SoNaRR 2025: Marine

The marine ecosystem includes the intertidal and subtidal inshore areas. The intertidal is the area between the high water mark and low water that is inundated with seawater at some stages of the tidal cycle. The subtidal is the area that is permanently immersed in seawater.

Key messages

• Wales has a rich and diverse marine ecosystem which can provide many important services for people and the economy, including food, energy, blue carbon and recreation. If appropriately managed, this could generate revenue to invest in local ecosystem resilience, markets and communities.
• Around half of the species and habitats assessed in Welsh marine protected areas (MPAs) are in unfavourable condition. There are multiple causes; one of the main causes is water pollution. The condition of habitats outside MPAs is thought to be an equally mixed picture.
• Climate change is leading to increasing pressures affecting Welsh marine ecosystems, including sea level rise and increased temperatures. Expansion of offshore renewable energy to meet net zero targets needs careful management to meet the requirements of both the climate and nature emergencies.
• Effective marine management to reduce pressures, actions to restore habitats, and land based management to tackle multiple sources of pollution, are required to improve resilience of marine ecosystems.
• Addressing many of the known pressures requires a strategic and multi-faceted approach, for example through marine planning, building the evidence base, and driving behaviour change through engaging people with the sea.
  
  

Assessment of SMNR

This marine assessment is one of eight ecosystem and three natural resource assessments that inform the overall SoNaRR2025 report. It builds on the findings of SoNaRR2020, drawing together updated evidence from subject experts, national datasets, and collaborative projects such as the Marine Climate Change Impacts Partnership. This assessment is closely linked to the Coastal Margins ecosystem assessment and Water resource assessment.

The assessment is structured around four interlinked aims that guide Wales’s progress toward the sustainable management of natural resources (SMNR), helping to communicate the relationship between the environment, well-being, and the economy.

Aim 1: Stocks of natural resources are safeguarded and enhanced

Welsh seas contain a rich variety of natural resources. Populations and habitats show mixed trends, and key pressures affecting their condition and extent include climate change, disease, water pollution, invasive species and marine activities. Climate change is a growing threat with increasing sea temperatures, accelerating sea level rise and increasing ocean acidification. Climate induced changes in species distributions and survival, and the extent and condition of coastal habitats are already being observed.

Water pollution remains a persistent issue. Excess levels of nutrients in estuaries (point and diffuse, e.g. from agriculture), are impacting condition, and contaminants like mercury and PCBs are still present at harmful levels in some areas. Marine litter, especially plastics, remains widespread despite some short-term improvements. Although there is low confidence in the data available for more recent trends of marine Invasive Non-Native Species (INNS), they continue to impact biodiversity and marine industries. Anthropogenic underwater noise is widespread and likely to increase with expanding marine development. Highly Pathogenic Avian Influenza has led to sharp declines in internationally important seabird populations since 2021.

Funding mechanisms are being developed to support delivery of actions to safeguard and enhance species and habitats (e.g. Marine Fund Cymru), and there is a growing emphasis on developing and communicating evidence to help target effort to support positive outcomes. Going forwards, SMNR and strategic planning need to be climate-smart, taking account of predicted changes and adapting approaches to meet the implications of a changing climate.

Aim 2: Ecosystems are Resilient to Expected and Unforeseen Change

Marine ecosystem resilience is assessed through diversity, extent, condition, and connectivity. There is a mixed picture for diversity in Welsh seas. Declines have been noted in some specific areas, such as the intertidal habitats in Milford Haven and the horse mussel beds in Pen Llŷn A’r Sarnau Special Area of Conversation, although diversity of many habitats remains stable. Marine habitat extent also shows a mixed picture in long and short term trends. For intertidal habitats, the long term trend is a decrease in extent but the short term trend is more variable. The picture for subtidal habitats is also mixed although there are known decreases in extent of maerl beds. Over the long-term, condition of habitats has been deteriorating in the intertidal zone linked to pressures including overgrazing, water pollution, coastal development and activities like bait digging. Condition of subtidal habitats show mixed trends. Connectivity across marine habitats is generally high and stable.

Actions to enhance resilience of marine ecosystems are gaining momentum, this includes recovery of habitats and species through the removal of pressures and active restoration. Work is also progressing to fill evidence gaps to understand the factors which are impacting resilience, and to identify which areas are most suitable for recovery and restoration to target action and deliver positive outcomes.

Aim 3: Healthy Places for people, protected from environmental risk

Marine ecosystems support human health by regulating climate, protecting coasts, and purifying water. Crucially, Welsh marine habitats store over 113 million tonnes of carbon, comparable to Welsh forests, and sequester thousands of tonnes annually. Seagrass and kelp help reduce coastal erosion and flood risk. Bathing water quality is high, with 94% of designated sites rated Excellent or Good in 2025.

Marine ecosystems play an important role in well-being through recreation. A 2021/22 report showed people in Wales made approximately 20 million visits to the marine environment, and research shows that most people recognise the positive impact on their mental and physical health. Marine ecosystems also support cultural services including education, research, and spiritual value. Access remains unequal, with inland and lower-income communities facing barriers, though the connection of local communities to their coastal areas remain strong. Wales is the first country in the UK to publish an Ocean Literacy Strategy (published in 2025), with a range of actions proposed to strengthen people’s connections with the marine environment.

