Starfish

Overview

Asterias rubens is one of the most familiar and widespread starfish species in European waters. Typically displaying five robust arms radiating from a central disc, this echinoderm exhibits remarkable regenerative abilities and can regrow lost limbs. The species is characterized by its rough, spiny texture and variable coloration ranging from orange and red to purple and brown. This starfish inhabits rocky shores, mussel beds, oyster reefs, and various hard substrates from the intertidal zone down to depths of approximately 200 meters. It is a voracious predator of bivalve mollusks, particularly mussels and oysters, using its powerful tube feet to pry open shells and everting its stomach to digest prey externally. This feeding behavior has significant ecological and economic impacts on shellfish populations. Asterias rubens demonstrates remarkable physiological adaptations to marine life, including a water vascular system for locomotion and feeding, and the ability to tolerate varying salinities and temperatures. The species has been studied extensively in developmental biology and marine ecology, serving as a model organism for understanding echinoderm physiology and predator-prey dynamics in coastal ecosystems.

How to identify

Asterias rubens typically has five thick, tapering arms, though specimens with four or six arms occur. The upper surface is covered with short, blunt spines arranged irregularly, giving a rough texture. Coloration varies widely from orange-red to purple, brown, or violet, with paler tube feet visible on the underside. Adults typically measure 10-30 cm in diameter, though larger specimens exceeding 50 cm have been recorded. The madreporite (a small, pale circular plate) is visible on the upper surface near the center. The underside shows five ambulacral grooves lined with numerous tube feet.

Habitat

Rocky shores, gravel beds, mussel and oyster beds, kelp forests, piers, and breakwaters from the intertidal zone to depths of 200 meters. Prefers areas with hard substrates and abundant prey populations, particularly bivalve mollusks.

Distribution

Northeastern Atlantic Ocean including coasts of Norway, Iceland, British Isles, North Sea, Baltic Sea, and south to France and northwestern Spain. Also found along the Atlantic coast of North America where it was likely introduced.

Diet

Carnivorous predator feeding primarily on bivalve mollusks (mussels, oysters, clams, scallops), barnacles, polychaete worms, gastropods, and occasionally carrion. Uses tube feet to pull apart bivalve shells and everts stomach through mouth to digest prey externally.

Behavior

Slow-moving predator that uses tube feet powered by water vascular system for locomotion across substrates. Exhibits chemosensory ability to locate prey. Can right itself when overturned. Shows remarkable regenerative capacity, able to regrow lost arms and even regenerate entire individuals from a single arm attached to part of central disc. May aggregate in areas of abundant food. Tolerates variable salinity and can survive brief exposure during low tides.

Reproduction & life cycle

Dioecious with separate sexes releasing gametes into water column for external fertilization, typically in spring and early summer. Females can produce millions of eggs. Free-swimming bipinnaria larvae develop in plankton for several weeks before settling and metamorphosing into juvenile starfish. Can also reproduce asexually through autotomy and regeneration. Sexual maturity reached at 2-3 years. Breeding triggered by temperature and photoperiod changes.

When to look

Most active during warmer months (spring through autumn). Spawning occurs in spring and early summer (April-June in most regions). Can be observed year-round in suitable habitats, though may move to deeper water in winter.

Cultural significance

Widely recognized symbol of marine life and coastal ecosystems. Used in educational settings and marine biology research. Considered a pest species by commercial shellfish farmers due to predation on cultivated mussels and oysters. Historically collected for curiosity and decoration. Used in scientific research on regeneration, development, and marine ecology.

Similar species

• Asterias forbesi (Forbes' sea star)
• Marthasterias glacialis (spiny starfish)
• Crossaster papposus (common sun star)

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