Sand and Gravel

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  1. Habitats explorer
  2. Marine
  3. Sand and Gravel

Sand and Gravel - Credit Jolyon ChesworthSand and Gravel - Credit Jolyon Chesworth

Sand and gravel are formed as a result of weathering and erosion of larger rocks. Due to their size they are easily dispersed and can occur in a great variety of environmental conditions ranging from deep sea, wave-sheltered and exposed coasts, bays and estuaries. The combination will rarely be just gravel or sand but is often a varying combination of the two.

What is it?

Sand and gravel is classified as the seabed and shore that consists of sediments ranging in size from ≥0.0625mm to 2mm for sand and 2mm to 64mm for gravel.

Where is it found?

Sand and gravel can be found covering the seabed from the deep of the ocean to the top of shore. They tend to be less dominant in exposed areas as the strong currents will often carry the sediments away. Sand and gravel cover up to 90% of our seabeds.

This type of seabed can be found off the coast throughout the UK. On the west coast, in the English Channel and Irish Sea, the sand and gravel is mostly shell derived, while those connected to the North Sea have a higher composition of hard rocks.

Why is it important?

There are a whole range of species that live in these areas, a greater number of species is often found in more sheltered areas compared to wave and wind exposed areas.

Sand eels will live in these areas, sometimes in shoals of thousands, they live in these habitats so they can bury into the seabed for protection, they tend to bury over night and also during most of the winter months. They are hugely important in the marine food chain as they are fed on by a whole range of species including commercially important fish such as cod, haddock, bass and rays, which in turn attract other predators such as sharks.

Sand and gravel areas also attract lots of crustaceans, like shrimps prawns and crabs, many of which also burrow in to the sediment.

Cuttlefish are also often found in these areas, these incredible creatures are masters of camouflage, able to change colour rapidly and texture of their skin to reflect the seabed they are on. Different camouflage is also use for communication, for example the display of zebra stripes act to attract a mate.

Gravels are also hugely important for fish spawning, which will create burrows/holes into the seabed ideal for laying and protecting eggs.

The male black bream seeks out gravel areas to create an up to 2m in diameter depressions in the surface using his tail, to form nests which the females will lay their eggs in.

Is it threatened?

The biggest threat to this habitat is aggregate dredging. Each year 20 million tons of sand and gravel is dredged from the seabed. Trawling methods such scallop dredging can also cause unrest for species settled on the seabed and species, such as bivalves and habitats such as biogenic reefs, are extremely sensitive to disturbance.