Bay of St Catherine seagrass protection initiative

The Bay of St Catherine supports a wealth of marine life; one of significant importance is the seagrass beds that have established in the area and reported to be the largest site around Jersey’s coastline.

Seagrass, along with being a vital nursery, provides shelter for marine fauna and at low water important feeding grounds for wildfowl and other birds. It is also recognised for its blue carbon, calculated to absorb carbon 35 times more than tropical rainforests.

map of St Catherine's Bay

Studies have highlighted that traditional mooring systems and anchoring cause significant damage to the seagrass and erosion to the seabed by the mooring chain, damaging the benthic ecosystems within the vicinity.

Satellite imagery taken in July 2021, clearly indicates areas of erosion around moorings in the seagrass beds. The average area of damage caused by a mooring is 100m2 and the largest area identified is 350m2 (based on 2021 aerial image).

aerial photo of damage to seabed at St Catherine

Our Mission

Our mission is to ensure that we are protecting this special and biodiverse rich habitat allowing the seagrass meadow to flourish, not just for the here and now, but for future generations.

Project goals

The project goals are to ensure there is mutually beneficial management of the area through consistent and adaptive administration of moorings within the deep-water site and to afford protection for the marine environment encapsulated within this area through the following methods:

  1. Ensure all moorings are identified and accounted for
  2. Gradually reduce the overall number of moorings within the deep-water site
  3. Establish a no-anchoring zone and visitor moorings where possible
  4. Remove any unused moorings
  5. Protect the seagrass beds as a valuable habitat for many marine ecosystems and for its recognised ‘blue carbon’ status.

A working group has been established consisting of the following:

Collectively working together with users of the bay to protect this valuable area.

Jersey’s hidden seagrass treasures – Blue Marine Foundation

Blue Carbon Resources: An Assessment of Jersey’s Territorial Seas (

Progress Updates

Tuesday 10th October 2022

Mooring Trials

In house teams have made up some moorings based on designs from workshops involving stakeholders and the working group.

Ports of Jersey In-house Designed Moorings

The moorings will be deployed on the next suitable tide and monitored to see how they interact with the seabed.


Monday 4th July 2022

Survey work

The initial stages of this work involve a study being undertaken by Jersey Marine Conservation on areas where Ports of Jersey have been able to remove unused moorings to establish the extent of the damaged caused and then the progress of the seagrass re-establishing within these areas.

Emily Dow, Science and Education Officer for Jersey Marine Conservation (JMC) updates on the progress of their study:

“Despite challenging diving conditions JMC have completed initial dive surveys across sites where the moorings have been decommissioned and removed by Ports of Jersey. Data has been gathered on the size of the damaged seagrass areas, density of the surrounding seagrass beds, including average leaf lengths and leaf numbers per shoot. The regrowth rate in these areas will be monitored by dive surveys and supported by aerial footage and underwater towed videos. This will demonstrate the rate of seagrass recovery we can expect to see when a mooring chain is not impacting the seabed.

As part of the dive survey work, sediment samples within the area close to the breakwater will be analysed. Sediment analysis will provide a direct comparison on the shallow seabed carbon storage, sediment quality and infaunal biodiversity between the damaged areas and surrounding dense seagrass meadow. This analysis will form part of an MSc dissertation project undertaken by a student from the Jersey International Centre of Advanced Studies (JICAS).”

Mooring Management

The next stages of the project are to look at the management of the moorings which will commence this week with the help of the users of the bay and we will also be trialling different mooring designs to study their impact on the seabed.

  • If your mooring is already registered with the Harbour Authority, please follow the link to the form to update your details.
  • If you are yet to register your mooring with the Harbour Authority, please follow the link to the Notice for more information