Poking the Paradigm

New research on sea urchins challenges long-held assumptions about marine reserves

February 17, 2021
A Garabaldi and several señorita swim past red and purple sea urchins. Credit: Ron McPeek
A Garabaldi and several señorita swim past red and purple sea urchins. Credit: Ron McPeek

Deprive a mountain range of its wolves, and soon the burgeoning deer population will strip its slopes bare. “I now suspect that just as a deer herd lives in mortal fear of its wolves, so does a mountain live in mortal fear of its deer,” wrote ecologist Aldo Leopold in his landmark 1949 title “A Sand County Almanac.”

Leopold proposed that predators keep herbivore populations in check to the benefit of an ecosystem’s plant life. Remove one link in the food chain, and the effects cascade down its length. The idea of a trophic cascade has since become a mainstay in conservation ecology, with sea urchins as a prime example just off the California coast.

“Urchins play a key role in the kelp forest because they eat kelp,” said Katrina Malakhoff, a doctoral student in UC Santa Barbara’s Interdepartmental Graduate Program in Marine Science. “And there are times and places when urchins eat so much kelp that they actually end up removing it all and creating urchin barrens.”