The Solent Forum

Working in partnership for the future

Species and Habitats


The Solent is a huge single estuarine system which contains in excess of 9,000ha of intertidal sediment, and includes over 6,000ha of mudflats, 7,000 ha of sandflats, 400ha of ancient saltmarsh and nearly 1,800 ha of Spartina marsh.  The mudflats are rich in invertebrates and are consequently important feeding grounds for waterfowl and waders. Specific habitats include grazing marsh, vegetated shingle, sea cliffs, saltmarshes, mudflats, sand flats, rocky shores, lagoons and a variety of types of sea-bed. This includes unusual examples of natural gradations from maritime to coastal and marine habitats, that have been lost from other areas of the south coast.  It is located at a transition between different biogeographic realms; therefore, many species are at the limits of their natural ranges.

Much of the Solent is designated as a Special Area of Conservation (SAC) and Special Protection Areas (SPA). The  Solent Maritime Special Area of Conservation has been designated for its abundant sandflats, mudflats, Atlantic salt meadows, coastal lagoons and estuaries. These important habitats in turn support a wide range of flora and fauna including common eelgrass, spiny seahorses, Desmoulin's whorl snail, oysters, skates, rays and a variety of wading birds and seabirds. The Solent is also home to three Special protection areas (SPAs) and three Ramsar sites which have largely been designated for their internationally important wetlands to help protect important populations of Common, Sandwich and Little Terns.

Currently much of the Solent Maritime SAC is in unfavourable condition in part due to poor water quality standards. Important mudflat and sandflat habitats which support nationally rare seagrass beds are exhibiting a declining condition. This is due to elevated nutrient levels, causing beds to reduce in extent, distribution and biomass. Condition assessments for Solent SPAs and Ramsar sites are yet to be released but initial Wetland survey reports show a number of important bird features to be in decline.

Although the Solent’s habitats, such as mudflats, saltmarshes and seagrass beds, are affected by high nutrient levels they also provide valuable nutrient cycling services that help improve water quality. They also provide many other ecosystem services, including carbon sequestration, fishery provisions and coastal protection. Restoring and maintaining these valuable habitats is part of the UK government’s 25-year environment plan to “secure clean, healthy, productive and biologically diverse seas and oceans” and to create climate resilience through nature-based solutions.

Policy and Governance

The UK Marine Strategy Framework provides a framework for delivering marine policy across the UK, from coastal waters to the seabed of the continental shelf. It is set out in three stages in order to achieve good environmental status for our seas and focusses on biodiversity; non-indigenous species; commercial fish; food webs; eutrophication; sea-floor integrity; hydrographical conditions; contaminants; contaminants in seafood; marine litter and underwater noise.

The EU Water Framework Directive was introduced to address pollution from urban sources and agriculture from entering our water ways. To manage this a river basin management plan was established to help achieve good ecological and chemical status for all waters and expand protected waters to include surface water and groundwaters.

The Environment Act, introduced in 2021, sets out new targets to aid natural recovery with focussing on four key areas: air quality, biodiversity, water and waste. Ambitions to reverse the decline of species abundance are also included in this act which comes under the UK Government's 25-year environment plan.

There are 9 management catchments that make up the South East River Basin District. In order to support economic growth within the South East, The South East River Basin Management Plans stipulates that large scale projects occurring within river catchment areas must take account of the basin’s environmental objectives and potential benefits and impacts of the project must be considered.

Southern Water are implementing long-term drainage and wastewater management plans (DWMPs) and are investing in wastewater and drainage systems that are suitable for future climate and population changes and ensure sustainable drainage infrastructure. So far DWMPs have been developed for the Test and Itchen catchment, the New Forest, Isle of Wight and the East Hampshire catchment.

You can explore river basin districts across the UK using the Catchment Data Explorer, where you can find management catchments in your area.

How Does Water Quality Impact Habitats and Species?

