Spiny sunstar

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Onglets

Description

Distinguishing features

The spiny sunstar is a very large, stocky sea star with 8 to 16 short, cone-shaped arms (usually 12 to 14). Short spines are clearly visible on its surface.

The relatively large central disk is orange, red or brown, often with small white spots. The base of each arm is white.

When a spiny sea star is examined from underneath, it can be seen that each arm has two rows of small tube feet, called ambulacral feet.

The mouth is also located on the underside, in the centre of the central disk.

Reproduction

Among sunstars, as among many other sea stars, the sexes are separate, meaning that there are both male and female individuals.

Fertilization is external: the males and females release their spermatozoa and eggs into the water, where fertilization takes place. The resulting larvae move about in the water. The following year, the young sun stars, which now live on the sea floor, are from 2 to 4 cm in diameter.

Over the next few years, they grow about 2 cm a year. As they grow, sun stars move from shallow sites into increasingly deeper water, at depths of up to 1200 m.

Diet

Spiny sunstars are dominant predators and as such play a major role in structuring animal and plant communities on the sea floor.

They feed on urchins, oysters, mussels, anemones, tunicates and even other sea stars. This means that spiny sun stars can limit the abundance of some other species of sea stars.

The largest spiny sun stars are even able to eat some crabs. If deprived of food for long enough, sun stars may even become cannibals and eat other sun stars.

Spiny sunstars have chemical sensors (chemo-receptors) that allow them to detect their prey and other sun stars.

Predators

The larger spiny sunstars are, the fewer predators they have. They are attacked by crabs and seagulls, for instance, which use their bills to cut off the tips of the sun star’s arms and eat them! Fortunately, sun stars are able to regenerate the lost parts. If attacked too frequently by predators, however, sun stars may weaken and even die.

Habitat

Spiny sunstars live in rather cold (4°C) saltwater and frequent rocky bottoms. Because they tolerate strong sunlight, they are found from the zone immediately below the low-tide zone to depths of more than 3 km.

They live in the Atlantic Ocean, from the Arctic to New Jersey, in the USA, including the Gulf of St. Lawrence. They can also been seen in Europe, from the Arctic to the north coast of Brittany, in France.

Ecology, behaviour

Spiny sunstars are territorial: they do not like having other sun stars anywhere close by.

Like other sea stars, they use their ambulacral feet to open the shells of mussels or oysters. They use the suction pads on their feet to grasp the surface and then force the two halves of the shell apart. The stomach is then everted through the mouth and partly inserted into the oyster or mussel. The digestive juices are released and digest the flesh inside the shell.

A spiny sunstar can also swallow its prey. If eating a sea urchin, for instance, it takes it in its mouth, digests the flesh and then ejects the sea urchin’s skeleton (also called the test).

A spiny sunstar is a powerful animal: The muscles in its arms coupled with the suction pads on its ambulacral feet can exert 25 kg of pressure per square cm. It also uses its ambulacral feet to move around, at up to 5 m per hour.

French name

Soleil de mer épineux, Crachat d'amiral

Scientific name

Crossaster papposus

Phylum

Echinodermata

Class

Asteroidea

Order

Spinulosida

Family

Solasteridae

Size

Average diameter: 25-35 cm Maximum diameter: 40 cm

Status

Common in its habitat

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