Although you may not know it, you almost certainly use seaweeds in your everyday life.
Extracts from seaweeds are used in many products, including in shampoo, toothpaste, cosmetics and medicines, and in foods.
Seaweeds are at the base of the marine food chain. Like plants on land, they photosynthesise, turning the sun's energy into food and removing carbon dioxide from the air.
Many different kinds of animals rely on seaweeds for food and the shelter that they provide.
Seaweeds are simple plant-like organisms. They live on seashores and in the shallow waters of seas throughout the world. 'Seaweed' is the collective name for a number of different groups of large algae that live in marine environments.
Even though 2 species may both be called seaweeds, this does not mean they are closely related to one another, as there are many hundreds of species in the UK alone.
Most seaweeds belong to either red, brown or green algae, and it is these groups that the Big Seaweed Survey is investigating.
Help us find out more about these wonderful organisms by taking part in the Big Seaweed Search. You don't need to be an expert - just use our downloadable guides.
Last year nearly 100,000 specimens were loaned to scientific institutions and researchers worldwide.