Macrocystis and its environment, knowns and unknowns

Abstract

Macrocystis commonly dominates substantial expanses of the nearshore along coasts where it occurs. We discuss several physiological and ecological factors affecting Macrocystis populations, particularly as they may influence competition with other seaweed species. Successful competition for light appears to explain much of the success by Macrocystis in dominating its environment. Although nutrient limitation may sometimes curtail Macrocystis productivity, a role in competitive success has not been documented. Water temperature controls the large scale geographic distribution of Macrocystis, but usually is rather minor on a local scale. Water motion apparently does not have important affects on competition except for influences from wave exposure. Salinity changes may control Macrocystis distributions where large freshwater inputs occur into semi-enclosed embayments. Sedimentation may affect microscopic stages in the kelp life history, with differential effects on various competitive species. Encrustations and preferential grazing may affect competitiveness. Unstudied but probably influential factors include disease, plant aging and some aspects of nutrition. Interactions between all these factors are complex, but are under investigation by modelling techniques with some interesting findings that help explain and comprehend the ecology of this useful plant. © 1986.