The Joy of Rockpooling

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The Wildlife Trusts’ National Marine Week runs from July 22nd to August 6th this year. Set up to celebrate the wealth of life found in our seas, the event actually runs for two weeks to take advantage of different tide times around the UK. From rockpooling to seaside walks, there are lots of events to take part in. As an island nation, the sea has always played a huge part in our culture and history, for good or ill. After all, wherever you are in the UK, you are never more than 70 miles from the sea.

Beadlet anemone
Beadlet anemones are a common rockpool species

The sea’s natural history, though, is also extremely important. For one thing, the sea is a vital carbon sink. And our waters support a diverse range of organisms, from large mammals such as fin and minke whales, to the microscopic planktonic organisms that support complex marine food webs. One of the easiest ways to start getting to grips with this diversity is to have a go at rockpooling along the intertidal zone. This wonderful pastime can turn up some truly incredible creatures. Have a look at some of my favourite finds below.

Rockpooling 101

There are a few things to remember when going rockpooling. First, a few safety points. ALWAYS check tide times before going out. As well as making sure you are there at the best time to see exposed pools, knowing tide times means you won’t get cut off and into danger. However tempting it is to go barefoot, wear shoes or sandals. Feet can get cut easily on sharp barnacles and the like. Aqua shoes are a great idea as they protect the feet and usually grip well. Rockpools are often surrounded by seaweed making them very slippery, so care is needed when moving around. If you are going out alone, always let someone know where you are and when you are due to leave, too. Finally, the sun can cause a lot of damage, even on dull days. Sun cream and a hat are therefore a must.

Underwater viewer rockpooling
Underwater viewers help you cut out glare and reflections

What about the rockpooling itself, though? Not all beaches have rockpools of course, so look for ones with a sheltered rocky area. On sunny days in particular, approach a pool with the sun in front of you. This means you won’t cast a shadow over the water and scare things into hiding. After looking for anything out in the open, gently turn over any stones in the pool to see what is underneath. Clear plastic food tubs, like the ones from takeaways, or jam jars are great for temporarily collecting anything you want to have a better look at. You can also buy or make a rockpool viewer. This lets you look in the water clearly without any glare interfering. Once you have taken pictures or noted your finds, ALWAYS put them back where you found them, and return any upturned stones to their original position.

Rockpool Favourites

Rockpool organisms are incredibly hardy. After all, they have to cope with a dramatic change in conditions twice a day. At high tide, pools are often completely submerged, giving inhabitants more space and the option to move between pools. At low tide, those that can’t live out of water are cut off from other pools and the wider sea. They are also subjected to more sunlight, heat and higher salinity as water evaporates. Let’s meet some of these specially adapted creatures.

Hermit Crab

The UK has a number of different hermit crab species. As its name suggests, the one you are most likely to find rockpooling is the common hermit crab. Unlike other crabs, hermit crabs don’t have a hard shell, or carapace. To protect their soft bodies, they use empty mollusc shells instead. They commonly use whelk and periwinkle shells. When hiding, they withdraw completely into the shell. As the crabs grow, instead of shedding their own carapace as other crabs do, they swap to a larger mollusc shell. Once hermit crabs reach full size, they often leave the protection of the rockpool and move to the seabed out in open water. When rockpooling, look for molluscs moving faster than expected to find your own.

Hermit crab rockpooling
This hermit crab has chosen a common periwinkle shell as home
Common hermit crab
Common Shore Crab

Also known as the green shore crab, these crustaceans have their own hard carapaces and don’t need to coopt anyone else’s! Not all shore crabs are green; orange and red individuals are also reasonably common. The largest animals can have shells ten centimetres wide. Like the hermit crab, it finds much of its food by scavenging, but it also eats seaweed and catches shellfish live. It is able to cope with high variations in water salinity. This makes it well adapted to the rocky shores and shallow waters it favours. The common shore crab is native to the north-east Atlantic but has been introduced to a number of other locations including the USA, South Africa and Australia. In many of these places it is now classed as highly invasive as it outcompetes and predates native species.

Common shore crab rockpooling
Unlike hermit crabs, shore crabs grow their own shells
Common Starfish

Common starfish are surely our most recognisable rockpool species, although they also live out in deeper waters. Sadly, many of us only come across the dried-up dead specimens washed up on the shoreline. This particular species of starfish has five arms and is usually orange in colour. They might not look like it, but they are voracious predators. Their strong arms are able to pull apart bivalve shells like mussels, clams and oysters. Starfish then have a fascinating method of eating their prey. Amazingly, once they have opened a shell, they extend their stomachs out of their mouths and into the shell cavity. They then use digestive juices to partly break down the mollusc’s soft body before reabsorbing it all. Yum! They are also able to regrow missing limbs. Look out for their smaller relative the cushion star, too.

Common starfish
Starfish use their strong arms to prise open shells
Brittle Stars

These long-limbed relatives of starfish are more delicate, with their arms breaking off much more easily. Although they are also able to regenerate their limbs, it is better not to touch these fragile creatures. They use their arms to move sinuously across the seabed or the bottom of rockpools. A few similar species live around the UK including the common brittle star, crevice brittle star and small brittle star. Because they are vulnerable to predation by their larger starfish relatives, they often hide in cracks and under stones in rockpools. As well as rockpools, they are found in a range of marine habitats and can sometimes form large, mobile beds where there is lots of food. Different species feed in different ways. Some are scavengers while others eat particles of food or plankton suspended in the surrounding water.

