Australia's coastline supports extensive blue carbon ecosystems, including mangroves, saltmarshes, tidal wetlands and seagrass meadows. These habitats contribute to climate regulation, biodiversity conservation and coastal resilience.

Blue carbon refers to atmospheric carbon dioxide (CO₂) absorbed and stored in the vegetation and sediments of coastal ecosystems. These habitats cover a relatively small area globally – about 5% of the sea floor by area – yet they account for a disproportionately large share (about half) of carbon burial capacity due to their deep, waterlogged soils, which slow decomposition and lock away carbon over long periods (centuries to millennia).

Australia has lost substantial areas of coastal habitat since European settlement. Estimates of historical losses vary by ecosystem and location, highlighting the importance of protecting remaining habitats as well as restoring degraded areas.

The benefits of restoration vary between ecosystems and sites. Restoration should therefore begin with clear objectives and an understanding of the ecological processes that sustain the habitat.

Protecting intact ecosystems is particularly important because restoration can be expensive, take many years and may not fully recover the functions of a mature habitat. Restoration complements, rather than replaces, the protection of existing blue carbon ecosystems.

When blue carbon coastal ecosystems are drained or disturbed – such as for building development or agriculture – they can lose ecological function and release plumes of carbon dioxide back into the atmosphere, contributing to climate change. The amount released depends on the ecosystem, the type and extent of disturbance, and site conditions.

Restoring degraded habitats can help recover carbon-storage capacity while also improving biodiversity and other ecosystem services. In some circumstances, carbon-credit revenue can help meet restoration and management costs.

However, not every restoration project is eligible for carbon credits, and not every eligible project is financially viable. Project developers need to consider:

• the eligibility requirements of the applicable carbon-credit method
• the likely quantity and timing of credits
• feasibility studies, restoration and monitoring costs
• land tenure, legal rights and governance arrangements
• reporting, permanence and other ongoing obligations
• carbon-credit prices and access to buyers
• other funding sources and the project's wider environmental and cultural objectives.

Carbon finance should be considered alongside grants, government programmes, philanthropic funding, partnerships and other mechanisms that can support coastal restoration.

Habitat restoration has a nationally significant carbon sequestration potential. Australia has pioneered implementing blue-carbon-based strategies to help meet its carbon commitments under the 2016 Paris Agreement.

Australia's Australian Carbon Credit Unit (ACCU) Scheme provides a framework through which eligible projects can earn credits for emissions reductions or carbon sequestration.

The tidal restoration of blue carbon ecosystems method enables eligible projects to generate ACCUs by restoring tidal inundation to certain previously drained coastal wetlands. This may involve removing or modifying structures such as sea walls, levees or bunds to allow tidal water to return.

The method uses the Blue Carbon Accounting Model (BlueCAM) to estimate abatement in accordance with the method's requirements. Project proponents must meet applicable eligibility, monitoring, reporting and other requirements.

Credits may provide revenue to support project implementation and ongoing management, but the financial return depends on the amount of eligible abatement, project costs, crediting arrangements and market conditions.

Other approaches to blue carbon restoration and accounting are also being investigated. These include activities that protect or restore vegetation and reduce damage to coastal habitats. Such activities should not be assumed to generate ACCUs unless they meet the requirements of an applicable, current method.

Additional methods are being explored to expand the scope of blue carbon accounting through vegetation protection, grazing exclusion, and broader habitat restoration.

For example, research is collecting baseline data for a blue carbon method based on restoring wetland habitat by fencing the area to exclude damage-causing farmed and feral non-native ungulates such as cattle and pigs.

Traditional Owners have enduring relationships with coastal Country and hold knowledge that can contribute to the protection, restoration and management of blue carbon ecosystems.

Blue carbon projects can create opportunities for employment, skills development, cultural knowledge transmission, ecological monitoring and long-term stewardship. They may also provide opportunities to participate in carbon markets and shape decisions about the future management of Country.

Indigenous leadership should be considered part of project governance, rather than an additional benefit to be pursued after the project has been designed. Effective projects recognise Traditional Owner rights, priorities and governance arrangements from the earliest planning stage.

Australian states and territories have different coastal environments, restoration priorities and policy settings. Local case studies can help practitioners understand how projects are developed, funded and implemented in different contexts.

Research has identified several factors that improve coastal habitat restoration efforts. In tidal wetland regeneration, for example, these factors include the following.

• Select the right site, which includes avoiding sites with excess erosion or sediment deposition
• Select the right plant species for the region, and minimising stress on plants such as poor soil nutrients or the impact of herbivores.
• Use strategies such as planting in high density clumps, with high species diversity, and fertilising the soil.
• Consider projected climate change – note the poleward shift of ecosystems due to rising temperatures – to future-proof restoration efforts at certain points along the coast.

Long-term monitoring and adaptive management are also important because restoration outcomes can vary considerably among sites and over time.

Coastal land tenure can complicate restoration, particularly where habitats extend across public and private land or where coastal boundaries shift over time. Questions about ownership, access, decision-making authority and the right to undertake restoration may affect both project implementation and carbon-credit eligibility.

In most Australian states and territories, the ‘mean high water mark’ defines the legal boundary between private property and public land along the coast. This ambiguous and dynamic boundary can result in a lack of clarity as to whether mangrove and tidal wetland habitats are located on public or private land, or straddle both.

Early engagement with tenure – boundary ambiguity and legal rights, including rights of Traditional Owners – clarified through contractual agreements at the start of any blue carbon habitat restoration project.

This step adds time and expense; researchers have called for policy and law reform to reduce this barrier to blue carbon ecosystem restoration.

Coastal development and infrastructure can prevent mangroves, saltmarshes and other coastal habitats from moving inland as sea levels rise. This process, known as coastal squeeze, can reduce habitat extent and undermine restoration outcomes.

Project planning should consider future habitat distributions, opportunities to protect migration corridors and the implications of nearby infrastructure and land-use decisions. Restoration should be integrated with broader coastal planning wherever possible.

This should be considered during project planning and site selection.

Restoration outcomes can vary depending on site conditions, ecological responses, and climate impacts. In addition, future risks such as sea-level rise, marine heatwaves, cyclones and changing sediment regimes may affect long-term ecosystem condition and carbon storage.

This uncertainty can present challenges for investors and project developers, reinforcing the need for adaptive management, robust monitoring and realistic expectations about project performance over time.

Blue carbon restoration presents a significant opportunity to deliver climate, biodiversity and cultural benefits simultaneously. However, achieving these outcomes requires more than efforts in ecological restoration alone.

Success depends on integrated approaches that combine robust scientific knowledge, supportive policy and carbon-market frameworks, clear governance and tenure arrangements, and meaningful, long-term partnerships with Indigenous communities.

Carbon projects also face financial and regulatory uncertainty. Revenue depends on eligible abatement, project costs, market conditions and compliance with the applicable method. Carbon-credit income should not be assumed to cover all restoration and management costs.