Growth phenology of <i>Pleurophycus gardneri</i> (Phaeophyceae, Laminariales), a deciduous kelp of the northeast Pacific

Abstract

Growth phenology of the monotypic northeast Pacific kelp Pleurophycus gardneri was assessed between 1982 and 1984. The study gives evidence that Pleurophycus is a deciduous perennial. Pleurophycus shows complete and synchronous defoliation during a short period of time in late fall and commences new blade growth after about 2 weeks of quiescence. Pleurophycus sheds the lamina along an abscission zone at the transition between stipe and blade. The abscission zone is macroscopically evident through a change in color and a slight indentation in senescent plants. After separation, outer cortical cells constitute a protective layer which increases in thickness as new blade outgrowth progresses. Temperature of 14 to 15 °C is assumed to be a triggering factor for the induction of blade senescence. Warm water intrusion, associated with E1 Ninõ, induced premature blade senescence and blade abscission in 1983. Growth of the new blade is completely inhibited in darkness. The induction of new outgrowth is not mediated through a photoperiodic effect and showed no day-length saturation.