Crabs and Relatives

Belonging to the phylum ‘arthropod’, subphylum ‘crustacean’ these animals include the familiar crabs, lobsters, shrimps, prawns and barnacles as well as the smaller copepods, isopods and krill. Most crustaceans have two pairs of antennae and only two body segments – the ‘cephalothorax’ (fused together from the head and thorax) and the abdomen. Paired legs and appendages vary greatly – some being sensory while others are adapted for walking or swimming. Some crustaceans are also armed with a large pair of claws.

Edible Crab - Cancer pagurus

Photo credit: Paul Kay

One of the commonest crabs found around Lundy, it has a distinctive pink-brown colour with a ‘pie-crust’ edge to the shell and black-tipped pincers. Brown crabs are the species which most of us associate when thinking of crab sandwiches. The edible crab fishery is one of the oldest known to the British Isles. As such, potting for crabs is allowed as a sustainable activity around part of the Marine Conservation Zone) but is prohibited in a No Take Zone (NTZ) which covers just over 3 km2 on the east of the MCZ. The NTZ keeps the fishing activity away from the delicate species of sponges, cup-corals, Ross corals and colonial soft corals. These species are easily damaged by the abrasion caused by the raising and lowering of crab and lobster pots. Like humans these crabs are omnivorous, feeding on both plants and animals. During daylight cracks and crevices provide safety from predators such as wrasse, cuttlefish and seals. Brown crabs are easier to see at night, when they leave their hideouts and forage about on the seabed. They are easy to spot at night-time because their eyes light up pink in torchlight!

Common Lobster - Homarus gammarus

Photo credit: Keith Hiscock

These magnificent animals have ten legs and a hard exoskeleton (outer skeleton, rather than our internal one) which groups them in with other decapods (ten-legged animals) such as crawfish, prawns and crabs. Lobsters are a striking deep blue in colour, with bright red ‘whip-like’ structures (antennules) sprouting from the head. These antennules are used by the lobster to ‘feel’ its way around the environment, especially at night. One of the claws is distinctively larger than the other, especially in the older adults. Common Lobsters like to have a deep, dark crevice in which they hide when not foraging for food. Unfortunately they are no longer as common as the name suggests, mostly due to over-fishing

Crawfish – Palinurus elephas

Photo credit: Keith Hiscock

They actually look like giant prawns and are easy to distinguish from common lobsters. Crawfish do not have large pincers, unlike lobsters which have formidable claws, and are a deep orange-brown in colour, not blue like common lobsters. The long ‘whip-like’ structures protruding from the head (antennules) are usually alternately banded with orange-brown and white stripes. These strange structures are used by the crawfish to ‘feel’ around its environment. Crawfish like a nice hole to hide in. Unfortunately they are very scarce around most of the British coast, even at Lundy, due to historic fishing activities.

Spider Crab – Maja squinado

Photo credit: Paul Kay

This scary-looking animal is a large crab with long spider-like legs. The body of the shell can grow up to 20 cm long. Despite its appearance the spider crab is actually a herbivore, feeding only on plants. It can camouflage itself by sticking pieces of seaweeds and sponges onto its back and legs. This helps the spider crab hide from predators, such as wrasses and cuttlefish, especially when it is younger and smaller.

Barnacles

Photo credit: Keith Hiscock

There are numerous species of barnacle. The adults remain fixed in one place once anchored to a suitable rock surface. They occur in the intertidal area of exposed rocky shores in the high to mid shore area and are sometimes so densely packed that it completely covers the rock surface.

The juvenile stages of barnacles go through numerous changes - from planktonic free floating organisms - before settling into a suitable location by detecting the presence of other barnacles and suitable sites to grow into an adult.

They have armour-like wall plates all around and an opening at the top. Both these adaptations protect the animal from pounding wave action and also from prolonged exposure while the tide is out by trapping water inside. When the tide comes in the plates open and the barnacles wave their modified legs (called cirri) about in the water to filter out food. Barnacles are hermaphroditic, however they do not release eggs and sperm into the water, instead they use extendible penises to transfer sperm to receptive neighbours.