Ecological Implications of Culture Studies on Nereocystis Luetkeana1

SUMMARY Meiospores, gametophytes grown in culture and then fragmented in a blendor, and young sporophytes of N. luetkeana, were grown at varying temperatures, light intensities, photoperiods, and densities. Vegetative growth occurred over a wider range of environmental conditions than did sexuality. Gametophytes matured at 5, 10, and 15 C but not at 20 C. Low light., 15 ft‐c (161 lux), and short day photo‐periods (8–16) inhibited or greatly retarded sexuality. Saturation intensities for sexuality occurred between 100 and 200 ft‐c (1076 and 2152 lux). Maximal rates of sexuality occurred at or above light, intensities of 3200 ft‐c hr/day on an alternating (16–8) light‐dark cycle. Light was determined to be the single most important factor in sexuality and subsequent sporophyte growth. Increased density did not affect sexuality but significantly reduced sporophyte growth. Field light intensities beneath lower canopy kelps were below minimal light requirements for gametophyte maturation. These data support, the view that light sets the lower limits on vertical distribution and that, temperature is involved in the latitudinal range of N. luetkeana. These and other studies suggest that the anomalous shallow water depth distribution of N. luetkeana in the San Juan Islands is partly the result of competition for light and not light attenuation, per se.