Top Line: Kelp forests are extraordinarily important concentrations of biodiversity and are extremely threatened, along the Oregon coast and around the world.
Figure 1. Rockfish in a forest of bull kelp. Source: Steve Lonhart, NOAA.
For most people, to see a forest is to love a forest. However, few have ever seen or will ever see a kelp forest. They can be seen from above by satellites, airplanes, and drones, and in the ocean if one is wearing scuba gear, but the closest most people will get is coming across some dead kelp washed up on the beach after a storm.
Figure 2. Bull kelp washed ashore after a storm. Source: Steve Lonhart, NOAA.
Kelp forests are extraordinarily important centers of biological diversity, even more so today, when they are in severe decline. Algal kelp forests and coral reefs combined cover only 0.1 percent of Earth’s total surface but account for 0.9 percent of global primary production (aka photosynthesis and chemosynthesis). Kelp forests are declining globally at a rate of ~2 percent annually due to ocean warming and heat waves, other climate-driven stressors (ocean acidification and increased storm intensity), overfishing and kelp harvesting, and pollution and eutrophication. Along the Oregon coast, kelp forests are in trouble for many of these reasons—and more.
Kelp Forests of the World and Their Ecological Functions
Kelp forests range along approximately 25 percent of the world’s coastlines and grow best in cold, nutrient-rich waters. Currently, 112 species of laminarian kelp in 33 genera have been identified. A disproportionate share of the world’s kelp forests is found along the coasts of the northern Pacific Ocean from Japan to Mexico.
Figure 3. Kelp forests of the world by major types. Source: Wernburg et al. 2019.
According to the 2024 Oregon Kelp Forest Status Report published by the Oregon Kelp Alliance (ORKA):
Kelps are typically defined as large, brown seaweeds in the order Laminariales. Kelp forests are shallow (<30 m) marine ecosystems that form on rocky coastlines in the presence of kelps, usually in sub-polar to temperate waters. They are widely distributed coastal ecosystems lining an estimated 24% of the world’s coastlines. Similar to trees in terrestrial forests, kelps are ecosystem engineers that provide extensive habitat and food, which attract a wide variety of other species. Kelp forests also provide a wealth of ecosystem services that benefit human communities, including supporting diverse fisheries, buffering coastlines from storms and waves, creating opportunities for recreational and cultural activities, transforming large amounts of carbon into organic material, and oxygenating and de-acidifying ocean waters locally. [citations omitted and emphasis added]
Figure 4. The 2024 Oregon Kelp Forest Status Report, recently published by the Oregon Kelp Alliance. Source: Oregon Kelp Alliance.
The ORKA report goes on to note that in what is today known as Oregon,
[K]elp forest ecosystems have existed along the coastline since time immemorial. For much of Oregon’s history, these productive ecosystems supported a suite of iconic species, including sea otters (Enhydra lutris), gray whales, red sea urchins, multiple species of abalone, and several species of groundfish such as rockfish, lingcod (Ophiodon elongatus), and cabezon (Scorpaenichthys marmoratus). Kelp forests are known to be particularly important habitat for juvenile fishes. Historically, Oregon’s kelp forests provided rich nursery habitat for diverse fish species, including rockfish and likely salmon (Oncorhynchus spp.). Recent work has also tied gray whales to kelp forests. The zooplankton communities these whales prey upon are found in increased concentrations in kelp forests. From tiny fish to mighty marine mammals, kelp forests have been powerhouses of nearshore diversity and productivity along Oregon’s wave-tossed shorelines for millennia. [citations omitted and emphasis added]
Figure 5. A still image of a gray whale foraging in the midst of a kelp forest at Cape Foulweather, Oregon, in 2023, from a video captured by a drone. Look carefully slightly right of center to see the whale spouting. Source: Sara Hamilton, Oregon Kelp Alliance.
