Response of Ecklonia radiata (Laminariales) to light at 15 degree C with reference to the field light budget at Goat Island Bay, New Zealand

Gametophytes of E. radiata (C.Ag.)J.Ag. grew in culture at 15 degree C under daily quantum doses ranging from 0.86 to 360 cE m super(-2). Growth rates increased with quantum doses up to 40 cE m super(-2) d super(-1), then reproduction began and the relative growth constant declined while ovum release came earlier with increasing light up to about 100 cE m super(-2) d super(-1). Above 100 cE m super(-2) d super(-1) there were no consistent trends with increasing light, except that at the higher quantum doses, fertile female plants had fewer and larger cells and therefore fewer potential ova. Reproduction varied with daily quantum dose rather than with day-length. Plants grew fastest in low photon flux density, long daylength conditions.