Coastal waters can be become polluted from man-made chemicals, such as polychlorinated biphenyls (PCBs), or nutrient polluted from fertiliser and sewage runoff in a process known as eutrophication. The use of toxic PCBs has been illegal since 1987 but their longevity still makes them a problem today, particularly due to their bio-accumulative properties. This means animals at the top of the food chain are most affected, like seabirds and marine mammals. Most commonly exposure to excessive PCBs can cause reproduction problems, loss in motor control and cancer. Eutrophication events occur when there is excess nitrate and phosphate in the water column, this stimulates macroalgae blooms which smoothers any existing life leading to microbial decay which causes a loss of oxygen and ultimately a loss in biodiversity.

Maintaining good water quality standards not only helps protect characteristic species but it helps preserve the intrinsic balance within our ecosystems, supporting local fisheries, carbon capture and coastal recreation.

See the Solent Forum’s pages on marine litter, nutrients and microplastics for more information.

Solent Context and Issues

Eutrophication poses the greatest threat to the Solent where much of Southampton, Portsmouth and the Isle of Wight are designated as nitrate vulnerable zones (NVZ). Over the last 20 years nitrate reduction efforts, including permit changes to sewage treatment works and voluntary measures like catchment sensitive farming and environmental stewardship schemes have decreased the levels of nitrate entering the Solent. Environmental land management schemes have also aided water quality improvements by incentivising sustainable farming practices and local nature and landscape recovery.  Despite active efforts to reduce nitrate concentrations previous  condition assessments for special protection areas and Ramsar sites in the Solent, Southampton Water, Portsmouth, Chichester and Langstone Harbour have shown that 81% of these areas remain in unfavourable condition. Wetland bird surveys have also noted a number of declining bird features which may be linked to increased nutrient loading.

Per unit area saltmarsh beds are the most effective habitats at removing excess nitrate from the water column, these habitats are found in many of the smaller estuaries around the Solent, such as the Yar Estuary and the Hamble Estuary. Seagrass beds and native oyster beds (Ostrea edulis), also contribute to nitrate and phosphate removal, but due to their small extent across the Solent the overall nutrient flux from these habitats is small.

Solent Initiatives

Solent Oyster Restoration Project

Although oysters are sensitive to eutrophication events, oyster beds contribute towards nutrient cycling and removal of organic matter through filter feeding and provide a nursery habitat for commercially viable fish stocks. The Blue Marine Foundation is working with partners to restore native oyster beds to the Solent and develop a sustainable fishery. Oyster reefs at Langstone Harbour are already fully established and will hatch one million oyster a year, repopulating the Solent. This restoration project is of high priority both nationally and globally and will contribute towards the UK’s biodiversity action plan. 

Solent Nutrient Market Pilot

The Solent Nutrient Market Pilot is currently testing an online nutrient trading platform which aims to help landowners deliver nature-based solutions to reduce nitrate and phosphate pollution and support new developments in delivering nutrient neutrality.

Solent Seagrass Restoration

Currently there are three schemes which aim to restore seagrass beds in the Solent:

  1. The Solent Seagrass Restoration project by the Hampshire and Isle of Wight wildlife Trust and partners.
  2.  The Solent Ocean Rescue project involving WWF, Project Seagrass and Swansea University.
  3. The LIFE recreation ReMEDIES project.

These projects are currently underway and aim to restore and identify sites for seagrass restoration. Seagrass contributes towards nutrient cycling helping to improve water quality standards in the Solent as it recovers to historical distribution.

Algal Mat Removal - RaNTrans

This is an Interreg funded project that works to physically remove algal mats and reduce the negative impacts caused by eutrophication. It is being tested in the Solent, Langstone and Poole Harbour and other areas around the UK and Europe. A predictive and interactive web-based model will be produced to help tackle algal mats due to eutrophication in the future. 

ChaPron – Chichester Harbour Protection and Recovery of Nature

Based in Chichester Harbour this initiative is a long-term plan to help protect, enhance and drive nature recovery within the Harbour. The work includes coastal resilience and saltmarsh restoration, seagrass distribution, catchment sensitive farming, reduce bird disturbance, native oyster restoration and community engagement.


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