9633329 REED Kelp forests, dominant features of subtidal temperate reefs worldwide, undergo relatively frequent and unpredictable local extinctions and recolonizations. This project is a continuation of ongoing investigations of the causal mechanisms that allow for rapid forest recovery following widespread kelp loss. The objective of the project is to predict the frequency of occurrence and relative importance of the physical and biological conditions that promote extended spore dispersal in giant kelp (Macrocystis pyrifera) and determine: (1) the role of spore immigration rates in regulating the dynamics of local kelp populations and (2) the potential for limited dispersal to destabilize populations by reducing individual fitness. The research approach is to collect measurements of water motion simultaneously with measurements of spore release and dispersal from isolated plants over a wide range of physical and biological conditions. This information will be used to build an individual-based model that will predict effective spore dispersal within and away from a local population for varying conditions of water motion, plant fecundity, plant spacing, spore release, and population size. Predictions from the model will be tested using an experimental population of adult plants. The model will also be used to predict the frequency and spatial extent of self-fertilization under different conditions of water motion, plant fecundity, plant spacing, spore release, and population size. The effects of self-fertilization on individual fitness will be experimentally determined for all life stages. The information obtained from the project will apply generally to dispersal patterns of a large number of sessile marine organisms that release competent spores or larvae into nearshore waters. The general significance of this work is that it will provide much needed insight into the hydrodynamic conditions that promote extended propagule dispersal and the degree to which propagule immigration influences t he dynamics of species perceived to have relatively closed populations. Additionally, the individual-based approach to this study will provide information on spore dispersal away from individual plants, which will be used to evaluate the costs of self-fertilization in giant kelp, a member of a dominant group of temperate marine algae whose life history and dispersal characteristics place them at high risk to the adverse effects of self-fertilization. ***
