When were sea otters first recognized as a keystone species?

Sea otters became famous in ecology after work in the 1960s showed how their presence strongly affected kelp forest communities. By eating sea urchins, otters helped prevent urchins from overgrazing kelp, which supports many other species. The broader ecological idea was formalized by Robert Paine, who introduced the term “keystone species” in 1969. Sea otters became a classic example of how a relatively small population can have an outsized impact on an ecosystem. The concept transformed conservation biology and ecosystem management.