Exploring Puget Sound's Kelp Forests

Beneath the water’s surface, a world of kelp pumps life into Puget Sound. Over 20 native kelp species occupy the intertidal and subtidal depths (1), helping to foster the rich marine biodiversity and ecosystem health that supports our Pacific Northwest way of life, and our coveted seafood cuisine. Similar to a terrestrial forest, this diverse assemblage of understory and canopy kelp species creates a living, 3-dimensional space and complex ecosystem - or an “underwater forest.”

Bull kelp (Nereocystis luetkeana) is an iconic species that helps form these extensive underwater forests in nearshore, rocky habitats. As an annual macroalgae and one of the primary species of canopy-forming kelp, bull kelp emerges each spring and grows to create forest-like structures that can stretch up to 40 meters (2). The bulb and blades reach toward the water’s surface and a holdfast remains anchored to the sea floor. Just like the forests above, our kelp forests below are vital -- not just as one of the most ecologically productive habitats on the planet (1) -- but as lifelines for crab, salmon, killer whales, and us.

Very little is known about changes in distribution and abundance of many understory kelp species(2), but significant declines of bull kelp have been documented in parts of Puget Sound through ongoing surveys, anecdotal evidence and observations. For example, historical kelp beds along the shores of Bainbridge Island have been lost entirely (1), and upwards of 80% of this key habitat has been lost in South Puget Sound (3). To build support for kelp conservation and recovery, we need to connect the dots between kelp and us. Communities and cultures of the Pacific Northwest have been nurtured by healthy marine systems for a long time; when a foundational piece of our social and ecological systems begins to unravel, we need to join hands and take a leap toward collective action.

Bull kelp has played a particularly prominent role in traditional ecological knowledge and technology. The versatile structural material of bull kelp - including the holdfast, stipe, float, and fronds - has been used by Pacific Northwest Tribes to create hunting and fishing tools, food storage containers and other household items, and toys and games for both children and adults (4).

As kelp matures and grows, kelp blades release dissolved organic matter (DOM) that is consumed by bacteria and plankton, which in turn feed our favorite filter feeders - such as oysters, clams and mussels (13;14;15;16).

The tips of the kelp blades also naturally erode - leaving small particles, called kelp detritus, to float away (13;17).

Kelp detritus is a primary food source for a large community of marine invertebrates including shrimp, copepods, amphipods, and isopods, many of which are important prey for pacific herring, other forage fish, juvenile salmonid, and young-of-year rockfish (1;13;14;16).

When kelp naturally breaks away and begins to decompose, the material drifts to the bottom and serves as a seafloor buffet for a variety of benthic invertebrates and scavengers, such as crabs, sea urchins and abalone (13;18).

Many of these smaller kelp connoisseurs are food sources for highly-coveted recreational and commercial fish species, such as salmon and lingcod (19;20).

Kelp detritus that drifts further away provides food to adjacent marine food webs and deep-water habitats far from the nearshore (1;17).

Detached kelp material also washes ashore to create what are called “kelp wracks” along the high-tide mark, where insects and other terrestrial invertebrates, along with scavengers such as birds and raccoons, enjoy a shoreline feast before carrying the kelp carbon onward into upland food webs and beyond (1;21).

Anchored to the seafloor and reaching to the water’s surface, kelp forests form a three-dimensional, structured habitat. This living habitat is critical marine infrastructure supporting the extraordinary biodiversity that defines the Puget Sound waters we know, love and depend on.

Pacific herring, a forage fish that many larger species seek for food, spawn directly on the floating and submerged kelp fronds (1). The tiny eggs are a delicacy for birds and other prey; after hatching, the larvae remain in nearshore waters close to their spawning grounds to feed and grow in the protective cover of shallow water and kelp structure (13;22).

Out-migrating juvenile salmon seek shelter in the kelp canopy and shallows, while adult salmon - including coho and chinook - patrol the fringe in search of prey (1;13)

Endangered rockfish - like the bocaccio - rely on this critical nursery habitat that allows them to feed in relative safety from predators (1;13).

Birds and marine mammals look to these food-filled kelp forests for their next meal, or sometimes even for a nap.

