• Asterias rubens is considered to be conspecific with Asterias vulgaris from the eastern seaboard of the United States of America and Canada (Coe, 1912).
• The size of Asterias rubens varies markedly with food availability and hence size is not necessarily a good indicator of age.

1. Vevers (1949) observed that with an abundant food supply, juvenile specimens of Asterias rubens could increase their radius at a monthly rate of slightly more than 10 mm in summer and autumn, and slightly less than 5 mm per month in winter.
2. Orton & Frazer (1930) recorded an increase in diameter of 2.5 mm per month on average, and 5.0 mm per month maximum in Asterias rubens.
3. Nichols & Barker (1984 b) followed the growth of annual cohorts in a population of Asterias rubens on an intertidal reef in Torbay, South Devon, UK, for three years. Growth was most rapid in the year following settlement and during the warmer months of the year. The average increase in starfish diameter over the first year was 28.5 mm, and over the second, 13.0 mm. The mean monthly increase in diameter over the three year period of the study was 2.2 mm. Starfish on the reef became sexually mature in their second year after attaining a diameter of 5 cm.

Feeding
Asterias rubens preys upon a wide range of living organisms and carrion that include molluscs, polychaete worms and other echinoderms. Occasionally, small crustaceans are caught on the suction discs of the tube feet. Asterias rubens preys upon bivalve molluscs by forcing the bivalve's shell open with its tube-feet, the tips of which attach to the bivalve shell by suction. Once a tiny gap (<0.1 mm) is established between the valves of the prey species shell, the starfish everts its stomach lobes into the bivalve and commences digestion.

Detailed experimental studies (Castilla & Crisp, 1970, 1973; Castilla,1972) have established that Asterias rubens has a well developed olfactory sense with adaptive preferences and avoidances. Asterias rubens demonstrates positive rheotaxis (purposeful movement of a motile organism in to a water current), which is enhanced in the presence of living prey such as Mytilus edulis (Castilla, 1972 ) and reversed in the presence of a predator Crossaster papposus (Castilla, 1972b).

Other species of the benthic fauna, including prey species Marthasterias glacialis, Buccinum undatumand several species of ophiuroids, demonstrate avoidance reactions in the presence of the predatory starfish Asterias rubens (Feder & Arvidssen 1967; Russell, 1984). These species can detect Asterias rubens owing to the release of a surface-active saponin from its body surface (Mackie et al. 1968).

Factors causing the aggregations of Asterias rubens are unclear but suggestions have been made that calm weather, amenable temperature and feeding conditions act together to give rise occasionally to aggregations. The occurrence of the phenomenon is dependent upon a large population of Asterias rubens larvae prior to the aggregation, which itself would be a function of good larval recruitment and growth conditions. Thus the irregularity of aggregations of Asterias rubens may be due to the need of a complex set of environmental variables to occur in the correct sequence over a number of seasons before an aggregation can occur. In addition, concurrent good mussel recruitment may also be required because an abundant prey source is a necessary focal point for the starfish (Sloan, 1980).

Reproduction
Asterias rubens is dioecious. The female produces small eggs that are released into the sea and fertilized externally to develop as planktotrophic larvae. It has been estimated that a female starfish of 140 mm diameter can spawn 2.5 million eggs (Fish & Fish, 1996).
Nutrient reserves in the pyloric caeca are an important source of energy for the process of gametogenesis and therefore food supply in the summer preceding spawning (when nutrients are deposited in the pyloric caeca) is an important factor determining fecundity (Jangoux & van Impe, 1977; Oudejans et al., 1979) (see adult distribution, additional information).
Larval settling time
Asterias rubens undergoes a complicated and protracted metamorphosis in the pelagic zone (see larval general biology). Advanced brachiolaria larvae reach a form when they are ready to settle around 87 days after fertilization, but some specimens have been observed, under laboratory conditions, to remain in the plankton for > 100 days without losing the ability to settle eventually and complete metamorphosis (see larval general biology & distribution) (Barker & Nichols, 1983).
Gonad parasitisation
In free spawning echinoderms the factors affecting larval production and survival ultimately control their reproductive success. Male Asterias rubens and Asterias vulgaris are liable to gonad parasitisation by the ciliate parasite Orchitophrya stellarum (Vevers, 1951; Bouland & Claereboudt, 1994). Orchitophrya stellarum causes complete atrophy of the testes leading to castration. The occurrence of the parasite is strictly seasonal and is only found between January and May when the hosts' testes are ripening or ripe. All that remains after the parasitic infection are the thick shrunken sheaths of the original testis tubules (Vevers, 1951). Infected males also show very weak carotenoid pigmentation and a general flabbiness of the body lacking the fresh turgid appearance of a healthy specimen (Nichols & Barker, 1984).
In a parasitized population of Asterias vulgaris from Canada, Bouland & Claereboudt (1994) observed a lower abundance of males, which were small in size and had a reduced gonadal index (gonadal mass/body wall mass) in comparison with the females. These observations implied an overall drop in spermatozoa production at the population level, thus parasitism of the male testes has implications for recruitment. In a turbulent flow as found in most benthic habitats, the success of fertilization is limited by the concentration of gametes. With fewer spawning males in the population, the fertilization rate will drop rapidly leading to a virtual sterilisation. The contribution of a parasitised population to the species reproductive effort would be negligible since the same number of planktonic predators and other adverse factors would be acting upon a reduced number of gametes.
A population of Asterias rubens on the Outer Grounds of the Eddystone, English Channel, was found to have >20% of males parasitised with Orchitophrya stellarum in March 1947. Although the evidence was speculative, a reduction in the population of Asterias rubens in the locality was subsequently observed in 1948, 1949 and 1950 as compared to 1947 (Vevers, 1951).