Sea mat

Sea mat

Sea mat ©Jessica M Winder

Sea mat

Scientific name: Membranipora membranacea and Electra pilosa
These mat like growths found on kelp and seaweed are actually colonies of tiny individuals animals.

Species information


Sea mats vary in size, from a few cm across to covering whole seaweed fronds.

Conservation status


When to see

January to December


Have you ever spotted a lacy mesh-like growth on seaweed whilst rockpooling and wondered what it was? These patches are called sea mats and can cover huge sections of the fronds of kelp and seaweed on rocky shores. Sea mats are a colony of individual animals called zooids. If you look closely, you'll see what look a bit like cells - these individual little boxes are each home to one zooid. The zooids filter feed on phytoplankton using special feeding tentacles called a lophophore. They can reproduce asexually to increase the size of the colony - which can grow by several millimetres a day! The name for these colonies is "Bryozoan", a large and diverse array of colonial creatures known as Sea Mosses.

How to identify

A lacy mesh-like growth found on the fronds of seaweeds on the rocky shore, mainly on oarweed (kelp) and on serrated wrack. There are 2 main species of sea mat on UK rocky shores, you can tell them apart by the shape of the zooid boxes. Membranipora membranacea has rectangular boxes whilst Electra pilosa has oval boxes and tall spines giving it a hairy appearance.


Found around all UK coasts.

Did you know?

Sea mats are a favourite food of nudibranchs. Look closely and you might well find one of these colourful little sea slugs munching away.

How people can help

When rockpooling, be careful to leave everything as you found it - replace any rocks you turn over, put back any crabs or fish and ensure not to scrape anything off its rocky home. If you want to learn more about our rockpool life, Wildlife Trusts around the UK run rockpool safaris and offer Shoresearch training - teaching you to survey your local rocky shore. The data collected is then used to protect our coasts and seas through better management or through the designation of Marine Protected Areas. The Wildlife Trusts are working with sea users, scientists, politicians and local people towards a vision of 'Living Seas', where marine wildlife thrives. Do your bit for our Living Seas by supporting your local Wildlife Trust or checking out our Action Pages.