour issues.

Current methods of removing sea lettuce from the beach mean it's contaminated with sand. This 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 suitable for depositing directly on to agricultural fields.

What is being done long term

The scientifically accepted long-term approach to reduce sea lettuce is to limit the nutrients coming into St Aubin's Bay. Land-based nitrates are reducing. Farmers are using less fertiliser and better techniques.

The Water Management Plan

The introduction of a Water Management Plan (note 4) will make sure nitrate levels in our waters continue to fall.

This plan involves working alongside farmers on the Action for Cleaner Water group to improve agricultural and horticultural practices and reduce fertiliser use. The plan also covers the building of a new £75m water treatment works which will improve the quality of treated waste flowing to St Aubin. This will be completed by 2022.

Data collection and monitoring

Officers at Environment and Infrastructure, and the Société Jersiaise collect data and analyse this throughout the year following strict European methodologies.

They sample the inshore beach area (the growth zone of green seaweed), assess how much and where the sea lettuce is (using four time-lapse cameras along the bay), and monitor the health and distribution of seagrass.

Environment's scientists assess the results before deciding if larger scale works are worth carrying out.

Scientific support

The States have worked with the following bodies, commissioning reports and data to make sure the approach is backed by scientific evidence and practice:

Jersey Sea Search (now Jersey Marine Conservation)
Société Jersiaise
Centre for Environment, Fisheries and Aquaculture Science (Cefas). A world leader in marine science and technology, which collects, manages and interprets data on the aquatic environment, biodiversity and fisheries
Ricardo (Cascade) Consulting
Ifremer (L'Institut Français de Recherche pour l'Exploitation de la Mer)
Ifremer website

Further details about sea lettuce growth in Jersey

Environmental Health monitoring shows no gas build up, as reported elsewhere in Europe.

There is no evidence that sea lettuce is disrupting St Aubin's Bay's ecosystem, including the important seagrass beds.

Bathing water in St Aubin's Bay is 'good' to 'excellent' quality (note 1).

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 (note 2).

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 (note 3).

Notes

Note 1: survey results from the EU Bathing Water Directive.
Note 2: since 2013 the Department of the Environment and Société Jersiaise have undertaken annual biological surveys of the seagrass beds in St Aubin’s, St Catherine’s and Grouville Bays.
Seagrass monitoring on the Jersey Coast website
Note 3: FEPA licence issued by the Department of the Environment.
Note 4: the catchment source approach and the Water Management Plan were recently reviewed by the Environment, Housing and Infrastructure Panel.