ABSTRACTThe role of environmental factors in seasonal succession of six clones of marine diatoms was examined by testing effects of various combinations of temperature (5°, 10°, 15°, 20°C) and photoperiod (10, 12, 14, 16 h) on time to germination of resting stages and subsequent vegetative cell division rates. Resting stages were induced in batch cultures using a low nutrient medium and a cold, dark period. A three‐factor ANOVA showed that species, temperature, daylength, and their interactions signficantly(P =0.0001) injuenced germination time and division rate. Resting stages ofChaetoceros similisCleve andOdontella aurita (Lyngbye) Agardh were most successful in producing populations of cells on warm, long days (20°C/16 h). Chaetoceros didymusEhrenberg andC. cinctusGran were most successful under more moderate conditions (15°C/14 h). Resting stagesof Ditylum bright‐wellii (West) Grunow germinated and cells divided rapidly under all conditions. No consistent pattern was evident withThalassiosira rotulaMeunier. We compared results of the laboratory study with environmental conditions prevailing during the presence of these species in a British Columbia fjord. Favorable growth conditions determined forC. didymus, D. brightwellii,andT. rotulawere similar to conditions present when these species were commonly found in