Intertidal and continental shelf
Scotland has an extensive and varied coastline comprising approximately 50% rocky and 50% sedimentary intertidal habitat. Large stretches of the Mainland west coast and Northern Isles are predominantly rocky whereas on the west coast of the Outer Hebrides and the Mainland east coast it is much more patchy with rocky shores and cliffs interspersed by large stretches of sandy and muddy coastline. Intertidal habitats are affected by numerous physical variables including wave exposure, salinity, temperature and tides which dictate what animals and plants are found on specific shores. The subtidal communities are strongly affected by factors such as the availability of light, wave action, tidal stream strength and salinity. Rocky shallow continental shelf habitats are typically dominated by seaweeds and in deeper areas below the photic zone (about 50 m) communities comprise exclusively animals. Shallow subtidal sediments in places support habitats such as seagrass beds and maerl, a red seaweed with a hard chalky skeleton that forms small twig-like nodules which accumulate to form loosely interlocking beds, creating the ideal habitat for a diverse community of organisms. Typically sedimentary habitats are dominated by a range of burrowing animal species.
The Biogenic habitats assessment catalogues the loss in extent of six biogenic habitats (all Priority Marine Features): blue mussel, horse mussel, flame shell, maerl, seagrass beds, and serpulid aggregations. The Predicted extent of physical disturbance to seafloor assessment uses the degree of exposure to demersal fishing activity as a proxy for habitat condition. The Intertidal seagrass assessment is a first attempt to understand the ecological health of Scottish intertidal seagrass and is restricted to six sites.
The Case study: Biogenic habitat enhancement highlights the efforts now being made to enhance the status of some biogenic habitats through activities aimed at aiding their recovery and restoration. In other cases, where damage to Priority Marine Features has occurred, positive action is taken as demonstrated in the Case study: Protecting the Loch Carron flame shell beds where emergency measures were put in place to prevent further damage and subsequently a Marine protected Area was designated. The fact the prevention is better than cure is illustrated by the Case study: Persistent damage to the Loch Creran serpulid reefs where damage that was first observed in 1998 still shows little evidence of recovery. The value of long-term monitoring of specific sites is illustrated by the Case study: Intertidal rock which highlights how looking at changes at a community scale helps separate natural variations on species abundances from longer term community trends. The growing awareness of natural capital and ecosystem services provided by the marine environment is illustrated by the three case studies Case study: Blue carbon in Scottish maerl beds; Case study: Blue carbon in Scottish marine sedimentary environments; Case study: Blue carbon: the contribution from seaweed detritus which highlight the importance of marine habitats in climate change mitigation through the capture and storage of blue carbon, and the need for the protection of such habitats from various anthropogenic activities. Despite a long history of intertidal and subtidal survey work there remains significant gaps in knowledge. The Case study: Seabed habitats in territorial waters - the evolving knowledge-base charts the ongoing surveys that have been undertaken by government agencies and citizen science initiatives to further expand and improve the knowledge base.