Common starfish

Common starfish live along rocky and sandy shores.

Some live in pools on the beach. Others live deep under the sea. They like places with lots of mussels to eat.

Common starfish live in the north-east Atlantic Ocean, from Arctic Norway down the coasts of Europe and south to Senegal in West Africa. A few turn up in the Mediterranean Sea.

They live everywhere from the seashore, where the tide goes in and out, to about 650 meters deep. You can find them on rocks, gravel, sand and mud, and especially in beds of mussels and barnacles. They live on every coast of Britain and Ireland.

MarLIN describes the species as abundant throughout the north-east Atlantic, from Arctic Norway along Atlantic coasts to Senegal, and only occasionally in the Mediterranean; Animal Diversity Web extends the northern limit to the White Sea. It ranges from the intertidal zone to 650 meters on rock, coarse and shelly gravel, sand and mud, and is common in mussel and barnacle beds.

Densities vary enormously: MarLIN reports 2 to 31 starfish per square meter on fine sand and hundreds per square meter on algal carpets. MarLIN notes that Asterias vulgaris of the North American east coast has been considered the same species, but records from North America are not included here.

Starfish move very slowly on their tiny feet.

If a starfish loses an arm, it can grow a new one. If it gets flipped over, it turns itself back.

Common starfish move slowly, about 15 centimeters a minute, gliding on many tube feet working together. If one gets flipped over, it twists one arm under, grips the ground with its tube feet and rolls itself the right way up. In stormy water it holds on tight and flattens itself against the rock.

A starfish can lose an arm to escape a predator and grow a new one. Growing back an arm can take one to two years.

Each tube foot can only extend or retract, but when many work in unison the starfish moves at around 15 centimeters (6 inches) a minute, and MarLIN records individuals crawling 5 to 7 meters a day. Overturned animals right themselves by twisting one arm until its tube feet grip, then rolling the body over as other arms join in. In heavy surf they clamp down and flatten their bodies.

Arms can be shed to escape predators and regrown; Animal Diversity Web reports regeneration of up to four lost arms, and MarLIN gives one to two years to regrow an arm. In shallow water the species sometimes gathers in dense aggregations of up to 100 starfish per square meter.

There are lots of common starfish in the sea.

Scientists have not given them a danger rating. If you find one in a rock pool, look gently and leave it in the water.

The common starfish is not on any endangered list, and the IUCN Red List, which rates the risk to wild species, has no assessment for it. In many places it is very common.

Starfish can be hurt when fishing nets are dragged over the sea floor, but their ability to regrow arms helps them recover. They eat a lot of mussels, the same mussels people gather and sell as food, so starfish can cost the shellfish business money. Pollution with the metal cadmium can harm how their eggs develop.

No IUCN Red List category has been assigned to Asterias rubens: MarLIN lists no global red list category and Animal Diversity Web lists no special status. The species is widespread, fecund and has long-lived larvae that disperse more than 10 kilometers, so MarLIN rates its ability to recover from disturbance as high.

Bottom trawling damages arms, and the share of starfish with regenerating arms has been suggested as an indicator of fishing disturbance; at the same time, discarded and damaged animals give these scavengers extra food. MarLIN calls it a voracious consumer of the marketable mussel Mytilus edulis, which gives it considerable negative economic importance. Experiments found that cadmium pollution slows ovary growth and causes defects in offspring.