Sea Otters: Keystone of the Kelp

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Fun fact. Though I retired from academia in 2023, after 3 years of tragic life events, my career as a scientist never slowed down. My passion for science and conservation did not wane and as I continued to heal, my productivity also soared - I continue to actively publish scientific papers, run workshops, advise students, and serve as a guest associate editor.

My best science has always been inspired by immersion in nature. Last weekend, while salmon fishing in the San Juan Islands, Jenn and I came across a sea otter floating on its back, munching on a sea urchin. Sea otters are a keystone species for the Salish Sea kelp ecosystem, because they control the numbers of sea urchins. When urchin populations are left unchecked, they ravage kelp forests and destroy habitat for the hundreds of marine species that depend on healthy kelp. I chuckled when I looked across the water at the University of Washington Friday Harbor Research Labs, recalling that the term ‘keystone species’ was coined over 55 years ago by Dr. Robert Paine, a UW ecologist.

This encounter with a keystone species of the Salish Sea sparked memories from my early days as a biologist at Olympic National Park, where I grappled with how the keystone species concept could help guide practical on-the-ground conservation. With these ideas in mind as I began a PhD at University of California, Santa Cruz, I was thrilled to meet Dr. Jim Estes who a decade earlier had discovered the keystone role that sea otters played in kelp forest ecosystems, Over the next few years Jim and I, along with my dissertion advisor Michael Soule and Dan Doak, brainstormed and debated the question: How can this idea that all species are not created equal in their effects on ecosystem structure and function be used to advance both our understanding of nature and efforts to sustain it?

These musings evolved into two seminal papers that defined keystone species and its application to conservation. The first publication (in 1993) called for increased rigor in the use and application of the term. The paper created a big splash, and the United Nations Environmental Program (UNEP) noticed it as they developed standards for global biodiversity decision-making. They invited me to join a small but esteemed gathering of ecologists (including Paine, Estes, and Jane Lubchenco) in Hawaii, with a condition: we would be treated to the wonders of Hawaii only after came up with a consensus definition of keystone species. We rose to the occasion (even professors are motivated by free beer and fun at the beach), and emerged from the stuffy windowless conference room two days later with a precise definition: A keystone species is one whose impact on its community or ecosystem is large, and disproportionately large relative to its abundance. We published the details of this definition in 1996. Together, the 1993 and 1996 keystone species papers have been cited 5000+ times.

       Watching that otter munching on an urchin, thereby helping to sustain dozens of species in the kelp forest ecosystem, was just one of many moments of the past couple of years that have energized me to continue teaching students and helping with research that applies population ecology science. More to come!