Details
Asterias rubens
A five-armed sea star of the northeast Atlantic, brick-red above with a single row of short white spines down each arm. It is famous for prising open mussels and everting its stomach to digest prey outside its body.
Map: Ecoregions 2017 © RESOLVE (CC BY 4.0) · Natural Earth (PD)
It ranges through the northeast Atlantic from Norway and Sweden across the North Sea around Britain, France and Iberia south to Senegal, and in the western Atlantic from Labrador to Florida. It favours rocky and gravelly seabeds and tolerates brackish water.
It usually has five arms that are broad at the base and taper to a point, most specimens spanning 10–30 cm though some exceed 50 cm. The upper surface is orange to brick-red with a central line of short white spines flanked by soft papulae, while paler purples and browns also occur.
It lives a solitary life with no fixed daily rhythm, creeping slowly over rock on countless tube feet on its underside. It can regenerate lost arms and takes evasive action when it detects the scent of a predator.
A generalist carnivore, it eats bivalves, gastropods, barnacles, polychaete worms, other echinoderms and carrion. It pries shells apart with its tube feet, pushes its everted stomach through a gap as narrow as a millimetre, and digests the prey externally, homing in by smell.
Sexes are separate and spawning occurs in spring, a moderate-sized female releasing an estimated 2.5 million eggs. Fertilisation happens in open water and the planktonic larvae drift for about 87 days before settling; there is no parental care. Lifespan is roughly seven to eight years.
An abundant and familiar shore animal, it secretes a saponin-like substance that repels predators and warns prey such as whelks. Mass strandings sometimes wash large numbers ashore for reasons that often remain unclear.
