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24 September 2014
Inside Out: Surprising Stories, Familiar Places

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  Inside Out - South: Monday June 30, 2003


Hermit Crabs -  copyright Colin Froud  -  Divercol Productions
Hermit crabs have an intriguing life cycle

If you thought rock pooling was a pastime only enjoyed by children, think again. Inside Out joins Marine Biologist Lisa Browning as she explores the diverse marine life in the rock pools of Kimmeridge Bay in Dorset.

As the tide recedes, not all of the coast is left behind dry and with a keen eye and a bit of patience, rock pools can reveal a wealth of sea life.

Rock pools offer better survival chances for animals and plants that need to be submerged all the time.

Deep rock pools provide shelter from waves, allowing fragile organisms to live on an otherwise exposed rocky shore.

Rock pools however are not always a safe haven.

Hidden danger

Lisa Browning
Marine Biologist, Lisa Browning explores the hidden wonders of rock pools

Snails that are able to survive in between high and low tide may find shelter in a rock pool - but so do their predators!

Large fish may find the rock pools too small, lacking oxygen for breathing.

Rock pools may also collect unwanted fresh water during rain storms. This is worse for shallow rock pools high up the shore where organisms must wait longer for the tide to return.

There may be hidden dangers in rock pools, but for sea creatures in need of water, they are vital for survival.

Magical world revealed

Rock pools provide a life-line for sea creatures and a unique opportunity to observe them without having to get your feet wet!


Hermit crabs are crustaceans (crusty-shelled animals that live in the sea)

Hermit crabs have a soft abdomen and they need to protect this soft part with an empty snail shell. As they grow, they have to search out larger snail shells

The two claws of hermit crabs are different sizes. Each species of hermit crab has the largest claw on the right or left

Most hermit crabs live in the sea, but there are a few species that spend almost the whole of their life on land

Land hermit crabs must return to the sea to breed. The female crab discharges her eggs into the sea. Larvae develop in the sea before they change into miniature hermit crabs, find a shell to protect them, and clamber out on to the land

Hermit crabs, like all crustaceans and insects, must shell their exoskeleton (the armoured covering their claws and front part of their body) in order to grow. The new larger exoskeleton grows underneath and needs to time to harden and protect them. This process is called "moulting"

When the tide goes out rock pools reveal a magical world of plants and animals.

Although only a stone's throw from dry land these pools are home to creatures from a different world. But to study them at close quaters - the answer may lie a little closer to home.

Dorset Wildlife Trust has discovered a revolutionary way of recycling detergent tablet nets to benefit eco-friendly crabbing.

The charity is appealing for people to send in detergent tablet nets to be used at the DWT Purbeck Marine Wildlife Reserve, at Kimmeridge Bay, enabling young children to enjoy crabbing during the summer.

The rock pools are bustling with crabs. You could spot the nimble shore crab, the hairy crab or the delicate porcelain crab and of course the hermit crab famous for stealing a shell for it's home.

"It is intriguing to see how effectively detergent nets can catch crabs, syas Dan Williams, Dorset Wildlife Trust Marine Warden.

The net is used to replace the hook, which as Dan explains, is good news for all.

"Bait is put into the net which the crab then grips with its claws. When a hook is used, fish can accidentally be caught and unnecessarily harmed.

"The hook can also be lost and injure other creatures, such as swans, as well as people's fingers!"

Home sweet home

Many small fishes use the rock pool as a shelter against the low tide. As soon as the new tide moves in, they leave the pool to wander around much larger territories where they find their daily food.

Goose barnacles - copyright Colin Froud  -  Divercol Productions
Goose barnacles were once thought to be young geese waiting to hatch

Research has shown that most of these small fishes stay in the same pool all their lives.

It is not only fish that make rock pools their home.

Worms of all shapes and sizes creep along the sea bed.

The candy striped flatworm is propelled by thousands of tiny hairs on its underside.

Goose Barnacles were once thought to be young geese waiting to hatch. In the middle Ages the Goose Barnacle was therefore classed as fish rather than fowl and could be eaten on Friday!

Rock pools are home to a wealth of interesting and diverse sea life and provides adults and children alike the unique opportunity to study it at close quaters.

But be warned - the best sort of rock pooling means leaving no trace of your visit. Always return creatures back to the sea and leave the wonders of the rock pool for all to enjoy.

See also ...

On the rest of Inside Out
Kimmeridge Bay

On the rest of the web
Dorset Wildlife Trust
Hampshire & Isle of Wight Wildlife Trust
Kent Wildlife Trust
South East Marine Programme
Sussex Wildlife Trust

The BBC is not responsible for the content of external websites

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