Crabs and snails, barnacles and blobs!

 

APRIL/MAY 2021

A regular column from BEACHstuff.uk, the Ilfracombe-based online guide to everything we find on UK Beaches.

 

North Devon has excellent rockpooling beaches. Our rocky coasts and Devonian slate make for plentiful nooks and crannies in which sea creatures find safety when the tide is out. And many are accessible to curious humans!

 

These are just some of the more common creatures which can be seen here in Ilfracombe at this time of year. In future issues of Focus, we'll look at more and more creatures and some of the more exotic visitors.

  BARNACLES  

 

The most numerous rockpool inhabitant is one that we hardly even notice is there. Our dark grey slate rocks often look white because they are covered in hundreds of thousands of the tiny white homes of barnacles, a relative of shrimps. 

 

These tiny creatures build their conical shells - often only 2 or 3mm tall - with a trap door at the top. When the tide is out the trap door stays firmly shut to protect the barnacle from predators and the drying effects of the sun. But when the tide is in, it is time to eat! The barnacle, lying on its back in its shell, waves it many legs around in the water to catch little bits of food passing by.

The legs of a barnacle feeding underwater. And below, a stack of them waving their legs about.

  LIMPETS  

 

Often seen amongst the barnacles are much bigger conical shells, rising to a point - the shells of limpets. Limpets are, in fact, snails, related to the garden snails we all know. They are specially adapted, however, with thick shells to withstand the beating of waves and a a broad base, to allow it to hold fast on the rocks so that even the sharp beaks of herring gulls can't pull them off. 

 

 

Limpets are incredible snails that we don't yet fully understand. Living to an impressive 10 to 15 years old, they pick their spot on the rock and, while they wander off foraging for algae when the tide is in, they are always able to find their way back to their home spot. There are many theories as to how they are able to find their way home, but we don't yet know for sure. Recently, it was discovered that their tiny teeth are actually made of the hardest substance ever known - either in nature or man-made.


Because limpets are so dependent on being able to get back to their home spot, it is really important never to move them from their place on the rock.

 

The underside of a limpet. You can see its large foot  - with which it moves on the rocks - and, above it, the tiny mouth.

  SHORE CRABS  

 

Several species of crabs are common on North Devon coasts - which we will introduce in future issues of Focus - but the one you are most likely to see alive is the Shore Crab as it tends to be found higher up the beach, especially when they are young and tiny. 

It often has a greenish hue but can also be brown, black - I have even seen a bright blue one! Crabs moult regularly and slip out of their old hard shell (known as a carapace) when their bodies have grown. You can often see washed up discarded shells on the beach - not a dead crab, but an empty shell.

  DOG WHELKS  

 

Most sea snails like the limpets (above) are vegetarian - feeding on algae that grows in green patches on the rocks, but dog whelks are true carnivores! Dog whelks are particularly partial to eating other snails.

 

They have a fearsome tongue which they use to drill through the shells of other snails - mussels are a favourite. They then suck out the hapless little snail body through the hole. They are also known to travel over barnacles, nipping off their little legs.

 

 

   BEADLET ANEMONES   

 

There are several species of anemone to be found in Ilfracombe but the most common is the beadlet anemone. When the tide is out, their fat little blob bodies can be seen motionless stuck on the rocks.

A beadlet anenome in the water with its tentacles out. The  blue dots are its fighting cells, with which it will sting opponents - in this photo a stone has rolled too close.

 

They come in all shades of dark brown through to bright red. And there are even green ones. When they are in water - in a rockpool or when the tide comes in - their tentacles come out and they start fishing, catching bits of food, small fish and whatever else they can find on their sticky tentacles. They then pop the food into their mouths (in the centre of their tentacles). As they use the same hole as both mouth and bottom, there is enormous potential for confusion...

 

 

For more on all of these creatures - and many many more! - head to beachstuff.uk