Designing coastal infrastructure that works with nature

Rising sea levels, intensifying storms and accelerating coastal development are placing unprecedented pressure on already modified shorelines. Engineered structures such as seawalls and breakwaters now dominate many urban waterfronts and roughly one-third of the world’s sandy coastline has been hardened. In many cities, hard infrastructure has become the default response to coastal risk.

This reliance on hard infrastructure provides essential protection for coastal communities and assets. Conventional armouring reduces erosion, buffers storm surge and stabilises valuable land. However, this protection comes at an ecological cost.

Evidence from seawalls, one of the most common forms of coastal defence, illustrates the impact. Compared with natural shorelines, they support 23 percent lower biodiversity and 45 percent fewer organisms. Over time, hardened coastal infrastructure reshapes ecosystems, simplifying environments that were once structurally complex and biologically rich.

Coastal protection and ecological outcomes are often treated as competing objectives, with safety prioritised over nature. However, this tension is not inherent to coastal defence. In many cases, it reflects how shoreline protection has traditionally been designed.

Research increasingly suggests that this trade-off is not inevitable. Eco-engineering introduces modest design enhancements that retain protective function while restoring ecological complexity.

A global review of 160 marine eco-engineering interventions found strong and increasing evidence of impact, with nearly 90 percent reporting positive ecological outcomes, including greater species abundance and richness. In urbanised marine environments, eco-engineering is emerging as a practical, design-led way to deliver both coastal resilience and biodiversity outcomes.

As climate risk accelerates and shorelines continue to urbanise, these findings have important implications for coastal infrastructure design. The challenge now is to move beyond conventional armouring and design coastal infrastructure that supports both protective and ecological functions.

Coastal infrastructure has traditionally been designed to prioritise stability and durability. As a result, many seawalls, revetments and breakwaters are smooth, vertical and structurally simplified, unlike the irregular surfaces and crevices of natural rocky shorelines. Research shows that seawalls are typically 20 to 40 percent less structurally complex than nearby natural rocky shorelines at scales relevant to marine organisms.

The lower structural complexity of many artificial coastal structures limits the microhabitats available to various species. With fewer refuges from predators, tidal exposure and wave energy, these surfaces tend to host less diverse communities than natural rocky habitats. Coastal infrastructure can also fragment habitats and disrupt ecological connectivity, while new surfaces created by artificial structures may facilitate the spread of non-indigenous species.

At the same time, the scale of existing coastal armouring means that large-scale removal or replacement is rarely feasible. Many cities depend on these structures for flood protection and shoreline stability, and rebuilding entire coastal defence systems would be both costly and disruptive. The more realistic path forward is to enhance the ecological performance of infrastructure that is already in place.

Improving the ecological performance of coastal infrastructure does not require large-scale reconstruction. In many cases, modest design interventions can be integrated into existing structures while maintaining their protective function.

Retrofitted enhancements. Many widely tested eco-engineering interventions focus on increasing the structural complexity of coastal infrastructure. By introducing features such as ridges, crevices and water-retaining pools, these enhancements create habitat conditions that more closely resemble natural rocky environments.

In Sydney Harbour, Living Seawall panels installed on existing seawalls supported at least 36 percent more species than unmodified structures. Artificial rockpools have produced similar results. In the United Kingdom, rockpools installed on vertical concrete seawalls increased species richness by creating water-retaining refuges for marine organisms. Other design modifications, including pits and grooves, can also introduce microhabitats on otherwise smooth surfaces.

Additionally, targeted transplants such as oysters or seaweeds can help establish habitat on enhanced structures. In Staten Island, New York, the Living Breakwaters coastal resilience project is installing live oysters on enhanced breakwaters to rebuild reef habitat, increase biodiversity and strengthen shoreline protection.

Integrated or hybrid solutions. When new coastal infrastructure is built or major upgrades occur, ecological features can be incorporated directly into the design. These approaches combine conventional engineering with ecological enhancements from the outset.

Seattle’s redesigned seawall incorporates textured surfaces, underwater rock beds and light-permeable sidewalks that allow sunlight to reach the water below, improving conditions for migrating juvenile salmon in Elliott Bay. Other hybrid approaches include living shorelines and oyster reefs in low-energy environments, as well as modular habitat units and artificial reefs in urban marinas. In one study, artificial fish nurseries installed in ports hosted more than twice as many fish as bare docks while supporting greater species diversity.

These examples demonstrate the growing potential of eco-engineering approaches in coastal infrastructure.

Despite promising results, several evidence gaps continue to limit the wider adoption of eco-engineering in coastal infrastructure, and addressing these gaps will be essential to strengthen design guidance and scale these approaches across different coastal contexts.

• Many projects lack baseline ecological data, making it difficult to assess how communities change over time or design interventions suited to local conditions.
• Monitoring periods are often short, frequently less than a year, limiting understanding of how ecological communities develop over longer timeframes.
• Most studies focus primarily on ecological outcomes, with far fewer evaluating how eco-engineering features influence hydraulic behaviour, structural durability or maintenance requirements.
• The evidence base is geographically uneven, with most projects concentrated in temperate regions and relatively few applications in tropical or other under-represented coastal environments.
• Artificial coastal structures can facilitate the spread of non-indigenous species in ports and marinas, yet relatively few eco-engineering studies explicitly assess these risks.

Scaling eco-engineering from isolated pilots to mainstream coastal practice will require closer integration between ecological science, engineering design and infrastructure management. The most immediate opportunities lie in retrofitting existing seawalls and breakwaters, where habitat features can be incorporated into maintenance cycles or upgrades without major reconstruction. Designs should also be tailored to local conditions such as tidal regimes, climate and species pools, rather than relying on one-size-fits-all solutions.

Ecological enhancements must be treated as engineered elements within coastal infrastructure projects, with appropriate structural checks and simple observations of hydraulic performance and maintenance requirements. Strengthening ecological baselines, extending monitoring periods and expanding applications in tropical and other under-studied regions will be critical for improving the global applicability of eco-engineering approaches.

Over the coming decade, I expect eco-engineering to shift from being retrofitted onto coastal infrastructure to being embedded in the earliest stages of planning and design. As evidence continues to grow, I anticipate these interventions will be increasingly quantified, demonstrating real biodiversity gains and enabling measurable biodiversity credit outcomes.

Eco-engineering demonstrates that protecting coastlines and restoring biodiversity are not inherently competing objectives. With thoughtful, often modest design choices, existing infrastructure can evolve into nature-positive coastal systems that support both resilience and ecological function. The opportunity now is to move beyond pilots and integrate eco-engineering into mainstream coastal infrastructure planning and design.