Role of sea urchins on California kelp

The new research provides valuable information to understand and protect California's quintessential kelp forests

Date:  March 14, 2019

Source:  San Diego State University

California sheephead and spiny lobsters may be helping control sea urchin populations in Southern California kelp forests, where sea otters -- a top urchin predator -- have long been missing, according to a new San Diego State University (SDSU) study published in the journal Ecology. The research provides new insight into the complex predator-prey relationships in kelp forests that can be seen in the absence of sea otters.

The study is also the first to experimentally test the relative impact, or rate of feeding, of the California sheephead and spiny lobsters in comparison to sea otters, whose historical range spanned from British Columbia, Canada to Baja California, Mexico.

"Healthy kelp forests are important both economically and ecologically along our coast. They act as nurseries and vital habitat for valuable fishery species, recreation sites for kayakers, free divers, and scuba divers, and serve as the base of rocky reef food webs," says Robert Dunn, who led the study as a Ph.D. candidate at SDSU and University of California, Davis, funded by a NMFS-California Sea Grant Fellowship.

Kelp forests rely on the proper balance of herbivory and predation. Sea urchins dwell on the seafloor where they forage on macroalgae, including giant kelp. If their populations are left unchecked by predation, they can decimate kelp forests and prevent kelp from growing. That can transform a thriving community of kelp into an oceanic desert, known as an urchin barren.

The relationships between predators and prey vary among communities. Sea urchins have recently decimated kelp forests in Northern California, leaving researchers to wonder why Southern California kelp forests have remained relatively intact without sea otters to control the urchin populations.

Past research has indicated that Marine Protected Areas in Southern California house a diversity of predators -- warranting fewer urchins and abundant kelp. Dunn and his SDSU graduate advisor, Kevin Hovel, set out to better understand the potential for top-down control by these two distinct predators: the California sheephead and spiny lobsters.

Continued