Building a healthier future for marine ecosystems with Marine Net Gain

Angie de Burgh, Associate Director at GoBe Consultants, part of APEM Group, discusses how MNG will help improve the environment in our oceans and seas. Angie also explores some of the challenges of delivering a pragmatic MNG framework that can deliver measurable benefits.

Q. Angie, can you explain the concept of Marine Net Gain (MNG) and why it’s an important development?

Globally, marine wildlife and the ecosystems that support them are experiencing significant damage and a rapid decline. Human activities such as industrial fishing, coastal development, pollution, climate change, and the spread of invasive species have placed immense pressure on these fragile environments. Immediate action is needed to address these challenges, making initiatives like MNG especially important.

The offshore wind industry is growing quickly, in the UK, Europe and worldwide. This has increased interest in getting good ecological results from these renewable projects. As offshore wind expands, there is increasing interest in ensuring these projects deliver positive ecological outcomes. Meeting clean energy targets requires extensive development, but sustainability is key.

Simply put, MNG requires developers of major marine infrastructure to leave marine environments in a measurably better state than before development. This is an exciting concept and goes well beyond basic mitigation. By integrating biodiversity gains into offshore developments, we have the potential to foster long-term restoration and recovery of our seas and marine wildlife if these efforts are carried out effectively.

While MNG is not yet enshrined in legislation, there is a growing expectation from regulators and nature conservation bodies that developers will voluntarily incorporate MNG initiatives into their projects. This proactive approach is particularly pertinent as the offshore wind and other marine industries continue to expand, emphasising the need for sustainable development practices that contribute positively to marine biodiversity.

Q. Can you give an example of a marine habitat we’ve lost?

Seagrass meadows are crucial for marine biodiversity and coastal protection, yet the UK has lost around 92% since the 1930s due to development, pollution, and disease. These habitats stabilise sediment, maintain water quality, and can absorb carbon, helping reduce greenhouse gases.

Other vital ecosystems, such as kelp forests and salt marshes, are also facing significant decline. Native oyster reefs, which were once abundant, have been reduced by more than 95% since the 19th century. These reefs are vital for water filtration and play an important role in controlling coastal erosion.

With such severe habitat loss, urgent action is needed to restore these essential marine ecosystems.

Q. Why is implementing Biodiversity Net Gain (BNG) in marine environments more challenging than on land?

It is worth saying that BNG does cover the intertidal zone, down to the Mean Low Water mark. This captures the vital interface between land and sea, including areas that are covered and exposed by water during different tide states. However, BNG does not extend to the marine environment beyond this zone.

Marine ecosystems present unique challenges for BNG due to their vast, fluid nature and are largely unseen. Generally speaking, land habitats are familiar, have clear boundaries and are comparatively easier to monitor. Marine environments are largely hidden beneath the surface, making baseline data collection and long-term tracking more difficult and much more expensive. Additionally, the interconnected nature of marine ecosystems adds complexity. A major concern is whether marine biodiversity loss and gain can be measured accurately enough for regulation. The dynamic nature of marine ecosystems, shaped by such factors as seasonal changes and species migrations, can add additional challenges to establishing a reliable baseline.

A Blue Shark is highly migratory, travelling vast distances in search of food. It is often seen off the coasts of SW England, Wales, and Scotland, especially in summer months.

Q. Are there any equivalent measures being used internationally?

Globally, there are similar concepts to Marine Net Gain (MNG) already in place. However, they mainly focus on offsetting impacts instead of creating net gain.

Australia uses environmental offsets for sensitive habitats like the Great Barrier Reef.

The U.S. enforces a “no net loss” policy as part of the Clean Water Act, for wetlands and intertidal zones, supported by mitigation banks – i.e. privately managed lands, restored to compensate for habitat loss. Developers can offset their impacts by purchasing credits from these banks.

Canada’s Fisheries Act mandates habitat compensation for impacts on fish and intertidal zones.

New Zealand applies biodiversity offsets for marine developments under its Resource Management Act.

The EU integrates restoration and compensation into marine spatial planning through frameworks like the Nature Restoration Law.

Notably, the Netherlands marine biodiversity enhancement measures are a key factor in Offshore Wind auctions.

In the UK, Marine Net Gain will do more than just offsetting – it will be a legal requirement to improve the marine environment post-construction. Leasing Round 5 in the Celtic Sea features a comparable initiative.

The Crown Estate states, “Our goal is to drive progress towards a net positive outcome for biodiversity and strengthen the resilience of marine ecosystems through Round 5.”

Q. So, when can we expect to see MNG become legislation, and what do you think it will look like?

The introduction of Marine Net Gain in England is being progressed through the UK Government’s legislative programme, with enabling powers set out under the Environment Act 2021. Secondary legislation is expected to be brought forward via statutory instruments in Parliament, following public consultations and the development of detailed policy and guidance. The Department for Environment, Food and Rural Affairs (Defra) is leading on policy development, with MNG anticipated to be implemented in the mid-2020s, aligning with broader marine planning and licensing reforms.

