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
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
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
Star Barnacles Chthamalus
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
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
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
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.
your records to :
SBRC, Shetland Amenity Trust, Garthspool,
Lerwick, Shetland. Tel. (01595) 694688.