Summer by the pool: Where keen rockpoolers should cast their nets

August's low tides bring a chance to see sea anemones, crabs and even starfish up close

Nothing transports you back to childhood quite as much as rockpooling. There's that bewitching combination of sun, sea, sand and secrecy – plus all the salt-laden air helps you work up an appetite for great British seaside staples such as mint choc chip ice cream and chips. The seashore is a fascinating environment – the ebb and flow of the tide reveals places and creatures normally hidden from our gaze and leading mysterious little lives.

Most of the UK's coast has two high and two low tides every 24 hours; the highest tides are in March and September when the sea retreats much further and you can see species you wouldn't normally have an opportunity to spot, such as sea urchins and sea squirts. August is a fine time to ferret around, too – and it's National Marine Week from 2 to 17 August.

"There's lots more of everything in summer," says Tom Hardy, Cornwall's Wildlife Trust marine conservation officer, "Sea slugs are one exciting species you might see in summer. Due to the warmer water there's more seaweed along the shoreline and they come in to feed on these different types of algae."

Lisa Chilton, The Wildlife Trusts' marine development manager, says, "The UK's 11,073 miles of coastline is host to an amazing array of wildlife, including corals, whales and dolphins, basking sharks, seals, and myriad fascinating fish, crustaceans and molluscs. We want people to get out there and discover the secrets of our seas."

How to rockpool

It's a good idea to wear wellies; kids – take an adult with you – and always check the tide times. If you've got any scratches, cover them with waterproof plasters. You'll need a white tray (I use the ones for developing photographs) or bucket, a net, a seashore identification guide, a magnifying glass and maybe some clear jars. Choose a pool that's small enough for you to reach into without standing in it and try not to cast your shadow across it or you'll scare everything away. Just look first – once you put your hand in, most animals will hide. Fill your tray with water from the pool and pop anything you catch into it. Many smaller species can be safely picked out by hand, if you're gentle. Hermit crabs and snails such as winkles and whelks may even come out of their shells if left alone.

Use the net to scoop up anything speedy like prawns and fish and then let them swim out of the net into the tray. By putting creatures into jars you'll get a chance to see them up close. Some animals like hiding in seaweed so have a good search after you've got everything obvious – but don't pry creatures out of their hiding places or remove animals that are stuck to rocks. And when you're done, put everything back.

What to look for

Sea anemones

The commonest is the beadlet anemone, Actinia equina, which is found in two morphs, one is a deep port red and the other is dark blue-green. When their tentacles are retracted they look like candied blobs; the red kind has bright blue spots in a ring around its mouth. The dahlia anemone, Tealia felina, is magnificent. It has 80 translucent, banded tentacles but can be hard to see when they are retracted as sand and shells stick to its warty skin.

Shellfish

Limpets, Patella vulgata, with their conical shells, are the most abundant. They use their large muscular foot to stick closely to the rock and will always return to the same site. They use their rasping tongue, called a radula, to scrape algae off the rocks.

Top shells are also beautiful and widespread. They're conical and lined with mother-of-pearl. The creatures inside browse on algae. They show zonation, with different species living at different parts of the shore. For instance, the purple topshell, Gibbula umbilicalis, which is grey with purple lines, is found around the mid-tide level, whereas the painted topshell, Calliostoma zizyphinum, lives at extreme low water sites.

Fish

One exciting fish find is the lumpsucker (Cyclopterus lumpus). It's a grey-blue, scaleless, somewhat flabby fish, up to 30cm long with a large sucker that it uses to attach itself to rocks. The eggs can be sold as caviar. They're solitary fish, but in January the males start defending territories. Once they've persuaded females to lay eggs for them to fertilise, they'll guard their clutch.

One of my most interesting finds was a pipefish, Nerophis lumbriciformis. They're whippet-thin and sea horse like. They grow to about 15cm long and have tiny dorsal fins and a narrow snout. As they're dark olive they're well camouflaged among the seaweed.

Seaweed

Coralweed, Corallina officinalis, looks like a pale pink coral but is a red alga. It grows between two and 12cm high and has a flattened branched structure. It accumulates lime, which is what makes the plant stiff.

Crabs

The most striking crab you'll find is the velvet swimming crab, Macropipus puber. It's feisty and will try its best to nip you if you pick it up. It has a blue carapace, up to 8cm across, and blue lines down its legs. It's covered with soft, maroon-coloured hairs, which give it a velvety appearance and it has bright red eyes.

Starfish

The common starfish, Asterias rubens, found in large numbers wherever there are mussel beds. It prizes open these shellfish with its suckered feet. It has five fat arms and grows to 12cm across in rockpools but can reach almost half a metre in deeper waters. It's a dull apricot with white spines.

What to avoid

Be careful picking up crabs as they can give you a nip. Avoid touching the snakelocks anemone, Anemonia sulcata. Its beautiful tentacles are green with violet tips but can sting. Some jellyfish can also sting and can be stranded when the tide goes out. The compass jellyfish, Chrysaora hysoscella, cream with brown patches and a brown-edged bell, has four frilly tentacles that you should avoid. The violet-blue Cyanea lamarckii and our largest British jellyfish, Rhizostoma pulmo, which can grow up to 60cm across and has an apple-green bell, can also give a nasty sting.

The best places to go

Helford Passage in Cornwall is my favourite place to go rockpooling and has a rich abundance of sea life. Offshore there are beds of maerl, a rare seaweed. There are beds of eelgrass, the only British flowering plant that grows in the sea, which provides shelter for sea hares and sea lemons. Plus, there are 80 species of fish in the river. The mudflats support invertebrates such as the peacock worm, Sabella pavonina. See www.helfordmarineconservation.co.uk for details of events.

Broadcaster Bill Oddie says Kimmeridge in Dorset is the UK's best rockpooling site. The bay has a double-low tide, which will give you more than three hours to explore the shore. Smooth rock ledges reach far out into the bay, allowing easy viewing of marine life. The clear, shallow water is an ideal habitat for a multitude of rockpool creatures from anemones to sea slugs, as well as nurseries for juvenile fish.

Wembury in South Devon is famed for its fantastic rockpooling. You can find at least eight types of crab, as well as spiny starfish, squat lobsters, and fish such as blennies, gobies and rockling. Wembury Marine Centre runs "rockpool rambles", see www.wembury marinecentre.org. Dunseverick Harbour (near Portrush, Co Antrim, Northern Ireland) has the deepest natural pools in Northern Ireland, with an extraordinary range of marine wildlife, including the sea hare, china limpet and needle whelk. Rathlin Island nearby is home to sponges found nowhere else in the world.

Killiedraught Bay, within the St Abbs and Eyemouth Voluntary Marine Reserve in Berwickshire, is one of the finest rockpooling sites in Scotland. You could find animals such as the breadcrumb sponge, bootlace worm and butterfish. The cliffs at St Abbs Head host 50,000 seabirds in spring and summer, such as guillemots, razorbills, kittiwakes and shags.

Visit www.wildlifetrusts.org/marineweek to find an event near you.

Sanjida O'Connell presents 'Nature's Top 40' on BBC2, a guide to our best British wildlife spectacles, later on this summer