Reproductive cycles are described for subtidal and intertidal populations of the, starfish Asterias rubens L. and for a subtidal population of the starfish Marthasterias glacialis L. on the south-west coast of Britain. Intertidal A. rubens had a clearly defined reproductive cycle with spring-early summer spawning. Pyloric caecum indices were inversely related to gonad indices. Subtidal A. rubens had lower gonad indices and less seasonal variation in the pyloric caecum indices. Gonad indices of M. glacialis suggest few animals in the population studied were breeding, but it is likely that this species also spawns in summer.

Plankton samples and larval rearing studies suggest a planktotrophic pelagic life of approximately 90 days for A. rubens. Field observations and laboratory experiments show larvae settle on a wide range of substrata. Recruitment to an intertidal population of A. rubens at Hollicombe Reef occurred in July 1980 and September 1981. Growth of juvenile starfish was followed for 17 months. Juvenile starfish feed carnivorously at the completion of metamorphosis. Early growth is rapid; however, there is a reduction in the growth rate during winter months. Feeding and growth of juvenile A. rubens is compared with published data on juvenile starfish of other species.

The gonadial, pyloric caecal and somatic cycles over three consecutive years in a subtidal population of the starfish Marthasterias glacialis from Plymouth Sound are described. The study area lies towards the eastern limit of the up-Channel range of this species, and this is reflected in only partial reciprocity between gonadial and pyloric indices, and also by the apparent utilisation of somatic material during the build-up of gametes. The sequence of events at the cytological level during gonadial build-up is described.

Gonadial, pyloric caecal and somatic indices and oocyte size-frequencies are compared over a 3-year period for the starfish Asterias rubens from an intertidal nutritionally rich site and a subtidal impoverished site from the English Channel off south-west Britain. The intertidal population showed significantly higher values for all three indices over most of the study period compared with the subtidal population, and its spawning occurred later. The somatic index of the subtidal population showed a steeper rise than the intertidal population over that part of the cycle in which the gonads were undergoing enlargement, which gives further support to the suggestion that starfishes deprived of sufficient food may give priority to maintenance of the body-wall over enlargement of either the food-storage tissues of the pyloric caeca or the gonads.