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Nature in Shetland

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Shetland Biological Records Centre

 

 

Rocky Shore Animals

Because of its northern location and the warming influence of the Gulf Stream, Shetland is a mixing pot for marine life. Sea temperature is one of the main factors influencing the distribution of marine animals around Shetland. For some that prefer colder, Arctic waters, Shetland is the furthest south that they reach, whilst others from warmer waters reach their northern limit here.

The climate in Shetland is changing and some people feel that this may be accelerated as a result of global warming. This is expected to affect the coastal environment through increasing seawater temperature, rising sea levels and increased storminess. As a result there will be changes in populations of some marine animals around our shores. The animals described in this leaflet are ones whose distributions are expected to alter if our climate changes. Some may become much more common in Shetland, while others may disappear from the islands altogether.

Shetland Biological Records Centre is keen to find out more about Shetlandís marine life and whether we are beginning to see the changes in distribution of some rocky shore animals that are expected as a result of climate change.

Please help us to do this by recording your sightings on the recording form and returning it to SBRC.

The animals described in this leaflet can all be found on rocky shores. Some like living in rock pools, others under boulders, and some simply spend most of their lives stuck onto rocks

Divisions on the Shore

The rise and fall of seawater with the tide has a big influence on rocky shore animals. Some prefer to live close to the low water mark where they spend most of their day underwater. Others live in the middle of the shore spending roughly equal amounts of time underwater and in the air. Animals which live on the upper shore are only covered by seawater at high tide. This pattern is called ZONATION. Look at the zonation diagram next to each animal to find out where on the shore youíll be most likely to see it.

Tortoiseshell Limpet Tectura testudinalis

Tortoiseshell limpets can grow up to 3cm across -noticeably smaller than most other limpets which you see around Shetland. The background colour of the shell can range from white to grey to pale green, and its surface is very smooth  compared with other limpets. The feature that gives this limpet its name and makes it stand out from all the others, is the dark brown stripes which run from the tip right down to the edge of the shell. They can be found on boulders or small smooth stones, particularly those with pink crusts growing on them.

Pearly Topshell Margarites helicinus

Topshells are a group of small marine snails. The shell of the pearly topshell is only about 3mm tall  -  smaller than a pea! Its colour varies  from an orange-red to cream-brown, patterned with green or purple. Have a look for these topshells under stones or attached to seaweed on the lower shore, as well as in rock pools.

Star Barnacles Chthamalus stellatus

Although barnacles look like molluscs (seashells) they are actually more closely related to crabs and lobsters. If you watch barnacles under water - at the edge of a rock pool for example - you will see that they have tiny hairy legs which stick out through the opening in the middle of  the shell. They wave their legs about in the  water to catch their food.

There are many  different types of barnacles on the shore. The number of plates that form the protective shell will help you to tell the different types apart. Star barnacles have six roughly equally sized plates. The shape of the opening is also distinctive - star barnacles have oval shaped openings whereas many other types of barnacles have diamond or kite shaped openings. Have a careful look at the pictures below and this should help you to tell the difference between the star barnacles and the others. Star barnacles are found much higher up the shore than all of the other animals in this survey sheet.

Snakelocks Anemone Anemonia viridis

Snakelocks anemones can have up to 200 long tentacles which are usually green with bright purple tips. They are called snakelocks because the tentacles can look like a mass of tiny snakes. Unlike many anemones (such as the beadlet anemone, which can often be seen on the shore looking like a blob of red jelly) snakelocks anenomes rarely pull in their tentacles. They can be found attached to stones and rocks on the  lower shore and in rock pools.

 
Shore Crab Carcinus maenas                 
Edible Crab Cancer pagurus

Look carefully at the pictures - can you tell the difference between these two crabs? The one on the left is a shore crab. It has five teeth on each side of its carapace (shell) as well as three bumps between its eyes. The one on the right is an edible crab and the edge of its carapace resembles a pie crust. The shore crab is also a much darker colour, usually dark green, whereas edible crabs are reddish brown.

The bars marked on the pictures above show where to measure the width of the carapace of the two different types of crabs. To work out the size of any edible crabs that you find simply measure the widest part of the carapace. On shore crabs, measure the width of the carapace between the last of the five teeth on each side. When measuring the crabs be careful that they donít nip you. As crabs grow they periodically shed their old carapace and their new carapace takes a while to harden. If you find any soft crabs be careful not to squash them!

Shore crabs can be found on all types of shores, particularly among seaweed. Edible crabs live mainly in holes and crevices between rocks. Adults spend much of their life underwater but young edible crabs can be found under boulders and stones on the lower shore. Donít be surprised if all of the crabs that you find on the shore are fairly small.

Please send your records to : SBRC, Shetland Amenity Trust, Garthspool, Lerwick, Shetland. Tel. (01595) 694688.

 

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