Even Puget Sound’s iconic Southern Resident killer whales know to hunt for prey in and along floating kelp beds.

From the kelp carbon in the fish and shellfish we eat, to kids playing on the beach with bull kelp stipes, these marine forests are vital to our food chain, and central to our local culture and identity. In other words, kelp is integral to our sense of place.

Many fisheries we depend on are tied to the health of kelp forests. And anyone who fishes knows that kelp forests are where the salmon and rockfish can be found.

“I picked a slot between rafts of kelp and cast out...when I was just about to lift it out of the water to try another cast, the water exploded...my Rotator headed for Port Townsend in the mouth of yet another magnificent coho.” - A Puget Sound Angler

The dense beds of floating kelp fronds can help to protect our beaches and shorelines by absorbing wave energy that can cause coastal erosion and subsequent beach loss (1).

Through photosynthesis, kelp forests fix or store more excess carbon than tropical rainforests, seagrasses, and even coral reefs. In Washington state alone kelp forests uptake 27 to 136 metric tons of carbon per day, which is equivalent to the emissions of approximately 2,000 to 10,500 vehicles per year (1).

While kelp forest presence is highly dynamic over time, Sound-wide surveys - like those to the right - highlight dramatic downward shifts in bull kelp presence between 1978 and 2000.

Though some floating canopy kelp forests (Nereocystis and Macrocystis) appear to be doing well along the western Strait of Juan de Fuca and parts of the San Juan Islands, the Samish Indian Nation estimates a 36% decline - a loss of 305 acres - in bull kelp forests around the San Juan Islands between 2006 and 2016 (25). Dive deeper into bull kelp loss in the San Juan Islands  here .

While the total floating kelp canopy area along the eastern Strait of Juan de Fuca has been stable over the last 30 years overall, canopies [are highly variable from year to year and] appear to be contracting in some areas. (26;27).

In the Central Sound, bull kelp beds around Bainbridge Island have disappeared entirely, with the last forest off Wing Point blinking out in 2015 (1).

In the South Sound, the linear extent of bull kelp between 2017 and 2018 was 80% less than the cumulative total of all observations from the last 145 years (3). Squaxin Island is home to one of the last remaining persistent bull kelp forests in the South Sound; but a recent study shows that it, too, is in decline. Following an increase in water temperature caused by a marine heatwave in 2014, the study outlines the visible loss of the bull kelp forest in both total extent and depth distribution. Some areas that experienced similar levels of decline rebounded quickly, while others (like Squaxin Island) have yet to recover. Other bull kelp forests disappeared entirely and have not returned.

Explore further data and trends of South Sound bull kelp decline  here .

Though definitive causes for such unprecedented declines are uncertain and vary by geographic location, researchers and scientists are making active strides to understand the kelp loss in Puget Sound. Fortunately, bull kelp has not disappeared entirely from any of Puget Sound’s basins. It still remains common in areas with intense currents and water mixing, such as the Admiralty Inlet and Tacoma Narrows, shown in the image below. Areas with similar conditions may serve as refuges for bull kelp from some of the stressors that are leading to losses in other areas of Puget Sound (3;28).

Research indicates bull kelp forest decline is likely due to the following stressors and their interactions:

• Deteriorating water quality, which can mean excessive pollutants and nutrients from runoff (1)
• Increasing seawater temperatures (1)
• Increased grazing of kelp by invertebrates due to shifts in the marine food web. For example, urchins can “clearcut” entire kelp forests if left unchecked by predators (1).
• Competition from invasive seaweeds, such as Sargassum (Sargassum muticum)  (1)
• Increasing water turbidity and sedimentation, which can inhibit photosynthesis (1)
• Compounding effects of multiple stressors (1)

Climate change further exacerbates these significant challenges and uncertainties. Circling back to the heatwave of 2014, evidence suggests that the combination of rising water temperatures and seastar wasting disease resulted in the decimation of bull kelp forests along the Northern California Coast (1;29). Free from predation by sunflower seastars, sea urchin populations exploded, and their unchecked grazing has created "urchin barrens” almost devoid of bull kelp and other kelp species. These cascading effects not only impact the marine ecosystem, but also the associated fisheries that communities depend on (29).