Natural England - Intertidal mud

Intertidal mud

Muddy seashores.

Intertidal mud © Paul Kay

Mudflats, which are covered by the sea at high tide and exposed as the tide goes out, are found in sheltered, coastal inlets, such as harbours and estuaries. They are created because the quiet water allows fine silts and clays to settle from the water onto the seabed. Rotted vegetation, transported to the sea by rivers and streams, is also part of the mudflat mix.

Mudflats might seem unpleasant, inhospitable areas of waste ground to us but they are teeming with life. The mud is rich in nutrients and is anything but barren.

The surface of the mudflats is home to shore crabs, shrimps and sea snails and a few seaweeds may grow on any piece of hard substrate – a pebble or an empty shell. However, it is the life within the mud that is amazing. Mudflats are home to vast numbers of worms, such as ragworms and lugworms, as well as cockles and other bivalves (with their paired, hinged shells).

Mudflats are hugely important, as they are the larders of the seashore world, providing food for breeding and wintering waterfowl and wading birds. These probe the mud for a tasty worm or cockle, as do the fish that use the areas when the tide comes in.

Many of our estuaries have European and international conservation designations, mainly to protect the birds, which are attracted there by the plentiful food supply within the mud.

Threats to our mudflats include bait-digging, reclamation, pollution and sea level rise.

Brief description of European distribution

Intertidal mudflats are widespread on the Atlantic coasts of Europe, particularly in the large estuaries feeding into the North Sea.