Paine's doctoral research thesis was on the ecology of living
brachipods. As a postdoctoral fellow, he worked on the history and energetics of
opisthobranchs (marine gastropods). Much of Paine's work at the University of Washington focused on the organization of marine communities. It was here that much of his research on
keystone species occurred. In a noteworthy 1966 paper, Paine described a rocky
intertidal ecosystem in
Makah Bay in
Washington state, where top predator species help maintain biodiversity. This led to his 1969 paper in which he proposed the keystone species concept. This concept states that an ecosystem may experience a dramatic shift if a keystone species is removed, even though that species was a small part of the ecosystem by measures of
biomass or
productivity. It has become a very popular concept in
conservation biology. Paine also coined the term "
trophic cascade" to describe the top-down effects that occur in ecosystems when an important species is introduced or removed. ==Retirement and death==