A landmark 45-year study led by Scripps Institution of Oceanography shows shrinking forests and points to the importance of long-term studies.

La Jolla and San Diego’s giant kelp forests are disappearing, according to a landmark new study led by scientists at UC San Diego’s Scripps Institution of Oceanography that underscores the value of long-term research and the need for concerted conservation efforts.

Giant kelp forests – two of which lie off the coasts of La Jolla and Point Loma –  are crucial elements of a healthy ecosystem, providing homes and producing food for several animal species.

Scripps marine ecologist Ed Parnell seeks to use scientific methods to create the most effective marine reserves/Image courtesy of Scripps Institution of Oceanography

A decimated kelp forest means starving animals, according to SIO marine ecologist Ed Parnell, first author of the recently-published study.

Kelp forests also feed other ecosystems nearby, Parnell said, fueling animals that live off shore including into submarine canyons and benthic (bottom-dwelling) creatures.

Onshore, kelp wrack, the piles of kelp on the sand, are a food source for worms and small crustacea that feed migrating birds. 

A lack of food means a lack of structure, Parnell said, all of which starts in the now-disappearing giant kelp forests.

The study spans a unique length of time – 45 years – following individual kelp plants and observing how “the dynamics of those kelp plants has changed over time,” Parnell said.

The findings reveal chronic stressors, like marine warming, limit the giant kelp’s regrowth abilities, as the kelp doesn’t have enough time to grow back.

Typically, after a disturbance like an El Niño (a year with warmer water) or a big storm, “there’d be a massive die off of giant kelp,” he said, followed by a slow regrowth.

But “the time between disturbances is decreasing,” Parnell said, “and the amplitude of the disturbances … are increasing.”

Disturbances are primarily ocean heat waves (including an intense spike in 2014-15 that led to a “big issue” with kelp death) but also include storm waves and other biological disturbances that change the dynamics of kelp growth, he said.

Water pollution historically has affected kelp growth in other parts off the California coast but is “not a big problem in San Diego,” Parnell said.

The study showed back in the 1980s and 1990s, the kelp were more resilient, much larger and more reproductive. 

A healthier kelp forest is an abundance of shelter and food (Sept 2024)/Image courtesy of Flo Li

Giant kelp can win “as long as conditions are right to grow,” Parnell said, adding he’s concerned that within a few more decades, “we’ll lose our kelp forests.”

The length of the study allowed researchers to “put things into perspective,” he said. “It’s a story of kelp forest loss.”

The study is outstanding not only for its length but also for the number of kelp plants studied – the scientists kept track of 14,000 plants to help them understand changes over time.

Moving forward, the study serves as a call to action for possible strategies to help, Parnell said, adding he’s a member of the California Ocean Protection Council, tasked with developing a kelp forest restoration plan to manage the kelp along the entire California coast (which contains both giant kelp and bull kelp, a Northern California variety). 

One answer may lie in the genetic makeup of the kelp forest further south that can withstand warmer water; scientists could develop a way to engineer plants that might grow better off La Jolla and San Diego even as the water warms.

Above all, Parnell said, the study offers a solid context for “predicting what’s going to happen with warming in the future.”