Helping kelp

Sea otters, like this one caught snoozing in the Monterey Bay, today have fewer spots to park themselves due to recent, atypically massive declines in the kelp forests that usually blanket a good deal of Northern California coastal waters. The origins and extent of this ecological upset, as well as potential interventions to address it, are a focus of research for the Raimondi-Carr Lab. Credit: Pixabay (CC0).

With the die-off of the sea stars that kept them in check, populations of purple sea urchins have exploded, contributing to massive declines in kelp forests along the California coast and replacing them with “urchin barrens” like the one seen here. Credit: Katie Davis/UC Santa Barbara (public domain).

In 2014, kelp, an iconic feature of coastal California, started dying—and kept dying. Per a UC Santa Cruz-led study published in 2021, the once lush forests of this bulb-topped, giant algae off the California coast had, by 2019, receded by more than 95%. Taking their place? A barren sea floor crawling with spiny sea urchins.

Historical records indicate that kelp abundance cycles with environmental conditions, typically declining as coastal waters warm. But the latest die-off appears poised for persistence. An atypically dogged warm water mass lasting from 2014 to 2016 (nicknamed “The Blob”) likely initiated the kelp decline. But then, a strong El Niño followed. The unusually extended warming exacerbated disease-related die-offs of the sea stars that eat urchins. Not surprisingly, the numbers of purple sea urchins—the voracious primary predators of kelp—exploded. How long this possibly climate change-related ecological upset will last is unclear. “I think the kelp will return,” said Professor Peter Raimondi, who co-leads the coastal ecosystem-focused Raimondi-Carr Lab with Professor Mark Carr. “The more important question is will such die-offs become more common.”

In a step towards potentially helping kelp to recover, Raimondi’s genetics-based research has identified kelp subpopulations adapted to thrive at different water temperatures. If coastal policy called for human intervention, Raimondi said, “You could theoretically restore kelp populations from a “seed bank” with stock adapted to current or expected temperature ranges.”

—Bethany Augliere