intertidal

Imagine walking along the beach at low tide. The strip of shore that the sea covers at high tide and leaves open at low tide is called intertidal. The word usually describes places, plants, animals, or habitats in that band between the high- and low-tide marks. It is a changeable place, regularly underwater and then exposed again as the tide moves in and out. You might hear about intertidal rocks, intertidal pools, or intertidal species when people talk about marine life along the coast.

Intertidal describes the part of the shore that lies between the high-tide line and the low-tide line, or the living things and conditions connected with that part of the shore. An intertidal area is underwater when the tide is high and exposed to the air when the tide is low, so it is a place of constant change where land and sea meet. You will often see the word in phrases such as intertidal zone, intertidal habitat, intertidal mudflats, or intertidal species.

This environment can be hard on life. Waves strike the shore, salt dries on exposed surfaces, temperatures shift, and animals and plants must survive both underwater and in open air. Barnacles, mussels, crabs, sea stars, and seaweed are common examples of organisms that may live in intertidal places. Scientists often divide this coastal band into upper, middle, and lower parts because each part has different conditions and different forms of life.

The word is most common in biology, ecology, and geography, but it also appears in nature writing and travel writing when someone is describing a coast. In everyday use, it helps name that narrow world that is never fully land and never fully sea, always changing with the rhythm of the tides.