AbstractAnnual cycles of gamete development inMytilus edulisL. in south‐west Iceland were investigated during 1986 to 1987. Histological preparations of the gonads showed that all individuals were fully mature in the beginning of June in both years and one spawning period was recorded each year at a sea temperature of 10‐12oC. The main spawning took place from the middle of July to the middle of August, and from the middle of June to the end of July in 1986 and 1987, respectively. Redevelopment of the gonads after spawning was observed in February when both food availability, measured as chlorophyllaconcentration, and temperature were low. Rapid gonad maturation took place during the spring phytoplankton bloom in March‐April.Larval settlement was heavy on the artificial collectors used. The length of the larval period was estimated as being 4‐5 weeks and peak settlement occurred in the middle of September. The size of the early plantigrades settling on the collectors during the study period indicated direct settlement of mussel larvae from the plankton onto the collectors.One year after settlement the spat averaged 24.6 mm ± 6.0 (SD) shell length and two years after settlement a market size of 50.8 mm ± 5.7 (SD) was reached. Growth was correlated with food availability, measured as chlorophyllaconcentration. The growth season lasted from March to October with the greatest shell growth in late summer. The results showed that the growth of M.eduliswas markedly increased by suspending the animals in a more favourable environment than that found on the natural mu