UBC Theses and Dissertations

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UBC Theses and Dissertations

A marine megafaunal extinction and its consequences for kelp forests of the North Pacific Bullen, Cameron David


Restoration of lost ecosystem functions and species interactions is increasingly seen as central to addressing the extensive degradation of ecosystems and associated losses of biodiversity and ecosystem services. To be effective, such restoration efforts require an understanding of how ecosystems functioned prior to human-caused extinctions and ecological transformations. Global declines of megafauna, such as the extinction of the Steller’s sea cow, are largely a consequence of human action and likely had significant and widespread ecological impacts. Drawing on historical evidence, kelp forest ecology, and extant mammalian herbivore ecology, I first propose six discrete hypotheses about the effects Steller’s sea cows may have had on North Pacific kelp forest dynamics. The natural history observations, historic accounts, and ecological evidence I review offer partial support for these hypotheses. Accordingly, I argue that Steller’s sea cows exerted a significant top-down influence in kelp forests, likely affecting physical ecosystem structure, productivity, nutrient cycling, species interactions, and the export of nutrients to surrounding ecosystems. Next, I build upon these hypotheses to develop an ecosystem model which re-introduces this extinct megaherbivore and highlights its former role in ecosystem dynamics and species interactions in kelp forests. I find that, while not a keystone species, Steller’s sea cows likely had a significant effect on ecosystem dynamics, influencing community composition and increasing the productivity and resilience of kelp forests. The model indicates the presence of Steller’s sea cows may also have enabled the coexistence of sea otters and some large invertebrates, suggesting that the often-seen decline of invertebrate populations caused by sea otters may be a phenomenon exacerbated by lost ecosystem functions and species interactions associated with the extinction of the Steller’s sea cow. My findings suggest that kelp forest dynamics and resilience were significantly altered prior to the influence of more recent and well-known stressors, and demonstrate the important ecological roles that can be lost with megafaunal extinction. This work also illustrates the degree to which the loss of species interactions has likely affected North Pacific ecosystems, and how using ecosystem models to consider past ecosystem dynamics can inform management and restoration of current social-ecological systems.

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