“Perfect Storm” Decimates Northern California Kelp Forests

photo by A. Maguire
kelp cover maps
Comparison of kelp cover at four important abalone fishery sites in 2008 and 2014. Green indicates kelp canopy observed. Maps created from data collected during CDFW aerial surveys. (Data: M. Fredle)

Northern California kelp forests have been reduced to an all-time low due to a “perfect storm” of large-scale ecological impacts. The California Department of Fish and Wildlife (CDFW) marine invertebrate management team has conducted annual ecosystem surveys of kelp forests in Sonoma and Mendocino counties since the late 1990s, and recent observations have caused concern about the state of the kelp forests. The severe reduction in kelp has already impacted the recreational red abalone fishery and commercial red urchin fishery, two economically important fisheries in northern California.

Abalone and Urchins Starving

Bull kelp (Nereocystis luetkeana), usually common on the northern California coast, has declined dramatically since 2014. Kelp forests are now 93 percent smaller compared to previous years, creating starvation conditions for herbivores.

abalone and kelp
Unusual foraging behavior near Elk in Mendocino County: a large red abalone climbing a bare kelp stalk trying to reach fronds that are not there.
photo by K. Joe

Abalone and sea urchins are both herbivores that depend on healthy kelp forest ecosystems for food and habitat. With the recent loss of kelp and the ensuing starvation conditions, researchers have documented unusual behavior for both abalone and urchins. Large abalone are now more commonly observed climbing stalks in search of kelp blades, and small abalone have abandoned the protection of rocky crevices in search of food. Other invertebrates and fish species, such as rockfish, also depend on the shrinking kelp forest ecosystem for food and protection from predation.

The Perfect Storm

perfect storm graphic
The “perfect storm” of ecological impacts illustration by A. Amrhein

A series of large-scale catastrophic events recently combined into a “perfect storm” of ecological impacts that triggered dramatic shifts in the kelp forest ecosystem on the north coast. Environmental stressors included impacts from a toxic algae bloom off the Sonoma coast in 2011, a widespread sea star disease in 2013 that was followed by an explosion in the sea urchin population, and the warm water conditions that have persisted offshore since 2014.

Harmful Algal Bloom

HAB aftermath
Aftermath of the harmful algal bloom: dead abalone and other invertebrates washed up on shore at Fort Ross in 2011.
photo by N. Buck

The first major impact to the region occurred in August 2011 when a harmful algal bloom released a toxin into Sonoma County waters, killing large numbers of marine invertebrates. The California Fish and Game Commission responded to this unprecedented event by instituting a temporary emergency closure of the abalone fishery in Sonoma County, followed by reductions in the annual abalone catch limits starting in 2014. This event marked the beginning of a set of ecological stressors that would impact multiple invertebrate fisheries on California’s north coast.

Sea Star Wasting Disease

Two years later in 2013, Sea Star Wasting Disease killed large numbers of sea stars on the West Coast of North America, from Mexico to Alaska. Sea stars are important predators of invertebrates that live in the kelp forests. The loss of these predators added another stressor that would later contribute to a sea urchin population expansion.

urchins and abalone
Large aggregations of purple urchins are wiping out kelp forests, creating pink barrens and out-competing other species, such as abalone, for space and food.
photo by A. Maguire

Purple Sea Urchin Population Boom

CDFW researchers have discovered that purple sea urchin densities are now greater than 60 times their historic density in northern California. This unprecedented expansion of urchin populations spans hundreds of miles of coastline. Purple sea urchins are voracious consumers of kelp. In large numbers, these small but hardy herbivores can easily wipe out vast expanses of kelp and other algae, changing the landscape from a lush and diverse kelp forest ecosystem to what is known as an “urchin barren”.

More sunlight reaches the sea floor in urchin barrens, because the light is no longer filtered through thick fronds of kelp canopy and sub-canopy – similar to the way sunlight is filtered through a rain forest canopy on land. Fish and other species that normally hide in the shade of these fronds are no longer protected from the hungry eyes of larger predators.

Purple urchins grazing a desolate kelp forest, Fort Ross, 2015.
photo by A. Weltz

In urchin barrens, the sea floor is dominated by the purple and red spines of urchins as they scour the rocks for food. Only the hard, calcified, pink crustose algae can withstand the high-impact grazing pressure currently observed in northern California. The urchin barren conditions may persist until the presence of sufficient predators, disease, or storms reduce the exploding urchin population.

