Geographic Patterns in Intertidal Communities and Taxon Richness in Glacier Bay, Alaska: The Complex Spatial Interaction of Time since Deglaciation and Environmental Variables

Geographical patterns in species or taxon richness may illuminate processes producing or influencing the patterns. Historical factors such as deglaciation may leave a strong imprint on the communities that have since developed. The rapid and well-documented deglaciation of Glacier Bay, Alaska, following the Little Ice Age created an environment where rocky intertidal communities of varying ages (up to about 200 years) have developed. We used a multivariate approach to investigate the relationship of rocky intertidal community composition and richness to environmental gradients and time since deglaciation. Data for 25 rocky sites randomly selected from the entire bay was generated from sampling conducted from 1997 -2001. Is taxon richness significantly correlated with time since deglaciation? Yes. However, as might be expected from the legacy of melting glaciers in a fjord ecosystem, a number of oceanographic parameters are also highly correlated with taxon richness and community development. Which are the most important drivers of community composition throughout the bay? We investigated this using oceanographic data collected at a set of stations in Glacier Bay from 1993-2011, as well as time since deglaciation. The three physical parameters that showed the highest correlation to measures of community dissimilarity were July salinity, July sigma-t, and time since deglaciation. Principal components analysis (PCA) and bio-env analyses indicated that the oceanographic/geographic PCA component 1 was the most highly correlated with two measures of community dissimilarity. Increasing taxon richness was most positively correlated with high July salinity and position near the mouth of the bay. Cluster analyses indicated the similarity of communities at different sites, and provided further visual insight into the importance of geographical position in community development.