Restoring Scilly’s biodiversity
The Scott-Gatty/Bromley conservation research project
Kristian Metcalfe, Richard Sherley and Alice Trevail
On the Isles of Scilly, seabird populations are recovering slowly after decades of decline caused by invasive rats. But their return promises benefits that extend beyond the islands’ cliffs and shores, reaching into the hidden seagrass meadows growing just beneath the waves.
Seabirds are natural ecosystem engineers. They transport marine-derived nutrients, particularly nitrogen, which is often scarce on islands, back to land and coastal zones through their guano, dropped prey, and feathers. These nutrients boost soil fertility and influence biodiversity across terrestrial, intertidal, and subtidal zones, including seagrass meadows, which support marine life and store blue carbon.
“Research like this helps us understand how restoring local ecosystems can have far-reaching benefits for marine environments globally, particularly in the face of climate change and biodiversity loss,” says Professor Kristian Metcalfe.
The challenge has always been proving the connection. While rat-free islands in the archipelago have higher seabird densities, it remains unclear whether those nutrients reach and benefit seagrass beds, and if so, what threshold of seabird recovery is needed.
A research team from the University of Exeter has been working to find out. Professors Kristian Metcalfe and Richard Sherley, together with Dr Alice Trevail and PhD student Sabiya Sheikh, surveyed 22 sites across the Isles of Scilly, including rat-present and rat-free islands. In 2025, thanks to donor funding from Exeter alumni Susan Scott-Gatty, and Kate and Paul Bromley, the team added snorkel-collected seagrass samples from multiple locations.
The result is a growing body of evidence that seabird-derived nitrogen enriches intertidal and terrestrial samples, particularly in limpets and turf algae on rat free islands. Rat free islands also showed greater species richness, including indicator species like keelworm and harpoon weed.
While the trend in seagrass samples suggests nitrogen enrichment linked to the presence of seabirds, the findings need to be validated with greater statistical gathering and analysis. With fieldwork continuing in 2026, the project is building the evidence base needed to support archipelago-wide rat eradication and restore biodiversity and ecosystem resilience.
“Our aim is to understand how seabird recovery can support wider ecosystem health, including seagrass,” the team notes. “This will help us evaluate the full benefits of rat eradication across the archipelago,” says Dr Alice Trevail, Ecology and Conservation Research Fellow.
The work of the team on the Scilly Isles would not have been possible without the generosity of Susan, Kate and Paul.