Unprecedented Warm Water

The kelp forest ecosystem suffered another series of shocks in 2014 and 2015, when coastal water temperatures along the West Coast rocketed upwards due to a combination of oceanographic features: the “Warm Blob” in 2014, combined with a strong El Niño that began in 2015. Kelp and many other marine species are very sensitive to changes in water temperature, and warm water holds few of the nutrients required for kelp growth.

water condition diagrams
Summer water temperatures. The impacted area on the California north coast is circled.

Challenges to Kelp Recovery

The recovery of canopy-forming bull kelp is a critical concern for many of the nearshore commercial fisheries in California. The lack of kelp and associated loss of species diversity may also reduce recreational fishery enjoyment in affected areas. Bull kelp, common on the north coast, is very sensitive to warm water, and can die in water temperatures above 63°F (17°C). Bull kelp recovery may be limited even if ocean temperatures cool because kelp spores are vulnerable to intense urchin grazing, which can prevent the re-establishment of kelp beds. Successful re-establishment of new kelp every year is critical, because bull kelp is an annual species that lives for only one year. Without successful reproduction every year, the kelp forest may be unable to grow back to its full potential.

bull kelp biology diagram
Bull kelp spores are vulnerable to grazing during persistent urchin foraging.
diagram from “The Oceans, Their Physics, Chemistry, and General Biology”, 1942

Consequences for Local Fisheries

Healthy red urchin roe
photo by D. Rudie

Coastal communities are already experiencing socioeconomic impacts from this environmental disaster. The recreational red abalone fishery and the commercial red sea urchin fishery are economically very important to the north coast region. The recreational abalone fishery was recently assessed at a value of $44 million to the fishermen (non-market value). The north coast sea urchin fishery, which mainly targets urchin roe for export, has been valued at $3 million (ex-vessel value) per year.

In 2015, the commercial red urchin fishery experienced a 66 percent drop in catch and economic value due to the poor quality of the urchin roe. Red urchins are the primary target of the fishery (not purple urchins) since they are larger and more marketable.

Shrunken abalone due to lack of food. The foot (meat) of the abalone should be roughly the same size as its shell. photo taken in Oct. 2015 by abalone fisherman S. Holmes.

Recreational divers and rock pickers reported shrunken and weakened abalone in fall 2015, which may also decrease the red abalone catch. Recreational abalone fishing on the north coast is a time-honored tradition, but people are less inclined to search for abalone if the meat is not worth the effort, or if people choose not to pursue abalone fishing due to concerns about the health of the resource.

CDFW Tracks Ecosystem Impacts

These rapid and dramatic changes over a large area of the coast are a primary concern for marine resource managers in California. Alerting the public, policymakers, scientific community and other stakeholders to these issues is a high priority for CDFW.

CDFW will prioritize research and monitoring of the situation to improve our understanding of the impacts hitting the affected fisheries, and to find methods that may help the kelp forest ecosystem recover. CDFW’s marine invertebrate management team is partnering with the fishing industry and the scientific community to identify opportunities to assess kelp forest recovery potential under various conditions. CDFW researchers will also continue the long-term ecosystem monitoring program that will track changes in ocean conditions, and hopefully the progress of kelp forest recovery.

Continued assessments of abalone health and reproduction on the fishing grounds will also improve researchers’ understanding of the magnitude of impacts to our fisheries. The CDFW Marine Region website and Marine Management News blog will be updated periodically with results and developments from these efforts as they occur.

What Can You Do?

Here are a few ways to become involved:

  • Share this blog post on your social media accounts. This is an important message. Please help spread the word!
  • Visit the Noyo Center for Marine Science’s “Help the Kelp” web page for the latest information about recovery plans and activities.
  • Report Observations: If you have observed related events, and would like to share your observations and photos, please contact CDFW’s marine invertebrate team. The most helpful information for research will include the date, location, and depth of your observations.

