Science1 publisher2 min readPublished
Video surveys off Scilly recorded more than 90 seabed species at ten sites outside MPAs
A Plymouth-led team says the sediment mosaics it filmed are not fully described by the EUNIS habitat classes that guide UK marine management, on ground left free of bottom-towed gear for more than ten years.
The Scientist · Science desk
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What happened
- A University of Plymouth-led team, working with local fishers and conservation managers, ran towed and baited video surveys at ten locations outside existing marine protected areas around the Isles of Scilly.
- The surveys turned up a mosaic of sediment habitats that included sandy bedforms as well as boulders and cobbles lying over sand, at depths of up to 90 metres.
- Those habitats supported more than 90 species of seabed animals, including corals, sponges, worms, sharks, rays and starfish.
- Further analysis showed the diversity of sediment habitats is not fully captured by the habitat classifications within the European Nature Information System.
- The team concludes that UK sediment habitat classifications may rest on shifted baselines, describing seabed as it looks after decades of human activity instead of at its best.
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Why it matters
- constraint Sensitivity follows the assigned class, and the animals in frame do not change it, so a class that under-describes a patch of seabed limits the protection a manager can argue for at that spot.
- cost The ecological baselines the authors want come from repeat survey work they themselves call costly and time-consuming, and that spending falls on regulators and monitoring programmes.
- decision Anyone setting condition targets for UK sediment habitats now has a candidate reference point: seabed rested from trawling and dredging for more than ten years. Adopting it raises the bar.
- precedent If the shifted-baseline reading is accepted for Scilly, any UK sediment class described from already-worked ground is open to the same challenge.
UK marine management works in EUNIS classes. A patch of seabed is assigned to one, and the description and sensitivity attached to that class inform decisions about what human activities are permitted there [7]. The Plymouth-led team's finding is that the ground it filmed does not fit cleanly: the mosaic of sandy bedforms and of boulders and cobbles over sand is not fully captured by the marine EUNIS classifications [2][5]. Upright animals such as sponges can shelter other species and increase the sensitivity of a habitat, and the same sediments can act as nursery and feeding areas for species of commercial and conservation importance [4].
Ten locations were surveyed, all outside existing marine protected areas, using towed and baited video at depths reaching 90 metres [1][2]. More than 90 seabed animal species were recorded across those ten sites, which works out to at least nine per site [3][15]. The published account reports a species list, not densities.
The shifted-baselines argument rests on the history of the ground. "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," said Rebecca Turley, a PhD researcher and the paper's first author [12]. Turley also said that "where shifting baselines affect habitat classifications, they will need updating to ensure that marine habitats are appropriately protected in the future" [13].
What that supports is a mismatch between one recovering archipelago and the classes written for UK sediments [5][6]. It does not measure how far off those classes are anywhere else. The comparison here sets recovering ground against a classification scheme, not against trawled ground filmed with the same cameras. Whether the gap holds on seabed still worked by bottom-towed gear is untested.
The team's three recommendations are a review of classifications and sensitivity assessments, with MPA integrity and effectiveness at risk if it is not done [9]; monitoring to determine ecological baselines and recovery [10]; and management of each MPA on the habitats and species found throughout the site instead of on individual habitat features [11]. "The new understanding of sediment habitats confirms that current marine management policies, such as EUNIS classifications, reflect shifted baselines," said Emma Sheehan, professor of marine ecology [14]. The work is published in the Journal of Applied Ecology [8].
What to watch
- Whether UK conservation agencies open a review of the EUNIS sediment classes or of the sensitivity assessments attached to them.
- Whether anyone repeats the towed and baited video protocol on ground still worked by bottom-towed gear. A repeat there would turn the shifted-baseline inference into a measured contrast.
- Whether any of the ten surveyed locations, all currently outside MPA boundaries, are proposed for spatial protection.