Document Type


Date of Degree Completion

Spring 2019

Degree Name

Master of Science (MS)



Committee Chair

Lixing Sun

Second Committee Member

Paul W. James

Third Committee Member

Clay Arango


Pisaster ochraceus is a common west coast sea star whose predation of Mytilus californianus (the California mussel) increases the biodiversity of its intertidal community. Sea star wasting disease is an illness that causes sea star tissues to become necrotic until the creature wastes away and dies. In 2013, a coast wide outbreak of sea star wasting disease caused a mass mortality event in P. ochraceus. The goals of this study were to try to identify some of the possible causes for the outbreak, as well as analyze the impact that sea star wasting disease prevalence has on biodiversity. In this study, forty tide pools in four different regions of Washington State (northern coast, southern coast, northern Puget Sound, and southern Puget Sound) were surveyed for Shannon biodiversity, species richness, abundance of P. ochraceus, percentage of P. ochraceus infected with sea star wasting disease, total dissolved solids, pH, alkalinity, and salinity. Four separate statistical models were performed testing percentage of P. ochraceus with sea star wasting disease, presence of sea star wasting disease, Shannon biodiversity, and species richness as the response variable. Nothing was statistically significant for presence of sea star wasting disease, percentage of P. ochraceus with sea star wasting disease, and species richness. However, Shannon biodiversity had a positive correlation with abundance of P. ochraceus and a negative correlation with percentage of P. ochraceus with sea star wasting disease. This negative correlation suggests that the mere presence of sea star wasting disease is enough to negatively influence P. ochraceus populations by disabling their ability to eat, which drives down biodiversity. The data suggests that even before a sea star dies; it is not functioning as a predator. However, neither location nor water quality appeared to influence biodiversity or sea star wasting disease, which suggests that further research should be conducted on these variables and others to try to identify a causal agent for these outbreaks.



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Biodiversity Commons