Common Crustaceans of the shore

Common crustaceans of the rocky shore:

When it comes to rock pooling crustaceans are one of the most popular groups of marine organism; Crabs, Prawns, Shrimps, Sand Hoppers and Sea slaters are all familiar sea side fauna.  Crustaceans are mostly scavengers and will feed across the shore when the tide is in. When the tide is out the best place to look for crabs are under seaweed and beneath boulders, prawns and shrimps are most common in rock pools, sea slaters are usually higher up on the shore darting between crevices, whilst sand hoppers can be found amongst the strandline.

Below are images of the common species of crustacean you may encounter whilst rock pooling on the rocky shores of the UK:

Sea slater (Ligia oceanica) occurs on the uppermost shore and splash zone in and amongst crevices.

Sand hoppers (Taltrid amphipods) occur amongst the strandline of sandy shores.

Amphipods occur across the shore, usually amongst decaying seaweed or under boulders. 

A male and female amphipod embrace. 

Common Prawn (Palaemon spp) occurs in rock pools.

Common Prawn (Palaemon spp) occurs in rock pools.

Hermit crabs (Paguroidea) occur in rock pools.

Hermit crabs (Paguroidea) occur in rock pools.

The Green Shore Crab (Carcinus maenas) occurs across the shore amongst seaweed and beneath boulders.

Green Shore Crab (Carcinus maenas)

Green Shore Crab (Carcinus maenas), showing a defensive display after the boulder under which it was hiding was moved.

Green Shore Crab (Carcinus maenas) amongst anemone tentacles.

Green Shore Crab (Carcinus maenas) burried whilst the tide is out.

Green Shore Crab (Carcinus maenas) burried whilst the tide is out.

Velvet Swimming Crab (Necora puber) occurs under boulders of the mid to lower shore.

Velvet Swimming Crab (Necora puber)

Risso’s Crab (Xantho pilipes) occurs underneath boulders of the lower shore

Montagu’s Crab (Xantho hydrophilus) occurs underneath boulders of the lower shore.

Broad- clawed Porcelain Crab (Porcellana platycheles) occur on the under-side of boulders in the lower shore.

Broad- clawed Porcelain Crab (Porcellana platycheles)

Squat Lobster (Galathea squamifera) occurs underneath boulders of the lower shore.

Dynamene bidentata - Males and female underneath a boulder of the lower shore.

Dynamene bidentata - Males and female underneath a boulder of the lower shore.

Edible Crab (Cancer pagurus) Small specimens may be found underneath boulders of the lower shore.

Edible Crab (Cancer pagurus)Larger specimens are found in the subtidal.

Edible Crab (Cancer pagurus)Larger specimens are found in the subtidal.

Brown Shrimp (Crangron spp) occur in sandy habitats, just where the surf breaks and can become trapped in pools as the tide falls.

Majiidae are a family of crabs some of whom occur in the lower shore amongst algae and beneath boulders.

Common Spider Crab (Maja brachydactyla) occurs subtidally but may be encountered on low spring tides or, washed up on the shore.

Common molluscs of the rocky shore

Guide to common Molluscs of the rocky shore:

Gastropods

Gastropods are one of the easiest marine organisms to find on the shore, namely down to the fact that they stay motionless, attached to the rock, whilst the tide is out. There are two main categories of gastropod, those that are herbivorous (asiphonate) and those that are carnivorous (siphonate).

The soft bodied part of the animal is contained within a calcareous shell which is produced as the animal grows.  Gastropods move by using their strong muscular foot and they navigate and feed with the sensory organs on their head. Those parts of the body that protrude from the shell when the animal is moving and feeding can be withdrawn into the shell when necessary and some species have a horny plate attached to the foot (uperculum) that acts as a seal when the foot is withdrawn.

Gastropods can be found all over the rocky shore with certain species characteristic of the upper, mid and lower shore. For examples the small and rough periwinkles occur in the upper-shore, whilst thick topshells tends to be in the mid shore where there are rock pools and further down in the lower shore are flat periwinkles and blue rayed limpets. Other species, such as limpets and dog whelks occur across the shore.

Gastropods will often be found in aggregations, in crevices, under over hangs, beneath boulders or, amongst seaweed. This is because they are trying to avoid drying out when the tide is out and exposure to strong wave action when the tide is in. Consequently it is important not to disturb or move gastropods as it could cause them unnecessary stress.

Below are images of common gastropods that can be encountered from the upper to lower shore whilst rock pooling in the UK:

Basic features of a gastropod.

