Subtidal sandbanks are slightly covered by sea water at all times to depths of up to 20 metres below low water mark. They include muddy sands, clean sands and maerl beds (carpets of small, unattached, calcareous seaweed).

Unlike mud and sandflats, subtidal sandbanks are not exposed to drying out. However, as with many coastal features they are affected to varying degrees by wave action. For example, the subtidal sandbanks in the Solway Firth are heavily influenced by strong tidal streams, which can move the sandbanks some distance over the period of one tidal cycle.

Wave action, particularly during storms, may affect sandbanks up to a depth of 50m. This disturbance is likely to be more observable in shallow water areas and may result in a great deal of sediment transport. Often this movement of sediment in shallow or constricted areas can cause the water above the banks to become very turbid.

Subtidal sandbanks also support benthic or burrowing communities and, as with intertidal mud and sandflats, the nature and location of these communities is largely determined by the nature of the sediment which forms the sandbank.

There are a number of human activities and provisions that can have a long term effect on the stability of subtidal sandbanks. These include:

• dredging and aggregate extraction
• provision of recreational facilities (jetties and harbours etc.)
• pollution

As subtidal sandbanks are, by their nature, the result of relatively high energy conditions, they are likely to be flexible to changes caused by storms or human activities. For example, Poiner and Kennedy (1984) note an initial increase in species richness following dredging.

The tables below summarise the potential threats to subtidal sandbanks from land and waterborne processes.

Water based Processes

Land based processes

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