Download this article in a format suitable for printing (PDF)

Learn more:

Watch Dr. Laura Rogers-Bennett’s presentation “The Perfect Storm: Multiple Climate Stressors Push Kelp Forest Beyond Tipping Point in Northern California” (7/18/2019)
Fish and Game Commission Adopts Emergency Regulations to Increase Purple Sea Urchin Bag Limit in Sonoma and Mendocino Counties  CDFW Press Release (5/15/2018)
Listen to Dr. Cynthia Catton’s inteview about the closure of the north coast red abalone fishery on KZYX Mendocino Public Radio (12/21/2017)
California Recreational Red Abalone Fishery to be Closed in 2018  CDFW Press Release (12/08/2017)
Read Northern California Abalone Numbers Crashing, Recreational Season May Shutter by Santa Cruz Sentinel journalist Alex Fox (12/5/2017)
Listen to Dr. Cynthia Catton and sport diver Josh Russo’s interview on KRCB’s World Cafe program (11/7/2016)
Read North Coast Kelp Beds “Like a Desert” This Year by Santa Rosa Press Democrat journalist Mary Callahan (7/21/2016)
Watch Kelp Deforestation Threatening California’s Coastline
on CBS San Francisco Bay Area News (6/4/2016)
Read Collapse of Kelp Forest Imperils North Coast Ocean Ecosystem by Santa Rosa Press Democrat journalist Mary Callahan (4/16/2016)
Watch Dr. Cynthia Catton’s presentation to the California Fish and Game Commission on this topic (4/6/2016)
Listen to Dr. Laura Rogers-Bennett describe environmental impacts on KCBS News Radio

Harmful Algal Bloom
Abalone massacre pinned on microscopic coastal killer, SF Gate, May 2014
Abalone and Red Sea Urchins Die During Red Tide Bloom in Northern California, Marine Management News newsletter (pg. 4), October 2011

Scientific literature:
Forensic genomics as a novel tool for identifying the causes of mass mortality events, 2014
Dinoflagellate bloom coincides with marine invertebrate mortalities in northern California, 2012

Sea Star Wasting Disease
Current updates, information, & data:
Partnership for Interdisciplinary Studies of Coastal Oceans (PISCO)
Pacific Rocky Intertidal Monitoring: Trends and Synthesis
Scientists now link massive starfish die-off, warming ocean Seattle Times, February 2016
Scientific Literature:
Densovirus associated with sea-star wasting disease and mass mortality  2014

Urchin Barrens
Scientific Literature:
Sea urchin barrens as alternative stable states of collapsed kelp ecosystems  2014

Ocean Conditions
Strong El Niño sets the stage for 2015-2016 winter weather  October 2015, NOAA
Unusual North Pacific warmth jostles marine food chain  September 2014, NOAA
Web pages:
NOAA El Niño & La Niña (El Niño-Southern Oscillation)
Scientific Literature:
CalCOFI State of California Current  2015
Current and historic data:
CeNCOOS Data Portal
NOAA Climate Prediction Center

California Kelp Forest Fisheries
Abalone, CDFW Website
Sea Urchin, CDFW Website
Kelp, CDFW Website

Data: GIS Kelp survey data, CDFW, MarineBIOS
Maps: MarineBIOS (Biogeographic Information and Observation System), CDFW

Post by Cynthia Catton, CDFW Marine Environmental Scientist; Laura Rogers-Bennett, CDFW Senior Environmental Scientist Specialist, and Alisan Amrhein, California Sea Grant Fellow


63 thoughts on ““Perfect Storm” Decimates Northern California Kelp Forests

  1. So what is your proposal to do about this issue? I was at three different spots diving for abalone last Friday, Saturday and Sunday. Two spots had abalone with small meat. And the third spot had very very meaty abalone. I don’t think it’s a good idea to approach the fishery with a blanket after looking at four high frequency spots. The north coast has a lot of variability and monitoring since the 1990s is a small window in time compared to the tens of thousands of years the abalone have been here. With that said what would closing down the fishery do exactly? I hope this isn’t a power grab to justify more closures. If the lack of kelp is killing abalone is it possible for divers to finish the job? Also abalone don’t just eat kelp so please publish more information on the exact diets of abalone. Thank you for telling the whole truth and nothing but the truth so help you God.

    1. Thank you for your questions. The recreational red abalone fishery remains open on the north coast (Opening Day: April 1). CDFW will continue to monitor the health of the abalone resource as well as the environmental conditions that might limit future bull kelp recovery. These surveys will have broad spatial coverage to capture the variability along the coast and within sites. We will provide updates to the CDFW website and social media as more information is available.