Aim 4: Contributing to a Regenerative Economy, Achieving Sustainable Levels of Production and Consumption

The offshore renewables sector in Wales provides an important contribution to the economy; offshore wind investment in Wales reached £103 million in 2023, with future projects expected to create thousands of jobs. Tourism and recreation contribute significantly to the economy, with nearly 20 million marine visits annually. Sustainable tourism could help regenerate ecosystems and communities if managed well. The marine environment also contributes to Wales’ economy through providing a means of global trade, seafood, sand for construction and coastal protection.

Pressures from renewable energy infrastructure, and recreational activities are likely to increase, but evidence, guidance and mapping tools are being developed to support sustainable marine planning. Fisheries management plans and monitoring systems are being implemented to help ensure long-term sustainability. Strategic planning aims to balance development with environmental protection, addressing both the climate and nature emergencies as well as supporting the economy.

Key changes since SoNaRR2020

Since SoNaRR 2020, new evidence has provided more confidence in the assessment of marine habitat condition and a better understanding of the key pressures which include water pollution. The condition of marine intertidal habitats and the extent of subtidal habitats have deteriorated. Seabird populations have suffered sharp declines due to Highly Pathogenic Avian Influenza.

The effects of climate change are becoming more evident and increasing for marine and coastal ecosystems, and new evidence predicts significant effects due to coastal squeeze. The planned expansion of offshore renewable energy has accelerated since the introduction of net zero targets and this presents both opportunities and challenges in responding to the climate and nature emergencies.

The improved evidence base is supporting the development of more targeted actions to enhance the resilience of marine and coastal ecosystems. These restoration and recovery agendas are receiving increased and needed attention, and identifying and developing sustainable funding mechanisms to support delivery is a priority. The publication of an Ocean Literacy Strategy for Wales in 2025 represents an opportunity to increase capacity and engagement, promote behaviour for sustainable use of marine resources and increase access to well-being benefits.

Read the full assessment of the Marine ecosystem in our State of Natural Resources Report 2025.

Underlying evidence

In writing our assessments and to better identify opportunities for action we have gathered evidence that helps us understand these key aspects:

• the drivers of change and pressures on the marine ecosystem in Wales.
• the ecosystem resilience of the marine ecosystem in Wales.
• the benefits, or services, we get from the marine ecosystem and how changes in the state of the marine ecosystem impact on well-being.

Access the detailed evidence through our SoNaRR 2025 Evidence portal.

View full screen version.

Evidence needs

One of our key evidence needs in the marine ecosystem is to have a better understanding of the extent and condition of our habitats and species and the underlying physical conditions and processes that support them. These gaps hinder the ability to evaluate ecosystem condition, biodiversity, and the effectiveness of Marine Protected Areas. Other evidence needs for the marine ecosystem in Wales focus heavily on understanding pressures and impacts from human activities. Key gaps include the extent, distribution, and effects of commercial and also recreational fishing, including bycatch of marine mammals, impacts on fragile habitats, and the sustainability of fisheries. There is also a need to assess the consequences of nutrient inputs and invasive non-native species.

Further evidence is required to understand ecological functions and services, such as carbon sequestration, sediment and other physical processes. Addressing these gaps will support more robust assessments of the state of marine environments and inform sustainable management strategies under SoNaRR.

Key evidence sources

Explore some of the evidence we have used to inform our assessment:

• SoNaRR 2020 Marine assessment
• Condition assessments for Welsh European marine sites
• First Habitats Regulations 9A Report for Wales 2025 [in prep]
• Marine Climate Change Impact Partnership science reviews
• Marine Energy Wales: State of the Sector 2023
• MOAT – Marine Online Assessment Tool
• NRW Marine Evidence Reports
• People and Nature Survey for Wales
• UK Natural Capital Accounts
  
  

Case studies

Project seagrass

Project Seagrass have teamed with several other partners to create the Seagrass Ocean Rescue project. Their current project in North Wales is currently the largest active seagrass restoration project in the UK and is pioneering seagrass restoration methodologies.

SOR North Wales - Project Seagrass

Estimating Carbon Sink Potential

Blue carbon is the carbon stored and sequestered by marine habitats. Estimating the blue carbon potential of Welsh waters allows a greater understanding of how Welsh marine ecosystems contribute to offsetting the release of carbon through human activities. This study has estimated the carbon sink potential of the Welsh marine environment.

Estimating the Carbon Sink Potential of the Welsh Marine Environment PDF

Polders Project, Rumney Great Wharf

This project seeks to restore saltmarsh along the Rumney Great Wharf by reinstating and extending the sedimentation polders. Polders involve the installation of fences in a rectangular pattern, to reduce water movement, which will allow saltmarsh to form over time.

Natural Resources Wales / Restored saltmarsh habitat will help enhance coastal ecosystem and reduce flood risk