What is a chalk reef?

A reef is a ridge, ledge or outcrop that sticks out of the surrounding sea bed. 

You might hear ‘reef’ and think ‘coral’, but reefs can be made from anything, and here in Sussex many are made of chalk.

Reefs tend to support high levels of biodiversity, because they provide a stable surface that animals and algae can hold on to. Once these species anchor themselves to the sea bed, they attract more mobile species to move into the area, in search of food, shelter or a mate.

Rocky reefs are formed by erosion – you can see how our East Sussex coastal chalk cliffs have been eroded over time, forming what's known as a wave-cut platform that is exposed at low tide.

This chalk system extends a long way offshore, meaning we have both intertidal (sometimes underwater) and subtidal (always underwater) chalk reefs.

Why is chalk important?

Although we have a lot of chalk in Sussex, on a wider scale it’s pretty rare. 

Chalk forms less than 1% of Britain’s coastline. More than half of that is in Sussex and Kent. 

Internationally, coastal chalk is even more scarce, with most of it in north-west Europe. England holds a globally significant proportion of all the world's marine chalk, meaning we have a special responsibility to protect it.

Both intertidal and subtidal chalk are classified as 'habitats of principle importance' in England, within section 41 of the Natural Environment and Rural Communities (NERC) Act 2006.

What lives on chalk reefs? 

Chalk is a famously soft kind of rock, and it attracts specialist rock-boring animals such as piddocks, spionid worms and the Boring Sponge. 

These specialists are habitat engineers, which change the physical environment around them. They create all manner of cracks and crevices, which in turn creates complex habitats for many other creatures, such as Tompot Blennies and Short-snouted Seahorses. 

You don’t need to look hard in a chalk reef to find a creature making use of a hole that’s been excavated by a Piddock.

Where are the chalk reefs in Sussex?

Intertidal chalk reefs can be found anywhere where there are chalk cliffs, mainly between Brighton to Eastbourne. This means that when the tide is low the chalk reef is exposed.

These areas make great places to explore on foot - see our Rock pooling Guide for tips on how to enjoy this environment safely.

Further offshore, chalk reef runs in patches from Brighton to Shoreham, with further outcrops in the Kingmere Marine Conservation Zone (south of Littlehampton and Worthing). 

Threats to chalk reefs

Though a protected habitat, chalk reefs remain at risk from various human activities.

Over a third of coastal chalk in Sussex has been modified by coastal defences and other forms of engineering work. 

This often damages the biodiversity of chalk reefs, as does toxic contamination and the physical loss of areas of chalk altogether. 

Invasive non-native species are also a threat, when they displace native wildlife. Pacific Oysters and Wireweed are becoming a problem here in Sussex.

How to help

There are many ways you can help to protect chalk reefs and the wider marine environment. 

Join Shoresearch - the volunteer scheme to identify and record animals, plants and habitats along our shoreline

Join Seasearch - the project for volunteer divers and snorkelers

Join a beach clean - regular volunteer events across Sussex