    2. Abalone are algivorous. They feed upon marine algae of many species. Brown algae, which include kelps, red algae (many species), and green algae form the natural diet. Artificial foods are often used in culture. Sadly there is a bacterial disease called WS or withering foot syndrome which now infects native and aquaculture stocks of abalone throughout most of California. Pathologists with the CDFW and other labs are employing antibiotics to combat the disease in cultured abalone with improved success.

      1. Thank you for joining the conversation, Dave! Your long history and expertise with abalone aquaculture and kelp forest ecology is extremely valuable.

        Abalone eat a variety of fleshy seaweed in the wild, but we have observed reductions in all of these species in the kelp forest recently. Bull kelp is the foundation of the ecosystem and is of particular concern because it is an annual species.

      2. It would appear abalone on the northern coast are being impacted by scarcity of kelps and possibly other marine algae due in part to warmer water. Disease, notably WS, may also be exacerbated by higher than normal temperatures. WS has hit green abalone at the Carlsbad Aquafarm especially hard, killing almost all (many hundreds) of market-size abalone over the past five years. Any progeny from WS-infected broodstock have been grossly stunted. Macrocystis beds in southern California are currently in decline, apparently due to the warm water conditions. Sad state of affairs with declines kelps and diseases such as densovirus and WS RLO clobbering sea stars and abalone.

      3. The kelp forest and abalone dynamics in Southern California are pretty different from northern California. Giant kelp (Macrocystis) in Southern California is impacted by warm water and an invasive algal species (Sargassum horneri). Although sea star populations in Southern California were also impacted by the Densovirus, Southern California urchin populations contend with a suite of other predator species as well, including California sheephead (fish) and California spiny lobster. Withering Syndrome, which affects all abalone species, continues to be a threat to populations in Southern California. However, the disease agent has not yet spread to most of the areas within the abalone fishery in northern California. The shrunken animals we are observing in northern California are not succumbing to Withering Syndrome, but are showing signs of starvation.

    3. “Abalone don’t eat just kelp” you say? Aside from various species of red and brown algae – in addition to Nereoystis (Bull Kelp) – I was never aware of them consuming other items? If anyone knows of things other than algae abalone normally eat, please let us know. I have been studying abalone for 67 years now, and have written 76 papers on just family Haliotidae (the abalones). Any info one has on this, please pass it on.

      1. Sure you’re correct Buzz ! Abalone are herbivores and feed when young (postlarvae and early juveniles) on diatoms and other benthic microflora. As adults they feed on brown, red, and green algae.

  2. Thank you for the very informative article. This is my/our backyard and play pen. Understanding the conditions and ways we can help keep it healthy promotes stewardship and sustainability of our great natural community. Perhaps we should be looking for ways to harvest an use the purple urchin as a manageable resource. Urchin spine garden fertilizer? Urchin spine road asphalt? Urchin protein pet food? Urchin tooth paste? Just throwing it out there!

    1. Thank you for your comments and creative brainstorming. The commercial urchin industry has targeted purple urchins in the past, but only the larger ones, and during a short window of time when the roe is most developed.

  3. I have a question regarding water temperature. The article says bull kelp is affected by water temps over 63 degrees but the water temp in Northern California is in the 50s. Is this just a statement or a concern for some reason?

    1. During normal conditions, the seawater temperature on the northern California coast will not get warm enough to stress the kelp, averaging close to 53 degrees F. In the last two years, CDFW temperature records in the kelp forest have shown significantly increased water temperature, even at depths of 30 feet. A record high water temperature of 63 degrees F was recorded, which would impose substantial stress on the kelp forest. We are continuing to monitor the ocean and ecosystem conditions to track the recovery potential of the kelp forest.

      1. Where did the water temperature get above 60 degrees in Northern California, Redwood City? I have looked at NOAA records and it seems to average around 53 degrees. The highest recorded (54) I found was at Fort Ross, CA September through October 2016.

  4. If the kelp missed fertilzation by a natural proccess, why not mix an appropriate, organic fertilizer & strew it from boats off the coast? Ingredients might include kelp & cannery wastes. If high water temperatures throw the coastal marine ecosystem out of whack, why not lower tanks of liquid nitrogen to the seafloor at intervals, fasten them to anchored bouys, attach perforated tubes to the tanks & let cold nitrogen percolate up through the water? Kelp being a plant; would be fertilized by the nitrogen gas. Liquid nitrogen, in seawater-ice encrusted tanks, would lower average, continental shelf, seawater temperatures. Not a complete strategy, but perhaps effective parts of one i hope experts & other coast residents would plan, calibrate, & maintain.