Brittle stars use their long limbs to move around
Beadlet Anemone

One of our commonest sea anemones, the beadlet anemone is usually a dark red colour. The main part of the body is a fairly simple structure consisting of a dual mouth and anus cavity surrounded by nearly 200 stinging tentacles. These are extended when the anemone is submerged in order to feel for and catch prey. At low tide, the tentacles are withdrawn into the body, making them look like blobs of red jelly on the rocks. At the bottom of the body is a sucker which attaches the animal firmly to the rocks. Beadlet anemones can actually move slowly across the rocks. However, doing this means they risk attack by neighbouring anemones as they are highly territorial. The blue dots you might see just below the tentacles contain lots more stinging cells used purely to fight off encroaching anemones.

Beadlet anemones rockpooling
The blue dots visible on these anemones contain stinging cells used to deal with encroaching neighbours
Beadlet anemones
At low tide, anemones resemble blobs of jelly
Common and Flat Periwinkles

These two molluscs are very common on rocky shores throughout the UK. Common, or edible, periwinkles are the larger of the two, with a whorled shell up to five centimetres high. They are usually grey or brown in colour. At low tide, they often clump together in large aggregations in places they can stay as wet as possible. When submerged, they can be watched grazing algae on rocks and barnacles, looking for all the world like a herd of tiny sheep or cows. Flat periwinkles, meanwhile, come in a huge variety of colours, including bright yellow, brown stripes, red, orange and green. Much smaller, they are approximately one centimetre across. There are actually two extremely similar species in the UK. They eat seaweed and can often be found attached to the undersides of fronds.

This common periwinkle is grazing algae
Flat periwinkles rockpooling
This picture shows the range of colours flat periwinkles come in
Common Limpet

This marine mollusc has an instantly recognisable conical shell and grows to about six centimetres in diameter. They are generally a grey colour unlike some of the more brightly coloured limpet species found around our coasts. At high tide, limpets move around the rocks grazing on algae. To feed, they use a structure called a radula, which is the mollusc equivalent of a tongue. However, this ‘tongue’ has hundreds of tiny teeth covering it. These teeth help limpets scrape algae off the rocks easily and make the radula an extremely tough piece of kit. When the tide is out, limpets leave off grazing and return to the exact same spot each time. Here, they attach themselves firmly to the rocks to avoid drying out. In fact, they stick so firmly that over time they leave an impression on the rock called a ‘home scar’. Don’t ever try and pull a limpet off the rocks as you can easily damage the muscle used to hold it in place.

Limpets rockpooling
Limpets at low tide

Chitons (pronounced ‘kite-ons’) resemble legless woodlice or pill bugs with their eight interlocking plates and ability to roll into a protective ball when knocked off the rocks. They are, however, molluscs that behave in a similar way to limpets. Like their larger relatives, they use a toughened radula to remove algae from the rocks. They also attach themselves firmly when the tide is out to protect their soft bodies from drying out. We have approximately 15 species in the UK, and they can be quite hard to tell apart. Their subtly coloured markings camouflage them well against the rocks. Most are only about two centimetres in length, although some reach lengths of four centimetres. Incredibly, they have been around in one form or another for at least 300 million years, suggesting they are very well adapted to their chosen environment.

Eight interlocking plates make up a chiton’s shell, visible here

A number of very similar barnacles live on the rocks around the UK so for the purposes of this article, I’m going to lump them together. Although they look like molluscs, barnacles are actually crustaceans, related to crabs and lobsters. They sometimes collect in huge numbers across the surface of rocks, as well as piers, sea walls, boats and even whales. As larvae, they swim about looking for somewhere suitable to settle. Once in adult form, armoured plates protect the soft body inside. A glue-like substance fixes them firmly to the surface they have chosen to stay on for the rest of their lives. Barnacles are filter feeders, using comb-like structures called cirri to catch passing food particles when submerged. When exposed, they are able to close plates at the top of the body to prevent drying out.

This footage shows barnacles feeding with their comb-like cirri
At low tide, barnacles avoid drying out by closing door-like plates in their outer structures

Also known as the common blenny, this fish is a real rockpool and shallow water specialist. A key adaptation is their ability to survive for a certain amount of time out of the water. They are able to do this because of a coating of slime that helps them stay damp when exposed. Despite being fairly common, the shanny is quite difficult to see. This is partly because its mottled brown or green colouring camouflages it beautifully against rocks and seaweed. It is also shy, moving quickly to hide when it detects danger. Look for a quick moving little fish with a long body and wide head. They have a varied diet, using their sharp teeth to eat barnacles, seaweed, worms and all sorts of other marine organisms.

Shannies use a protective slime to survive out of water

Rollicking Rockpools

These are, of course, just a fraction of the wonderful range of organisms that make their living in rockpools. There are lots more things to look out for when rockpooling, including whelks, sea slaters and a whole range of seaweeds (look out for a future post on these algae species). Have you seen anything out rockpooling? Let me know in the comments below!

A flat periwinkle in motion

Please note that everything in these pictures was quickly returned to where it was found.

Further Reading

To join in the celebrations for National Marine Week, have a look at the Wildlife Trusts’ website for events and ideas on how to take part.

Heather Buttivant’s beautiful book is a wonderful introduction to the world of rockpooling. Buttivant’s passion for her subject shines through as she introduces 24 of her favourite rockpool inhabitants. She also shows just what makes rockpools so fascinating.

Nicolson’s book similarly explores the wonders of the shoreline but also delves into human elements of this ever-changing habitat. Along the way, he reveals some amazing facts about some of the creatures that make their livings between two worlds.

To get to grips with identifying your rockpool finds, this book is one of the best general guides to coastal wildlife. Many of the species found in rockpools are included here in a jam-packed photographic guide.

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