In terms of delivery, the Marine Management Organisation (MMO) will play a central role in administering and enforcing MNG within the marine licensing process, while Natural England (NE) will support ecological assessment and advice, and The Crown Estate (TCE) will influence implementation through its role in seabed leasing and long-term stewardship. It is important to note that MNG applies to English waters only; the devolved administrations of Scotland, Wales, and Northern Ireland are developing their own approaches to marine biodiversity enhancement, and close coordination will be essential to ensure consistency and alignment across UK waters.

Northern Gannet flying over marine waters — a key seabird species highlighting the importance of marine biodiversity and habitat restoration

The short-term approach to developing a framework for MNG involves making decisions within the consenting process that focus on ecological targets. This requires consistent, proportionate assessments of how a project’s impact relates to these targets, using available techniques and evidence. While the natural capital evidence base is not yet robust enough to quantitatively measure ecological change for regulatory purposes, it remains valuable for understanding the ecological, social, and economic value of different gain measures. It can also guide decisions on how to best achieve strategic environmental goals and should be further developed in this context. Regarding how it may look, an effective framework must balance ecological ambition with feasibility, ensuring meaningful outcomes without excessive bureaucracy

It is likely that MNG will mirror BNG, potentially requiring marine developers to leave the environment in a better state than before by, for example, a 10% net gain. This process would require a collaborative, multi-stakeholder approach involving industry, conservation organisations, and local communities.

A key unknown at this time is how success would be measured. However, emerging thinking points to measuring improvements in marine biodiversity, including the extent, condition, and function of habitats and species compared to a defined baseline. This would involve demonstrating clear ecological gains, supported by robust, quantifiable metrics and monitoring tools. Success also depends on the meaningful involvement of stakeholders, such as local communities and industries, alongside clear governance frameworks and effective implementation. Long-term resilience, including the permanence of ecological gains and their adaptability to climate change, is essential to ensure that net gain outcomes are sustained well into the future.

Q. So we’re not sure what the legislation will look like yet, but what could marine habitat restoration look like in practice?

Even without formal legislation, many developers are actively pursuing initiatives to achieve positive ecological outcomes, often driven by their own sustainability targets and intuition on nature-inclusive design.

For example, offshore wind farms are using reef cubes and graded granite and rock material around turbines and cables to mimic natural habitats, creating refuges and breeding grounds for marine species. These ‘nature-inclusive’ designs help enhance local biodiversity and support commercially important species such as lobsters and crabs by forming artificial reefs.

The Ørsted Humber Biodiversity Restoration Project, launched in August 2022, is a key example of a restoration initiative in partnership with the Lincolnshire and Yorkshire Wildlife Trusts aimed at restoring biodiversity and enhancing climate resilience around the Humber Estuary. The project involves planting 3 hectares of saltmarsh, restoring 4 hectares of seagrass, and creating a native oyster reef, building on Ørsted’s ongoing seagrass restoration efforts linked to the Hornsea Project Four Offshore Wind Farm. These habitat restoration efforts are part of Ørsted’s broader commitment to combating climate change and supporting nature, helping to safeguard vital coastal ecosystems while contributing to global sustainability goals.

Seagrass meadows are crucial marine habitats that stabilise coastlines, support marine biodiversity, and play a key role in carbon sequestration.

Q: How can APEM Group help developers to navigate MNG?

We’ve been advising developers for nearly four years on how to integrate MNG principles into their projects. Our approach is grounded in the mitigation hierarchy, with an emphasis on avoiding irreplaceable habitats, and we’ve utilised innovative solutions like reef cubes and graded granite to provide habitats that support marine biodiversity, including working with partners to tailor solutions to specific species.

APEM has the UK’s largest team of marine ecology consultants, home to 280 practitioners in total. We are passionate about the conservation and enhancement of marine ecology and the wise use of our marine environment. Our work is backed by strong academic partnerships and hands-on experience in marine habitat restoration. From oyster and seagrass surveys to tailored restoration strategies, we blend cutting-edge research with practical expertise to develop science-led solutions. We have also collaborated with companies pioneering ecological engineering solutions and notably served as the lead authors for NatureScot’s “Marine and Coastal Enhancement Projects within Scottish Inshore Waters: Guidance on Scoping a Proposal”¹.

Shaping the future of MNG is also a key focus, with our teams in APEM Group actively participating in working groups and consultations. By staying ahead of emerging policies, we ensure our advice remains scientifically robust and aligned with future regulations.

Marine Net Gain is coming, and no doubt there will be complexities to navigate – but as the framework takes shape, we’re in a great position to help developers meet their commercial objectives whilst achieving meaningful ecological outcomes.

References:

1 NatureScot – Marine and coastal enhancement projects within Scottish inshore waters guidance scoping proposal