Indeed, offshore Oregon is home to more than twenty-five species of rockfish. They are long-lived, with some reaching a century in age. They can range from a foot to more than three feet in length. Rockfish require rocky reefs and kelp forests.
Figure 6. Redbanded rockfish. Source: Ed Bowlby, NOAA.
Kelp Forests in Dramatic Decline
Kelp forests are in trouble, the ORKA status report notes:
Kelp forests are highly dynamic but are experiencing a net decline globally due to the impacts of localized human activities, such as overfishing and water pollution, as well as the various impacts of global climate change. Over the past decade, kelp forests have severely declined in several regions along the West Coast of North America, from Baja California to the Aleutian Islands. The severity, spatial scale, and drivers of these declines vary from region to region. In Northern California, marine heat wave events, the vast expansion of kelp-grazing sea urchins, and the recent loss of a sea urchin predator to disease drove a widespread, synchronous collapse across several hundred miles of coastline. Conversely, in Washington state, trends in kelp forest cover can vary over relatively small spatial scales (tens of kilometers) and losses are thought to be connected to long-term ocean warming, sedimentation, and nutrient pollution rather than to trophic dynamics. [citations omitted and emphasis added]
What about Oregon? When offshore Oregon kelp—of either the bull (Nereocystis luetkeana) or giant (Macrocystis pyrifera) variety—reaches the surface of the water and is visible to humans not in the water, it has formed a canopy, somewhat similar to an onshore forest canopy that reaches toward the sky. Measurements of this canopy over recent years indicate that kelp forests are in severe decline along the Oregon coast. ORKA’s 2024 Oregon Kelp Forest Status Report tells us:
Overall, aerial survey data estimates that from Cape Arago south to Brookings there was a 66.4% decrease in kelp forest canopy from 2010 to 2022, and satellite-derived data covering the entirety of Oregon’s coastline estimated a similar decline of 73.5% from 2010 to 2022. [emphasis added]
Elsewhere, the report tells us the amount of the decline from 2010 to 2022 was 892 acres. (One acre is the area between the five-yard lines of an American football field.) Some simple arithmetic shows there were 1,214 acres of offshore Oregon kelp forest in 2010 and 322 acres in 2022.
Figure 7. Change in kelp canopy cover offshore Oregon from 2010 to 2022 as measured by either satellite or plane observations. Source: Oregon Kelp Alliance, 2024 Oregon Kelp Forest Status Report.
What about before 2010? ORKA’s report says:
Little data on kelp in Oregon exists in the historical record from the late 1800s through the 1980s, although Oregon-wide surveys were conducted in 1911 and 1954 to assess the extent of bull kelp. Generally, these early surveys show a distribution of kelp forests along the Oregon coast that is similar to the distribution of kelp over the past several decades, but the infrequency of these historical surveys and differences in documenting methods and data make deeper insights difficult to gather from them. [citations omitted and emphasis added]
Figure 8. Each area’s share of Oregon’s pre-2010 kelp forest canopy. Source: Oregon Kelp Alliance, 2024 Oregon Kelp Forest Status Report.
From what is known, it appears that offshore Oregon kelp forest levels were stable (with natural variation) in the twentieth century. How much was there prior to European settlement? We really don’t know. We really do know we have a serious problem in this twenty-first century.
A Closer Look at Kelp Along Oregon’s Rocky Shores
Oregon’s coastline from the California border south of the mouth of the Winchuck River to the mouth of the Columbia River measures 362 miles, of which ~262 miles are sandy shores and ~100 miles are rocky shores. Kelp forests are strongly associated with rocky ocean-floor substrate—for us landlubbers, a type of ocean floor well correlated with islands, rocks, and reefs near shore, of which there are more than 1,400 above high tide along the Oregon coast. At the extreme of expanses of sandy shore are the greater Oregon Dunes from Coos Bay to north of the Siuslaw River; no islands or kelp forests are found offshore this stretch of coast.