Small periwinkle (Melarhaphe neritoides)

The small periwinkle can be found within crevices of the upper shore and splash zone, where it often co exists with the Rough periwinkle.

Periwinkles (Littorina sp)e can be found within crevices and beneath under hangs of the upper shore.

 (Littorina compressa)

Another type of  periwinkle that closely resembles the rough periwinkle.

Common Limpet (Patella vulgata)

The common limpet occurs across the seashore, where it grazes, returning to the same attachment point when the tide is out.

Common Limpet (Patella vulgata)
Often limpets may ‘tend’ an area of alga for their consumption; such areas are known as limpet gardens.

Common Limpet (Patella vulgata)

The shape of the limpet shell varies depending on age and location on the shore, with those higher up tending to be steeper than those lower down the shore.

A Limpet species
Due to their sessile nature limpets can become colonised by other organisms, in this case barnacles.



Dog whelk (Nucella lapillus)

The dog whelk occurs in the mid and lower shore down to a depth of approximately 30 m; it can be observed within crevices, under boulder overhangs, and amongst barnacles and mussels upon which it feeds.

Dog whelk (Nucella lapillus) can show variation in its morphology.

Edible Periwinkle (Littorina littorea) occurs across the shore.

Edible Periwinkle (Littorina littorea)

Edible Periwinkle (Littorina littorea)

Thick Topshell (Osilinus lineatus) occurs from the mid to lower shore, where there are rock pools.

Thick Topshell (Osilinus lineatus)

Thick Topshell (Osilinus lineatus)

There are two species of flat Periwinkle (Littorina obtusata/fabalis) that occur from the mid to lower shore amongst fucoid algae.

flat Periwinkle (Littorina obtusata/fabalis)

Grey Topshell (Gibbula cineraria) occurs lower down the shore, amongst fucoid holdfasts, within rock pools and within the under-boulder community.

Flat Topshell (Gibbula umbilicus) occurs lower down the shore, amongst fucoid holdfasts, within rock pools and within the under-boulder community.

Grey Topshell (Gibbula cineraria)

Flat Topshell (Gibbula umbilicus)

Painted Topshell (Calliostoma zizyphinum) occurs near the low water mark under overhangs and within the under- boulder community.

Painted Topshell (Calliostoma zizyphinum)

Netted Dogwhelk (Nassarius reticulatus) are scavengers that occur from the low water mark, where you may see them with their siphon protruding as they move amongst the sediment.

Netted Dogwhelk (Nassarius reticulatus)

Netted Dogwhelk (Nassarius reticulatus)

Three Spot Cowrie (Trivia monacha) occurs near the low water mark within the under- boulder community.

Three Spot Cowrie (Trivia monacha).

Blue Rayed Limpet (Patella pellucida) occur from the low water mark and show two forms depending on whether they live on the fronds of algae or, within Kelp holdfasts.

Blue Rayed Limpet (Patella pellucida)

Blue Rayed Limpet (Patella pellucida) and Oysters (Anomiidae) can be found within the under-boulder community and growing on kelp holdfasts.

Gibbula magus occurs below the low water mark but can occasional be encountered on spring tides.

 Bivalves:

Bivalves are molluscs whose soft body is contained within to calcareous valves. Most bivalves live within the sediment although some live attached to rock and alga holdfast and can be observed within the rocky shore.

Blue Mussel (Mytilus edulis) occurs on exposed to moderately exposed shores within crevices or forming beds across the available substrate.

Blue Mussel (Mytilus edulis)

Blue Mussel (Mytilus edulis)

Scallop (Pecten maximus)

Opisthobranchs:

Opisthobranchs or sea slugs have evolved so that the shell is internal or absent. These organisms are confined to the rock pools and within the under-boulder community.

Grey Sea Slug (Aeolidia papillosa) occurs amongst fucoid fronds and beneath boulders of the lower shore.

Sea Hare (Aplysia punctata) occurs within Ulva spp. dominated rock pools or, at during breeding in aggregations at the low water mark.

Yellow Plumed Sea Slug (Berthella plumula) occurs within the under- boulder community

Yellow Plumed Sea Slug (Berthella plumula)

Sea lemon (Archidoris pseudoargus)

Green Sea Slug (Elysia viridis) occurs within rock pools of the mid to lower shore.

Green Sea Slug (Elysia viridis)

Prosobranchs

Philinidae

Philinidae

Polyplacophora (Chitons) are molluscs that appear 'shield like' and can be found attached to shells and boulders on the lower shore and amongst the under-boulder community.

Polyplacophora

Acanthochitona sp.

Watch out for Hermit Crabs living in old gastropod shells!