Photo Credit: Katie Davis Koehn
A long-term study by marine scientists at UC Santa Barbara has found that winter storm disturbance plays a greater role in determining the productivity of giant kelp forests than the availability of nutrients and other growth resources. Using two decades of monthly observations from the National Science Foundation-supported Santa Barbara Coastal Long Term Ecological Research (SBC LTER) program, researchers found that the amount of kelp surviving winter storms is the strongest predictor of the ecosystem's net primary productivity (NPP), a key measure of ecosystem health and the energy available to support marine life.
The findings, published in the journal Ecology and supported by the National Science Foundation, highlight how physical disturbance can have a greater influence on ecosystem productivity than resource availability.
“We found that giant kelp productivity is controlled less by how fast kelp grows and more by how much kelp survives disturbance,” said graduate student researcher Billie Beckley, lead author of the study.
Unlike many terrestrial ecosystems, giant kelp forests are continually reshaped by waves and storms that remove biomass and redistribute fronds and spores throughout the nearshore environment. These disturbances influence both kelp survival and the forest's ability to recover.
Daniel Reed, senior researcher at UC Santa Barbara's Marine Science Institute and co-author of the study, said long-term monitoring has been essential for understanding these highly dynamic ecosystems. Since researchers first developed a conceptual model of kelp productivity in 2008, the forests have experienced marine heat waves, purple sea urchin outbreaks and shifting sands that periodically bury reef habitat.
According to Reed, giant kelp forests are among the world's most productive ecosystems, but documenting that productivity requires frequent sampling because kelp grows and turns over so rapidly. Monthly field measurements allow researchers to capture biomass lost to storms, wave action, warm-water events and sea urchin grazing—changes that can easily be obscured by the kelp's rapid growth.
The National Science Foundation-supported Santa Barbara Coastal Long Term Ecological Research (SBC LTER) site
Using the expanded 20-year dataset, the team examined the amount of kelp present at the beginning of each growing season, the successful establishment of new plants and the growth of existing kelp. Their analysis showed that surviving winter storms had the greatest influence on annual productivity, while successful recruitment of young kelp also contributed significantly to the forest's recovery.
The researchers found that this pattern differs from most terrestrial ecosystems, where year-to-year productivity is typically driven by factors such as temperature, water availability, nutrients and soil conditions. Even during years marked by unusually warm ocean temperatures and prolonged periods of low nutrients, mechanical disturbance remained the dominant influence on kelp productivity. They note, however, that increasingly frequent or severe marine heat waves could still reduce productivity in the future.
It’s not just that kelp forests are an important ecosystem on our coast; it goes beyond that. Most of the production that happens in the kelp forest doesn’t stay in the kelp forest — it gets exported both into deeper water and to the beach where it plays a formidable role in shaping nearshore food webs.
The study also found that disturbance can have indirect benefits. Although storms remove mature kelp and reduce productivity in the short term, they also create open space and allow more sunlight to reach the seafloor, improving conditions for new kelp to establish.
Because giant kelp is a foundation species, its health supports a wide range of marine life. Much of the material produced in kelp forests is transported into deeper waters and onto nearby beaches, where it supports coastal food webs.
“It’s not just that kelp forests are an important ecosystem on our coast; it goes beyond that,” Reed said. “Most of the production that happens in the kelp forest doesn’t stay in the kelp forest — it gets exported both into deeper water and to the beach where it plays a formidable role in shaping nearshore food webs.”
Research for this study was also conducted by Bob Miller, deputy director and principal investigator at UC Santa Barbara's Marine Science Institute; Andrew Rassweiler of Florida State University; Max Castorani of the University of Virginia; and Jarrett Byrnes of the University of Massachusetts Boston.
Adapted from original reporting by Sonia Fernandez, “Disturbance has a greater effect on giant kelp productivity than does resource availability,” The Current, UC Santa Barbara, 2026.
Photo Credit: Ronald McPeak