Blackwater and Colne Estuaries

The Native Oyster

The Blackwater, Crouch, Roach and Colne Estuaries contain the most important area in the South-East of England for the Native Oyster (Ostrea edulis) and the extensive oyster bed habitat that they create, made up of the oysters themselves as well as their dead shells.

Considered keystone species and ‘ecosystem engineers’, oysters create habitat for other species such as sea urchins by providing a solid surface on which to settle on, whilst providing protection and nursery grounds for small fish and other species. These habitats have been found to support a higher biodiversity of invertebrates and fish than surrounding unstructured habitats. Oysters also provide optimal conditions for other species by stabilizing shorelines and improving water quality through filtering excess nutrients from large quantities of water.

Once a common species around the Essex coast, the Native Oyster has declined by 95% in the last 200 years from historic over-exploitation, with recovery hampered by habitat loss, disease, pollution and competition with invasive non-native species (INNS), making the remaining oyster beds the most threatened marine habitat in Europe.

Such a severe decline in the oyster population means that the natural replenishment of their native grounds is unlikely. With their recovery so limited without human intervention, the Essex Native Oyster Restoration Initiative (ENORI) was established with the aim of recovering Native Oysters in the Essex estuaries, creating a self-sustaining population which provide ecosystem services, sustainable fisheries and increased biodiversity whilst recognising their cultural importance. The coalition, which is chaired by the Zoological Society of London (ZSL) is made up of oystermen, NGOs (including Essex Wildlife Trust), universities and government bodies.

Marine Conservation Zone (MCZ) designation

In 2013 the Blackwater, Crouch, Roach and Colne Estuaries were recognized for their importance to the Native Oyster and Native Oyster beds, when a 284m2 area was designated as a Marine Conservation Zone (MCZ), making it the UK’s largest inshore MCZ. The objectives of the designation include the recovery of the Native Oyster species and the Native Oyster bed habitat it creates to ‘favourable’ condition.

The designation builds on existing protected sites such as the Essex Estuaries Special Area of Conservation (SAC) and Sites of Special Scientific Interest (SSSI) by offering protection to features such as the native oyster which are not already protected through these existing designations.

In addition the MCZ includes an area of intertidal mixed sediments and extends the existing protection of the internationally important Clacton Cliffs and Foreshore into the subtidal zone. One of the best ice age sites in the UK, this geological feature of the MCZ contains an abundance of fossil remains.

Blackwater Restoration Box

Within the MCZ a 2km2 (200ha) voluntary no-take conservation area has been created specifically for the purpose of restoring Native Oyster bed habitat. Adding crushed waste shells and stones to the muddy estuary floor improves the seabed for oysters by providing a hard surface for them to settle and grow upon. This process is colloquially called ‘laying the cultch’ and is the first step in the restoration process. ENORI have established a sustainable supply chain of Mersea bred oyster shells from Borough Market and West Mersea.

Once ’laying the cultch’ is complete adult female or ‘Mother Oysters’ are translocated and laid on the newly improved seabed to spawn, initiating the first stages of the Native Oyster’s life cycle. Juvenile oyster spat will in turn settle and grow on the harder, improved substrate.

ENORI is closely monitoring the oyster population in the MCZ and will enable low level, sustainable harvesting if the population proves resilient enough, outlined in a fisheries management plan. The management plan was formalised in 2018 under the Native Oyster Fishery Flexible Byelaw, closing the restoration box to oysterdredging and harvesting activities for 10 years, after which it will be reviewed by an expert group.

Saving an Essex icon

Intrinsically linked to the county’s identity oyster farming has been part of the Essex landscape and diet for thousands of years, with evidence of stone-age hunter gatherers harvesting oysters. Oyster farming has been recorded on Mersea Island during the Roman era, forming a staple part of their diet. Today, the Native Oyster remains at the heart of the communities of the Essex estuaries, with the ENORI project as much about preserving a threatened heritage as it is about preserving a threatened species.



Blackwater and Colne Estuaries

WFD water body status


Project type

Habitat restoration

Benefiting species and/or habitats

Native Oyster (Ostrea edulis)

Total area covered by project


Project lead

Essex Native Oyster Restoration Initiative (ENORI)

Contact for more information

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Project start


Website key stakeholders:

Environment Agency logo      Essex Wildlife Trust logo           ESWT Logo 70

Design by LTD Design Consultants and build by Garganey Consulting based on an original concept by Herts and Middlesex Wildlife Trust