Longest-ever study finds San Diego's giant kelp forests in decline

Forty years of data from Scripps Institution of Oceanography show climate change is the main driver of the shrinking kelp forests.

Published on Mar. 8, 2026

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A new study from Scripps Institution of Oceanography has found that San Diego's iconic giant kelp forests are diminishing due to the effects of climate change. The study, which tracked 14,000 individual kelp plants over 40 years, shows a steady decline in kelp not attributable to natural cycles. Researchers say rising ocean temperatures, nutrient loss, and increased grazing by sea urchins are the main factors behind the kelp's decline, disrupting the local ecosystem.

Why it matters

Giant kelp is a keystone species in the San Diego coastal ecosystem, providing food and habitat for numerous marine species. Its decline could have far-reaching impacts, affecting recreational fishing, seabird populations, and even beach conditions. The study's findings highlight the broader effects of climate change on sensitive ocean environments.

The details

The study, published in the journal Ecological Applications, analyzed 40 years of data collected by Scripps researchers. They tracked 14,000 individual kelp plants at 20 stations off Point Loma, creating detailed family histories of the kelp. The researchers found that kelp plants are not living as long or reproducing as successfully, with a pronounced decline starting in 2015 when a pool of warm water settled in the Pacific. Factors like increased parasites, nutrient loss, and sea urchin grazing in warmer waters are driving the kelp's diminishment.

  • The study's data collection began in 1973.
  • Researchers set up 20 stations to track individual kelp plants in 1983.
  • The bulk of the data was collected after 1983.
  • The kelp decline became especially pronounced starting in 2015.

The players

Ed Parnell

The lead author of the study and a marine biologist at Scripps Oceanography.

Kristin Riser

A study co-author who has worked at Scripps since 1990.

Paul Dayton

A study co-author who collected some of the initial data for the study dating back to the 1970s and later created the research stations in 1983.

Mia Tegner

The late researcher who co-created the research stations in 1983 with Paul Dayton.

Scripps Institution of Oceanography

The research institution that conducted the 40-year study on San Diego's giant kelp forests.

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What they’re saying

“It's kind of mind boggling to think of how much data we collected. It's probably the longest time series like this in existence and it's unique in that we followed individual plants.”

— Kristin Riser, Study co-author (timesofsandiego.com)

“What we are seeing now is kelp plants that don't live as long and can't make it to the point where they can be highly reproductive.”

— Ed Parnell, Lead study author (timesofsandiego.com)

“Climate change is the principal driving factor, but understory competition is a major proximal cause.”

— Paul Dayton, Study co-author (timesofsandiego.com)

What’s next

Legislators have taken notice of the kelp forest decline, but efforts to create a federal grant to support conservation and management of American kelp forests have yet to pass in the House of Representatives. In the meantime, Scripps researchers will continue to operate their research stations and collect data on the kelp forests.

The takeaway

The decline of San Diego's iconic giant kelp forests, documented in this unprecedented 40-year study, serves as a stark warning about the far-reaching impacts of climate change on sensitive ocean ecosystems. The findings underscore the need for urgent action to address the root causes of global warming and protect these vital marine habitats.