Natural marine habitats like kelp forests and seagrass beds could play a vital role in protecting Scotland’s coastline from flooding and erosion by mitigating the impact of waves hitting its shorelines by as much as 70%, researchers suggest.

According to new modelling evidence produced by scientists from Heriot-Watt University, kelp forests, seagrass beds, and even oyster reefs could help protect coastlines from Uist to Orkney by dampening wave energy and reducing the risks of flooding.

The study, commissioned by the Centre of Expertise for Waters, used advanced computer modelling to stimulate how these habitats absorb wave energy, finding kelp beds to be especially effective by potentially cutting wave height by as much as 70% in some areas.

The researchers focused their attention on two study locations that are currently highly exposed to storms and rising sea levels: Sanday in Orkney and Uist in the Outer Hebrides. To assess the wave-dampening effect of different marine habitats, they used extreme offshore wave conditions – those expected once every 100 years – detailed seabed maps, and habitat properties to drive a nearshore wave model.

This allowed them to test how factors like wave exposure, water depths, and the physical characteristics of habitats – such as the density, height, and shape of seaweed or seagrasses – and the extent of those habitats influence how much wave energy is reduced before reaching the shore. 

They predict that for somewhere like Sanday in Orkney, the presence of kelp could reduce wave heights by up to 25% during severe conditions. In Uist, potential reductions reached up to 70%.

The other habitats studied absorb less wave energy because they are not typically found in highly wave-exposed areas. While these other habitats do help reduce wave energy to some extent, they are themselves more vulnerable to damage during extreme events since they need more time to recover and restore to remain effective over time.

According to Professor Qingping Zou, professor of coastal dynamics at Heriot-Watt’s Lyell Centre, coastal flooding and erosion are becoming increasing concerns across Scotland where winter storms are intensifying.

“While hard infrastructure like sea walls is one option to help protect coastal communities and assets, this study shows the potential of nature-based solutions for flood risk management,” said Zou. “Our model shows that established kelp and seagrass beds could act like underwater forests. They could reduce the power of waves and help stabilise the sea floor.

“With the right protection and investment, these habitats could form a key part of Scotland’s climate resilience strategy.”

Professor Joanne Porter is based at Heriot-Watt’s Orkney campus and is a co-author of the report. She concludes that habitats like kelp and even blue mussel beds act as powerful buffers against storms, but that these ecosystems are also fragile. They will therefore require careful management and protection to be incorporated effectively into local flood defences.

“The lower lying islands of Orkney, like Sanday, have large areas of kelp forest fringing, particularly on the east side,” she said. “If it were to be damaged, valuable coastal protection for village communities would be lost, along with other benefits it brings, such as carbon storage and habitat for species of commercial fisheries value.

“These ecosystems are also concentrated along Scotland’s west coast and islands, in contrast with the east coast, which has fewer due to exposed conditions and the impact of historical overharvesting.”

The team says that these findings highlight the need of policymakers to better integrate marine habitat protection into flood defence strategies.

Professor Qingping Zou, added: “Ideally, we would prioritise habitat protection and restoration in the most vulnerable coastal areas and make long-term commitments to projects and boost these underwater forests and beds.”

This report has been published on the Centre of Expertise for Waters website. The Centre aims to deliver research needed to help protect and improve the water environment and engage with stakeholders and communities to maximise the impact of this research. 

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