Ocean sediments and shifting baselines—A call to revise European habitat classifications

Many ocean sediment habitats on the continental shelf have been extensively trawled and dredged with bottom‐towed fishing gear before scientific baselines of the seabed could be recorded. Observations of ocean sediments may reflect shifted baselines towards more mobile and homogenous environments, dominated by disturbance‐tolerant, short‐lived species. This will have implications for the appropriateness of existing Marine Protected Area (MPA) management.

Low levels of trawling and dredging in the Isles of Scilly provide an opportunity to study a UK example of minimally impacted sediment habitats, where absence of bottom‐towed fishing since 2013 has provided the chance for 10 years of ecological recovery. Here, we present data from towed and baited remote underwater video surveys between 2023 and 2025, to examine habitat composition, and epifaunal and demersal species assemblages in the study area.

Results revealed heterogeneous sediment habitats colonised by juvenile elasmobranchs and distinct epifaunal assemblages. This included upright fragile, structure‐building species, such as sponges and corals.

The presence of these species in sediment habitats increases ecological vulnerability to disturbance by bottom‐towed fishing gear.

The European standard framework for classifying ocean sediments, ‘EUNIS’, does not include representative categories for the species assemblages observed and predefined habitat classifications do not explicitly capture the spatial variation observed in sediment substrata. This will have potential implications for associated sensitivity assessments (‘MarESA’) often used in MPA management.

Synthesis and applications . Shifting baselines affect the appropriateness of existing habitat classification frameworks, potentially reducing MPA integrity and efficacy. To enable representative mapping, accurate sensitivity assessments and appropriate management of marine habitats, EUNIS classifications require more flexibility. We highlight evidence gaps and solutions to improve habitat classifications, discuss a limitation of feature‐based MPAs and advocate for robust monitoring to capture spatial variation in sediment habitats. Maintaining whole‐site integrity in MPA management would enhance spatial connectivity of heterogeneous habitats, furthering targets for marine recovery and conservation.