Along Oregon’s 100 miles of rocky shores, there was in 2010 an average of 12.4 acres of kelp forest per mile and in 2022, 3.2 acres per mile. If that kelp forest were evenly distributed (it’s not) along those 100 miles of rocky shores, the forest would have had an average width of 100 feet in 2010 and 27 feet in 2022.
Figure 9. Extent of kelp forest at Blanco and Orford Reefs, Oregon, in 2010 and 2022. Source: Oregon Department of Fish and Wildlife.
Figure 10. Extent of kelp forest at Rogue Reef, Oregon, in 2010 and 2022. Source: Oregon Department of Fish and Wildlife.
Figure 11. Extent of kelp forest at Redfish Rocks, Oregon, in 2010 and 2022. Source: Oregon Department of Fish and Wildlife.
One Big Driver of Oregon’s Kelp Forest Decline: Trophic Dynamics
Food chains or food webs within ecosystems have three basic levels: producers, consumers, and decomposers. These three levels must be kept in balance to maintain the health and function of an ecosystem. Offshore Oregon kelp forests are severely out of balance in terms of their trophic dynamics, with sea urchins, abalone, sea stars, and sea otters all playing positive or negative roles.
In the early 2010s, explains the ORKA report,
a perfect storm of interacting conditions negatively impacted kelp forest ecosystems across the entire West Coast of North America. From 2014–2016 this region concurrently experienced intense and sustained marine heat waves, sea star wasting disease, and dramatic increases in purple sea urchin populations. Beginning in 2013, sea star wasting disease began decimating populations of sunflower sea stars, large predatory sea stars that can help control sea urchin populations through predation. Around the same time, a historically severe marine heat wave caused extremely high nearshore ocean temperatures that persisted for years and that were likely beyond safe temperatures for kelps in many places, preventing successful growth and reproduction. Finally, massive increases in purple sea urchin populations overgrazed standing kelp forests and prevented new kelp from establishing in the coming years. Across hundreds of miles of Northern California coastline, researchers documented the collapse of bull kelp forests beginning around 2015. This collapse has persisted to the present.
Evidence of similar changes in Oregon’s kelp forests has been slowly accumulating since 2015. For instance, sunflower sea star populations were reduced by 99% in Oregon. ODFW documented a 10,000% increase in purple sea urchin populations at long-term monitoring sites along Oregon’s south coast. Red sea urchin divers were forced to abandon prime historic fishing grounds such as Orford Reef due to a loss of kelp and poor quality red sea urchins resulting from limited food supply. The small, largely recreational abalone fishery in Oregon was closed as abalone populations began to decline in response to food limitation. Loss of kelp forest habitat in two sites near Port Orford has been connected to a decline in gray whale prey abundance and a subsequent decline in gray whale foraging at those sites. [citations omitted and emphasis added]
Figure 12. Red abalone, a species in decline along the Oregon coast due to food limitation. Source: NOAA.
Sea Urchins: Excessively Colorful
At one time red sea urchins, which have a commercial market mostly for their roe, were found primarily in deeper water, and purple sea urchins were found primarily in intertidal pools. Now the population of purple sea urchins, which graze on kelp forests, has ballooned out of control due to a lack of predators such as abalone and sea otters and is preventing the recovery of kelp forests. Common now are “urchin barrens,” areas barren of kelp that are initially anything but barren of purple sea urchins until the urchins themselves begin to starve and die.
Figure 13. Close-up of a purple sea urchin barren, barren of kelp. Source: UC Santa Barbara Multi-Agency Intertidal Network.
Where Have All the Sunflowers Gone?
In 2013, scientists first noticed a decline in sunflower sea stars (Pycnopodia helianthoides), a species that can reach up to one meter across and have up to twenty arms colored orange, red, purple, or beige. Sunflower sea stars can be found to a depth of 1,400 feet but mostly live in waters less than 120 feet deep, and range from the central Aleutian Islands to Baja California.
