Some of the earliest research on keystone species was conducted by robert t. paine, who actually coined the term keystone species. for over 25 years paine and his students removed pisaster ochraceus, a sea star, from tidal pools on the coast of washington. throughout his research, paine discovered that removal of this predator resulted in a) another predator moving in to replace the sea stars. b) a change in trophic levels, with only producers and herbivores present. c) mussels becoming the dominant species and crowding out all competitors. d) a shift in the ecosystem and a new keystone species becoming established.