Sea stars are keystone species in rocky intertidal communities. The removal of sea stars can create major shifts in the community composition of rocky intertidal shores. Sea star wasting disease caused large-scale mortality of Pisaster ochraceus populations along the Pacific coast of the United States. Sea stars’ densities are now increasing, but communities may still represent the shift that occurred during the period of sea star absence. In 2017, I collected data within the intertidal zones of eleven small islands within the San Juan Islands, sampling and recording all intertidal invertebrates and vertebrates in a minimum of six 0.25 m2 quadrats per island. At each island I also quantified presence of Canada geese, Branta canadensis, using a scale of "low," "medium," and "high" impact. I compared 2017 data to data collected in 2010-13 before sea stars declined from wasting disease.
Results/Conclusions
There was no significant difference in total abundance of intertidal organisms on islands with or without P. ochraceus for all years. However, there was a significant difference in richness on all islands across all years, with 2017 having the highest richness. There was no difference in abundance among islands with low, medium, and high goose impact, regardless of P. ochraceus presence. However, there was a significant difference in richness of organisms on islands P. ochraceus presence regardless of level of goose impacts. While this study provided some evidence for classic patterns of the keystone predator P. ochraceus, the spatial and temporal variation suggests that other factors may also be important in determining intertidal community structure.