Figure 14. Sunflower sea star, a species in severe decline due to a lethal pathogen. Source: NOAA.
By 2017, more 90 percent of members of this species were gone. A lethal pathogen, as yet unidentified, causes sunflower sea stars to become lethargic, develop lesions, lose their arms, and—within days—disintegrate into a gooey mass. While many sea star species are affected, sunflower sea stars have gotten the worst of it. The pathogen is linked to stressors such as decreased pH (more acidic seawater caused by the ocean absorbing increased atmospheric carbon dioxide, primarily from the burning of fossil fuels) and pollution.
Sunflower sea stars prey upon urchins, be they purple or red. When urchins no longer have predators feasting on them, urchins feast on kelp, eventually destroying the kelp forest.
Fortunately, sunflower sea stars are not extinct, and a very slow recovery appears to be happening.
Bring Back Those Sea Otters
A vital part of the long-term conservation of kelp forests offshore Oregon is to bring back the sea otter. No ecosystem should be bereft of its top predator, and the long-term survival of kelp forests depends upon otters once again regularly dining on sea urchins and abalone. Sea otters eat grazers that graze on kelp and sea grass. Sea otters need kelp forests, and kelp forests need sea otters.
See Public Lands Blog post: “Bring Back the Elakha.”
Figure 15. Oregon used to have sea otters. Oregon needs to have sea otters. Oregon can have sea otters again. Source: Wikipedia.
What You Can Do to Help
Besides advocating/agitating to (1) reverse human-caused climate change, and (2) designate additional marine protected areas, you should also send a contribution to the Oregon Kelp Alliance, which is a project of The Ocean Foundation. They are doing great work on a small budget.
Figure 16. Another take on the presence (blue-green dots) or absence (gray dots) of kelp forests offshore Oregon, in 1984. Source: kelpwatch.org.
Figure 17. Another take on the presence (blue-green dots) or absence (gray dots) of kelp forests offshore Oregon, in 2024. Source: kelpwatch.org.
Bottom Line: Kelp forests can return if human-caused irritants are removed and judicious human-assisted restoration is undertaken.
For More Information
Eger, Aaron M., et al. 2022. Kelp Restoration Guidebook: Lessons Learned from Kelp Projects Around the World. Arlington, VA: The Nature Conservancy.
Frankowicz, Katie. December 8, 2024. “New Report Shows How Oregon’s Kelp Forests Have Dwindled.” Oregon Public Broadcasting.
Hamilton, Sara, et al. 2024. 2024 Oregon Kelp Forest Status Report. Oregon Kelp Alliance.
kelpwatch.org. World’s largest dynamic map of canopy-forming kelp species (extremely cool interactive map).
Monterey Bay Aquarium. Bull Kelp (web page).
———. Purple Sea Urchin (web page).
Oregon Department of Fish and Wildlife. Rockfish (web page).
Oregon Kelp Alliance. Sunflower Sea Star Recovery (web page).
Palenova, Elena. June 16, 2018. “Here Are 11 Common Sea Stars (Starfish) Found on Oregon’s Coast.” OregonLive/The Oregonian.
Trees Foundation. Bull Kelp (web page).
Wernburg, Thomas, et al. 2019. “Status and Trends for the World’s Kelp Forests.” Chapter 3 in World Seas: An Environmental Evaluation, 2nd ed. New York: Elsevier.
Wikipedia. Kelp Forest (web page).
———. Sebastes (aka rockfish) (web page).
Wozniacka, Gosia. 2024. “Oregon’s Underwater Forests Are Vanishing. Can They Be Saved?” OregonLive/The Oregonian.
Zuckerman, Catherine. May 26, 2023. “The Vanishing Forest.” The Nature Conservancy magazine.
Figure 18. Kelp forest offshore the southern tip of Cape Arago, Oregon. Source: Oregon Kelp Alliance.