A factorial experiment investigated the effects of irradiance and nutrients on the growth and death of germlings of Fucus serratus (L.) cultured at different densities. Nutrient status, which consisted of nutrient enriched or normal filtered sea-water, was found to be the most important factor. Under high nutrient levels in culture plant growth was greatly stimulated, resulting in a more variable/unequal distribution of plant sizes in the population which tended to be positively skewed. Nutrients and density interacted to shape the mean plant size of these seaweeds; under low nutrients there was no difference between densities, but at high nutrient levels plants in low density populations were larger than in high density ones. However, survivorship was not only dependent on nutrients but also on density and light levels. Fewer plants survived in high density populations in high nutrient conditions, but high density populations grown under low nutrient conditions seemed to be more susceptible to the harmful effects of strong irradiance.