Intertidal Sandflats and Mudflats

Intertidal sandflats and mudflats are sediment habitats that are uncovered by the tide. The animals and plants which are supported by a sand or mud flat vary according to the type of sediment, its stability and the salinity of the surrounding water. They tend to be exposed to low energy movement and higher levels of organic matter accumulate in these habitats, providing a rich source of food for animals living both in and on the sediment. Sand and mud flats are home to an abundance of marine life, including many marine worms such as the ragworm (Nereis virens).

Intertidal sand and mudflats are a designated interest feature of the Berwickshire and North Northumberland Coast SAC, the Tweed Estuary SAC and the Coquet to St Mary’s MCZ.

The muddy sediment areas around Lindisfarne support the largest beds of narrow-leaved (Zostera angustifolia) and dwarf seagrass (Zostera noltii) on the east coast of England. These beds and their associated communities of plants and animals are becoming increasingly rare and are an important foraging area for birds such as wigeon and light-bellied brent geese. In addition, seagrass is increasingly being recognised for the important role it can play in absorbing and storing Carbon dioxide from the atmosphere.

Cleaner, sheltered sands at Low Newton-by-the-sea support a rare intertidal population of the heart urchin (Echinocardium cordatum). This animal burrows in the sand, but is normally only found in the subtidal zone. Razor clams (Ensis ensis) can be found in vertical burrows in the sand, into which they descend rapidly when disturbed. Areas of clean sand normally occur in locations with high-energy water movement. The communities within this habitat tend to be less diverse than sheltered locations due to the mobility of the sediments. Small crustacean amphipods and robust marine worms, such as the lugworm (Arenicola marina), can exist in these conditions.

Mussel beds are present in certain sediment areas where small pebbles and shells provide some initial anchorage. Once established, these beds provide a sub-habitat for a host of other small plants and animals, which in turn are a rich food source for larger marine predators such as fish, birds, crustacea such as the shore crab (Carcinus maenas) and echinoderms such as the common starfish (Asterias rubens).