Seabed surveys around the Isles of Scilly find more than 90 species across habitats poorly captured by classifications

Scientists have conducted an unprecedented assessment of the seabed around the Isles of Scilly, revealing complex mosaics of sediment that support a wide range of habitat-building species. The research, led by the University of Plymouth, used a range of techniques to monitor sediments around the archipelago and explore the diversity of species living within them.

Working with local fishers and conservation managers, the study team carried out towed and baited video surveys at 10 locations outside existing marine protected areas (MPAs). The surveys uncovered an array of sediment habitats—from sandy bedforms to boulders and cobbles over sand—at depths of up to 90 meters (295 feet) below the ocean surface.

The habitats were found to support more than 90 species of seabed animals, ranging from corals and sponges to worms, sharks, rays and starfish. Many upright species on the seabed, such as sponges, could provide refuge for other species and increase habitat sensitivity. These habitats can also create nursery and feeding areas for species of commercial and conservation importance.

However, further analysis showed that this diversity of sediment habitats is not fully captured by habitat classifications within the European Nature Information System (EUNIS). Marine EUNIS classifications are designed to describe habitats and the species living in particular parts of the ocean. They can inform conservation management decisions and policies on human activities.

The findings, published in the Journal of Applied Ecology, have led the study team to suggest that classifications for sediment habitats around the U.K. may be based on shifted baselines—information reflecting how a habitat appears after decades of human activity, rather than what it could look like in the best-case scenario for its composition and health.

“Many of the sediment habitats around the Isles of Scilly have not been trawled or dredged for over a decade. So, it provides a really good example of what a recovering seabed can look like. Our study has filled significant gaps in knowledge about the diverse species that can thrive in sediment habitats unimpacted by bottom-towed fishing gear for more than 10 years. However, where shifting baselines affect habitat classifications, they will need updating to ensure that marine habitats are appropriately protected in the future,” said Rebecca Turley, a Ph.D. researcher.

Based on their findings, the researchers made three recommendations they believe could improve future decisions concerning the Isles of Scilly and other U.K. locations. They are:

• Marine management should shift away from reliance on rigid EUNIS classification frameworks, and that classifications and sensitivity assessments be reviewed to capture new evidence, or MPA integrity and effectiveness could be at risk
• Robust monitoring—despite the fact that it can be costly and time-consuming—should be put in place to determine ecological baselines and recovery
• MPAs must be managed based on the habitats and species found throughout each site, rather than focusing on individual habitat features, to better protect marine ecosystems.

“The new understanding of sediment habitats confirms that current marine management policies, such as EUNIS classifications, reflect shifted baselines. For MPAs to be effective tools for marine conservation, we need to address any uncertainties in existing habitat classifications and sensitivity assessments, amend marine habitat condition targets and update spatial measures in conservation planning. Through our recommendations, we could move closer to an ecosystem approach that properly enhances the recovery and conservation of both habitats and species,” said Emma Sheehan, professor of marine ecology.

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Lisa Lock

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Andrew Zinin

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