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).