Environmental controls on spatial patterns in the long-term persistence of giant kelp in central California

As marine management measures increasingly protect static areas of the oceans, it is important to make sure protected areas capture and protect persistent populations and habitats. Rocky reefs in many temperate areas worldwide serve as habitat for canopy forming macroalgae and, in turn, these structure forming species of kelps (order Laminariales) often serve as important habitat for a great diversity of species. Macrocystis pyrifera is the most common canopy forming kelp species found along the coast of California but the distribution and abundance of M. pyrifera varies in space and time. The purpose of this study was to determine the relative contribution of various environmental parameters in predicting the spatial and temporal persistence of M. pyrifera along the central coast of California. Nine environmental variables considered in this study included depth of the seafloor, structure of the rocky reef, proportion of rocky reef, size of kelp patch, biomass of kelp within a patch, distance from the edge of a kelp patch, sea surface temperature, wave orbital velocities, and population connectivity of individual kelp patches. Results from a generalized linear mixed effects model (GLMM) demonstrated that the persistence of M. pyrifera was significantly associated with seven of the nine variables considered and are listed in order of their relative importance: distance from the edge of a patch, depth, complexity of the rocky reef, patch biomass, proportion of rock, wave-orbital velocities and population connectivity. These seven environmental variables were then used to predict the persistence of kelp across the central coast and these predictions were compared to a reserved dataset of M. pyrifera persistence. The environmental variables were shown to accurately predict the persistence of M. pyrifera within the central coast of California (r = 0.71, P