Drawing lines at the sand: Evidence for functional vs. visual reef boundaries in temperate Marine Protected Areas

•MPAs can either protect all seabed habitats within them or discreet features.•If discreet features are protected humans have to know where the boundaries are.•Following 3 years protection, reef fauna indicated expansion of the reef feature.•MPA management should therefore be site based to allow for shifting baselines.•Site based MPAs will be more effective at delivering ecosystem goods and services.

Marine Protected Areas (MPAs) can either protect all seabed habitats within them or discrete features. If discrete features within the MPA are to be protected humans have to know where the boundaries are. In Lyme Bay, SW England a MPA excluded towed demersal fishing gear from 206 km2 to protect rocky reef habitats and the associated species. The site comprised a mosaic of sedimentary and reef habitats and so 'non reef' habitat also benefited from the MPA. Following 3 years protection, video data showed that sessile Reef Associated Species (RAS) had colonised sedimentary habitat indicating that 'reef' was present. This suggested that the functional extent of the reef was potentially greater than its visual boundary. Feature based MPA management may not adequately protect targeted features, whereas site based management allows for shifting baselines and will be more effective at delivering ecosystem goods and services.