Inside a Shetland Rockpool

Rockpooling can be a fun activity to for the young, and not so young alike. There is a huge variety of species in this very changeable habitat. Many species have developed special adaptations to allow them to live in this harsh landscape, with changing sea levels, water temperature, salinity levels and the battering of waves. Read on to find out more about some of the most common species you are likely to see in a Shetland rockpool.

Just remember, if you plan on taking a trip to the coast, check the tide times first and be mindful of the rising tide. Do not go alone and always carry a mobile phone, if you find yourself in trouble call 999 and ask for the coastguard.

Green Shore Crab (Carcinus maenas)- Most common crab found on our seashores, they can grow up to 6cm (carapace width) but are usually smaller juveniles that are found in rockpools and under rocks on the lower shore. Their colouration can vary from a green/brown to a bright orange underside with many patterns and blotches. Females will be moulting during the summer months with breeding following straight after. The female will can lay up to 185 000 eggs which she holds in an orange sac under a flap on the underside of her abdomen.

Beadlet Anemone. Copyright: Richard Shelmerdine

Common Limpet (Patella vulgate)- Found in large numbers at all levels of the tide line, they have a very strong muscular foot which it uses to stay attached to the rock which allows them to live in areas with strong wave action. They graze on algae and micro-organisms that grow and live on the rock surface. They return each day to what is known as a ‘home scar’ which they create using their shell to cut into the rock.

Copyright: Richard Shelmerdine
Green Shore Crab. Copyright: NAFC Marine Centre UHI

Beadlet Anemone (Actinia equina)- Very common anemone seen in most rockpools and on the underside of rocks below the high-water mark. When out of the water they retract their tentacles, extending them again once submerged in water. These tentacles are used to catch floating food which it then moves to the mouth parts in the centre of its body. They use their tentacles for defence giving any intruder or neighbouring anemone a sting.

Copyright: Richard Shelmerdine

Common Periwinkle (Littorina littorea)- Known locally as whelks these little snails are a common seashore inhabitant in Shetland. Preferring rocky areas with good weed cover where they feed on different types of algae. This species is of commercial importance, they are gathered by locals and sold to the vivier trucks (trucks with seawater tanks used to transport live seafood) which visit the isles before travelling south as far as France and Spain to be sold on.

Dog Whelk. Copyright: Richard Shelmerdine

Dog Whelk (Nucella lapillus)- Found on most rocky shores in Shetland the Dog Whelk is similar to the Common Periwinkle but generally paler in colour with spiral ridges. Unlike the Common Periwinkle who are strictly vegetarian, Dog Whelks are carnivores, preying on barnacles, mussels and other bivalves. They use their mouth parts, known as a proboscis, to force open the shells of bivalves (mussels and clams) or drill a hole in the shell of its prey to remove the flesh inside. They are also NOT edible as they are apparently ‘distasteful’.

Butterfish (Pholis gunnellus)- A small eel-like fish up to 25cm long with continuous dorsal fin running the length of its body. They are a red/brown colour distinguishable by the ~12 black spots outlined with white along the base of the dorsal fin. They can be found in rock pools or in very shallow water underneath stones. Their skin is covered in a slimy coating making they very difficult to catch by hand, hence the name. They are the most commonly seen fish in rock pools in Shetland.

Common Starfish. Copyright: W.carter / CC0

Common Mussels (Mytilus edulis)- A very important commercial species in Shetland with 80% of Scotland’s mussels grown in Shetland. They are grown commercially on ropes suspended from header ropes held up on the surface by large floats. They are also common on our seashore where they can be seen in often very large groups (known as beds) attached to rocks using thin but very strong threads called basal threads. They are blue/purple in colour with size and shape varying dependant on environmental conditions. Even though they are edible, it is not recommended to eat wild mussels, being filter feeders, those in shoreline areas can contain a lot of sand making them gritty to eat, they can also ingest large quantities of E-Coli which can be found in run-off from surrounding farmland and septic tank run-off. Additionally, they can accumulate a naturally occurring, but toxic algae which is common in the summer and autumn.

Edible Sea Urchin. Copyright: NAFC Marine Centre UHI

Barnacle (Semibalanus balanoides)- Super abundant in Shetland found at all levels of the intertidal zone. Barnacles live an upside-down life; they are permanently cemented to the rock by their head and, when covered by water, feed with their feet (cirri). They famously have the largest genitals (about 15 cm) to body size ratio in the animal kingdom.

Sandhoppers. S. Rae from Scotland, UK / CC BY (https://creativecommons.org/licenses/by/2.0)
Butterfish. Copyright: NAFC Marine Centre UHI

Common Starfish (Asterias rubens)- Very abundant species in Shetland but scarce in rockpools except for occasional juveniles in low tide areas. Adults can however commonly be seen on pier and harbour structures. At their maximum they can grow up to 50cm but are more commonly seen to be around 10-30cm. They are orange/pale brown with 5 arms each with many rows of short tube feet which they use to move along the seabed. They can live on a wide range of substrate from sand, gravel to rocks and can sometimes occur in very large groups. They feed on a large range of species including bivalves, small crustaceans and other echinoderms. They use their tube feet to price open the shells of other creatures before extracting their stomach and placing it directly into the fleshy area to digest its meal. They have another clever adaptation where, if captured by predators, they are able to lose a leg to escape and will grow a new one, so if you spot a starfish with a leg smaller than the others, it is in the process of re-growing.

Common Mussels. Copyright: Rachel Shucksmith

Edible Sea Urchin (Echinus esculentus)- Known locally as ‘Skaadman’s head’.A large urchin around 15-16cm in diameter, they are red in colour, although shade may vary. They are covered in pinkish white spines and when submerged soft tentacles are extended in rows alongside the spines. They have a hard bony ‘beak’ on their underside which they use to feed on algae and barnacles.  They are scarce in rockpools but are often seen on piers and harbour walls. They are often found washed up on beaches, usually broken and with no spines left intact. They are known as the Edible Sea Urchin as the roe was eaten as a delicacy in some areas of the UK.

Barnacles: Copyright Richard Shelmerdine

Sandhoppers- Commonly found on sandy beaches under rocks or seaweed above the high-water mark. They can also be found along the strandline amongst rotting weed. They are a staple food source for many seashore birds include Turnstone, Oystercatcher and Ringed Plover. They get their name from the leaping movement they use to propel themselves away from danger.