Population dynamics of coastal forests of Macrocystis pyrifera in Puerto Toro, Isla Navarino, Southern Chile

Abstract

No clear idea exists on the roles of disturbance, competition and grazing as structuring agents of forests of Macrocystjspy7ifera plants in southern South America. Yet, these beds can be used to test specific ecological predictions gathered In geographically separated but physiognomically similar communities in the northern hemisphere. This study evaluates the validity of some of these predictions as they relate to the role of ecological factors regulating distributional patterns of a coastal population (40 to 50 m wide) of M. pyrifera in Puerto Toro, Navarino Island, southern Chile. Molphometric studies indicate statistically significant correlations between different parts of the plants so that plant length can be predicted from almost any holdfast dimension. Densities of juveniles of M. pyrifera across the belt are inversely correlated wlth densities of adult plants. Inter-plant distances increase significantly with plant sizes suggesting a density-dependent regulation of plant distribution within the belt. Removal of the floating canopy indeed allows for recruitment of juveniles inside the forest and results in significant changes of inter-plant distances. Experimental removal of Lessonia vadosa at the shallower end of the belt allows M. pyrifera to extend further into shallower water. Transplanting experiments indicate the deeper end of the belt to be set primarily by substratum availability. The M pyrjfera populations in Puerto Toro thus show a similar growth and reproduction strategy as those described for the North Pacific Ocean. The obviously different climatic and biological conditions have notorious effects only on plant sizes and production rates. INTRODUCTION