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Information and public services for the Island of Jersey

L'înformâtion et les sèrvices publyis pouor I'Île dé Jèrri

Causes of sea lettuce

13 August 2015

​The growth of sea lettuce occurs in shallow sandy bays throughout the world in the warmer months. It is a global issue – not one which is unique to Jersey. Nearby places along the south coast of England and the adjacent French coast also experience periodic blooms of the weed.

Sea lettuce is not a recent phenomenon and has occurred in St Aubin’s Bay, to varying degrees, for decades. Sea lettuce needs a specific mix of warm sea temperatures, light and nutrients (nitrates) in order to grow and although work is continuing to find ways to limit its growth, sea lettuce will still appear in the bay.

25 per cent reduction

The Department of the Environment, the Société Jersiaise and the Transport and Technical Services Department (the latter as part of the planned replacement of the sewage treatment works) carry out regular monitoring of water quality and the level of sea lettuce in St Aubin’s Bay. Monitoring the water quality in the bay is helping to assess how controlling nitrates at source might be able to limit sea lettuce growth and also helps to plan the beach cleaning. The information also enables Jersey to compare the quality of its water to other places in Europe.

Land-based sources of nitrogen are important inputs to the bay and the Department of the Environment is working with the Transport and Technical Services Department and farmers and other land managers to control nutrient inputs at source. Work with farmers has made good progress and the level of nitrates in island streams has reduced by more than 25 per cent since 1998.

Water Plan for 2016

There is still much to be done and a Nitrate Working Group (involving farming representatives, the Department of the Environment, Economic Development, Jersey Water and officers from the Health and Social Services Department) has recently produced recommendations that will inform a wider Water Plan. In addition to nitrate linked to farming, these measures will help to reduce other potential sources of nitrate (including from private drainage systems and leisure amenity grassland etc.). The Water Plan, which will be published in 2016, will identify and seek to address the priority water quality issues on the island in a proportionate way. 

As a priority this work will continue to focus on getting nitrate levels in streams and groundwater (Jersey Water’s public supply and private borehole and well water) to below the EU and Island recommended limit of 50 milligrams per litre.

Surrounding waters

Reducing nitrates in the streams that flow into St Aubin’s Bay and the inflow into the Sewage Treatment Works will also go some way to help reduce the nutrients available for sea lettuce growth in the bay. It will, however, not eradicate sea lettuce completely, as the background levels of nitrate are also somewhat heightened in the Island’s offshore surrounding waters and the characteristics of St Aubin’s Bay and our climate make the conditions good for the growth of sea lettuce during the summer months.

Measures to move sea lettuce

The Transport and technical Services Department carries out beach cleaning on behalf of Visit Jersey. First priority beaches are West Park, Bel Royal, the Gunsite slip/cafe, and La Haule slip/café. Second priority beaches are the First Tower café area, Millbrook, and the 'Sugar Basin' slip. 

During the summer season the department endeavours to keep the top part of the beach, where people sit and play, clear of litter and seaweed/sea lettuce, especially near the slipways, beach concessions and cafés. It uses a specialist machine which is not suitable for use when there are many beach users around so removal is limited to early mornings – and then only when the tide is low enough. In some areas, seaweed collection is restricted by stones on the beach.

This machine normally works on alternate days, west of the Island beaches one day, east the next, but with a close eye kept on West Park because of the Jubilee Marine Lake. Operations are governed by the tide height and tide times so there are days when access to the beaches is limited.

Composting weed

TTS can compost small volumes of weed as it is an organic material, however the limited space available at La Collette (which conforms to leachate prevention requirements) and the high cost, makes it unrealistic and unviable for large quantities of weed.

When large volumes of sea lettuce have to be moved, the only realistic option is to take it back to the low water mark. Sometimes, the tidal and weather conditions can mean that the sea lettuce will return to beaches very quickly when moved offshore. The tides, wind and weather also mean that the sea lettuce can and does move on a daily basis.

Years ago, it was taken inland to dumps such as Crabbé, however this created more environmental pollution problems and odour complaints from neighbours, and is not an option now.
TTS has investigated the possibility of using a towed barge to dump the weed out to sea, but this would cost an estimated additional £100,000 per season and would result in a barge being beached in the middle of St Aubin's Bay all summer.

Ecologically sensitive area

Sea lettuce deposits further down the beach at St Aubin’s Bay are also lying in an ecologically sensitive area, on top of sea grass beds - a protected marine growth, and can’t be easily moved without causing damage. TTS is prohibited from removing seaweed in these areas or driving machinery over them.

TTS wouldn’t seek to move deposits this far down the beach as it doesn’t have the resources or remit to do so and the next incoming tide would create the same problem the following day.

The department will continue to keep the top of the priority beaches as clean as it can, as regularly as possible, and only remove heavier deposits of sea lettuce from the same areas if they become a public nuisance, and then only after the top of a spring tide so that the next high tide doesn't undo this work.





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