    1. Thank you for your suggestion. Artificially changing ocean chemistry in the short-term to support kelp growth would be a very difficult task, with unknown consequences for the other species in the ecosystem.

  5. Thank you for these very insightful comments. I am a former urchin exporter from Maine and our kelp beds in Maine are flourishing since we cleaned up the urchins back in the 1990’s. There is still a small urchin fishery in Maine, which is enough to prevent any significant buildup of urchin biomass. We found juvenile sea urchins have a hard time settling and surviving in healthy kelp beds due to micropredators living in the understory or “shag carpet” as some call it. Lobsters are the prime beneficiary. Economically, lobster is more important to the state than urchins so the situation is a win for now. Lack of groundfish predation is a big part of the lobster boom, as well. We have seen urchin die-offs during especially warm summers and that could happen out there.

  6. If the abalone are starving to death why not allow more of them to be harvested? Thin out the herd so to speak allowing the ones that are left more to eat there by making the population healthier.

    1. The starvation conditions will persist even if the abalone population is “thinned” because urchin populations in the area are still very abundant. Removing more abalone will only provide more food to the urchins rather than to the remaining abalone. To address the overpopulation of urchins (particularly purple urchins), we are developing plans for targeted urchin population control to benefit the kelp forest and associated fisheries.

  7. Once again, as was the case with the invasive sargassum weed that’s wreaking havoc on southern kelp forests, CDFW has done nothing to prevent, or mitigate the situation except report on it once it’s a full-blown disaster! Thanks CDFW!

    1. Our ocean ecosystems are facing many challenges. We share your concern and are working diligently to track the changes as well as identify the most effective responses to these challenges. We are reaching out to many groups (government, academic, non-profit, and industry) and individuals to help us research, develop, and implement the needed actions to support recovery. We encourage you to get involved with this work by contacting Dr. Cynthia Catton at Cynthia.Catton@wildlife.ca.gov.

    2. T Baker – It is extremely difficult to learn that entire ecosystems worldwide are rapidly collapsing, especially when one of them is near and dear to us, to which we bare witness. However, I have learned that if we are expecting solutions, to any problems, to come from some source outside of ourselves, we will never solve the problems. This one is no different.

      We must find the courage to face the truth about global warming. It is human activity that has hurled planet Earth into her Sixth Mass Extinction Event. And of human activity around the globe, our American lifestyle of mass-consumption is the most destructive. The great news here is that we are more than capable of great change, as long as we take on the challenges in connection with others and focus our energy on the shared goal.

      In Peace & Gratitude,

  8. Thank you Dave Rudie for informing us on this issue! We sure appreciate all you do, to protect our ocean and all the critters that live in it! With understanding comes hope. Your our ocean super hero! 💙

  9. I’ve tried to copy this article to spread the news but this site will not let me – Why don’t you have a print selection under share this?

  10. I’ve been diving the the north coast since the 80’s I missed last year do to heath problems, I went Abalone diving in Mendocino last Monday and the visibility was fantastic but I was shocked the ocean looked like a desert. Hardly any bull kelp no star fish and the Abalone are hanging out on top of the reefs eating what’s left. the Abalone are definitely starving. This is so sad is there anything I can do

  11. Question/comment; why not encourage divers to spend a little extra time underwater smashing purple urchin?

    It seems that if an advertisement (similar to beach clean-ups) was made to a mass of people, we could all descend on a chosen area and irradiate a bunch of purple urchin. If nothing else, pick a control area and give it a go.

    1. Thank you for your enthusiasm! We are considering options for ways to effectively protect the remaining bull kelp and support greater kelp growth in strategic locations. We are currently working with the local commercial sea urchin fishery and other researchers to identify the most effective methods. If you are interested in helping us with our work, please contact Dr. Cynthia Catton (Cynthia.Catton@wildlife.ca.gov) for information on volunteer opportunities.

  12. Thankyou for your hardwork and dedication to the health of the intertidal environment.
    It’s not easy to deliver the message of the perfect storm, but your efforts are appreciated, and the educational news is valuable to understand.

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