In the latest in our monthly series on habitats in the North Devon Biosphere we look at our rocky shores

WHY are North Devon's rocky shores some of the best habitats in the Biosphere Reserve and amongst the richest in the country for their marine life? Grand geology and wild waters provide some of the answers.

The Biosphere coastline stretches over 77 miles from Welcombe in the south, with its stunning stratified rocks, to Foreland Point and the towering cliffs of Exmoor in the north.

Its mix of shore habitats includes the golden beaches that are so beloved by holiday-makers but that are, from the point of view of marine life, virtual deserts by comparison to our rocky shores.

Rocks may seem inhospitable, but they provide an anchorage for many encrusting plants and animals, like seaweeds, sponges and barnacles, as well as shelter in rock-pools and other nooks and crannies for mobile animals such as crabs and fish.

Rocks strike out into the full force of the waves at west-facing Hartland, and the headlands at Croyde and Woolacombe.

These are exposed shores, suited to the toughest animals and the firmly-attached that feed well in rich water.

They contrast with the more sheltered Channel coast shores beyond Morte where the animals are often softer-bodied and thrive in the siltier waters.

This range of exposure contributes to the biodiversity and conservation importance for which much of our coast has been designated.

The stretch from Combe Martin to Croyde is a Voluntary Marine Conservation Area, and Foreland Point to the Estuary mouth is a candidate for Marine Conservation Zone status, as is part of the Hartland Peninsula.

The shore's inhabitants have to adapt to make the most of a complicated jigsaw of factors influencing where they live.

As well as waves, our shores are subject to the Bristol Channel's powerful currents that ensure that our waters are rich in food and can sustain large numbers of marine animals, but perhaps the greatest challenge for marine life is this area's huge tidal range; the second highest in the UK.

Simply staying wet enough to breathe poses problems but then there are the other necessities of life such as eating and avoiding being eaten, sex and reproduction and competition.

Rocks might look bare, but this is only because the microscopic seaweeds that coat them are being grazed by limpets and other sea snails before the weed has a chance to grow.

Mature limpets have a neat trick that enables them to live on the drier parts of the shore.

As the tide recedes, they retrace their route and hunker down on a home scar, an indentation that they have tailored for a snug fit where they can keep moist.

When the tide is out other animals that can withstand considerable fluctuations in temperature and salinity can be found in the rock-pools.

Here throughout the day snails graze, mussels and sponges filter water for food, anemones grab passing prey, and small fish and crabs feed, alert for predators.

Many animals have evolved adaptations that help them cope with the ever-changing conditions in the rock pools by sheltering and waiting for the sea to return.

For example, sea-snails have trap doors that shut in a little moisture whilst blennies can hide in shady crevices and breathe through their moist skin. The beadlet anemone can close its tentacles and shelter under a protective coat of mucus

Coastwise North Devon's shore safari organiser, Jim Monroe says: "Understanding how these animals behave helps you to find them. Each has their place on the shore where their chances of survival are best.

"Find a good rock-pool and you can watch them close at hand. Many are indifferent to your presence, others may eye you warily, but most will continue about their business. To see them feels like a huge privilege."

When covered by the tide barnacles and mussels, animals that dominate the exposed shore, come to life.

Barnacle larvae that have glued themselves to the rocks headfirst when settling as adults, constantly sieve the water for food using their feathery legs, stopping only when a threat looms, such as a young blenny looking for a leggy meal.

Carpets of mussels open to syphon and filter gallons of water for food. Like barnacles they are prey to the dog whelk, which can take a week to drill into a mussel and make a soup of it.

The mussel has a surprising defence and can trap the whelk using the threads with which it anchors itself to the rock.

Further down, shore encrusting colonial animals join seaweeds to give a colourful patchwork coating on most surfaces.

They provide micro-habitats with good feeding for many small animals including the cowrie which feeds only on star ascidian, in a food chain that runs from microscopic plant and animal material in the plankton to top predators such as seals and dolphins.

Coastwise member Paula Ferris says: "For me the low shore is the most exciting part to explore. It is wetter for longer so there are more animals.

"Blennies and other shore fish lurk under the weed, crabs tuck into crevices, and every large stone hides tiny scuttling Porcelain crabs and maybe brittlestars or sea urchins.

"Better still I might find a worm pipefish, a sea slug, or even a squat lobster clumsily backing-off as I draw back the weed. There will always be something new for me, such is the variety of life on our rocky shores."

Learn more about the Biosphere at www.northdevonbiosphere.org.uk or www.coastwisenorthdevon.org.uk