Publication Date

Summer 2025

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Environmental Studies

Advisor

Lynne Trulio; Rachel O’Malley: Joshua Smith

Abstract

Due to a myriad of factors, giant kelp (Macrocystis pyrifera) abundance along the California coast has decreased in select areas, leading to the formation of lower-diversity ecosystems dominated by purple sea urchins (Strongylocentrotus purpuratus), known as “urchin barrens.” While sea otters (Enhydra lutris) are keystone predators that help maintain kelp forests through predation on sea urchins, in Monterey, they avoid barren sea urchins due to their low energetic value and abundance of other habitat types, limiting their influence in these areas. From 2021-2023, sea urchin culling at Tankers Reef, a former barren site in Monterey Bay, was conducted to promote kelp recovery. This study combined long-term kelp canopy data (2010-2024), historical sea otter foraging records (2017-2024), and direct behavioral observations (June – October 2024) at five rocky reef sites to evaluate the role of sea otters in three alternative subtidal reef states. Results indicated that sea otters exhibit behaviors and prey selection patterns at Tankers Reef, similar to those in established kelp forests. Foraging in urchin barrens appeared to depend heavily on local habitat features and prey availability. While some urchin barrens offer access to viable prey, they may still pose long-term risks to sea otters due to higher energetic costs and increased exposure to toxins from elevated mussel consumption. This study contributes to growing literature advocating for the use of ecological theory in ecosystem restoration approaches, and findings suggest that sea otter foraging at Tankers Reef may reinforce kelp recovery.

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