Turns Out Undersea Kelp Forests Are Crucial to Salmon

[CLIP: Walking on pebbles]

Starre Vartan: I love a short cold-water swim in Puget Sound in Washington State. I start from a rocky shore near my home.

[CLIP: Walking, splashing farther into water and diving]

Vartan: If I kept swimming just another 100 feet out, I could dive a few feet down through these clear waters into an underwater forest where animals such as shrimp, crabs and small fish like lingcod, rockfish—and maybe even salmon—like to live.

[CLIP: Diving sounds]

Vartan: This is Scientific American’s Science, Quickly. I’m Starre Vartan.

Kelp forests are made up of thick, undulating ribbons of brown algae that hang on to rocks at the seafloor and grow toward the light above.

Kelp is found in dense groups, like trees on land, hence the name “forests.”

But just like forests on land, lately these underwater forests have come under threat from climate change.

The kelp forests off California’s coasts have largely disappeared in recent years. It all started in 2013 with a mysterious “blob.”

That’s what scientists called this blobbish patch of warmer-than-normal ocean water, which was created by changes in the atmosphere above the Pacific.

The blob brought drastic changes to the California kelp forests. Elevated ocean temperatures led to a die-off of sea stars.

Sea stars typically control the population of sea urchins. Sea urchins eat kelp.

And so the coming of the blob created an explosion of urchins. The creatures went on an eating spree that, by some estimates, cleared 96 percent of the kelp from beneath the California coast.

Up north, Canadian Pacific kelp forests have also been stressed and shrinking.

For now, the forests in Puget Sound, where I live, are intact in some regions but not in others. That means there’s both time to research kelp’s importance and to try to save it.

[CLIP: Kelp forests underwater]

Vartan: A healthy kelp forest, which you just heard, is typically a quiet safe haven. They provide complex habitat to hundreds of species, including benthic invertebrates, small fish and animals all the way up the food chain to gray whales. Sea otters twist their bodies into the kelp. That way they can sleep without drifting and wake to breakfast a forepaw’s swipe away.

Forests of kelp dampen wave energy and create a physical refuge for marine life. They also store so much carbon that scientists call them the “sequoias of the sea.”

Like terrestrial forests, they also bolster oxygen via photosynthesis and absorb carbon dioxide. In the sea, that reduces acidification that kills more vulnerable marine animals.

There are so many benefits—and recently a newly verified one: salmon, those Pacific Northwest icons, also use kelp. Fishers had previously said this was the case, and so did Anne Shaffer, a marine biologist with the Coastal Watershed Institute in Washington State. She’s studied kelp forests for more than three decades.

She remembers from a few years ago …

Shaffer: A biologist with the state who blurted out, “Well, salmon don’t use kelp forests.” And, you know, my immediate retort was “Except when they do.”

Vartan: So she set out to prove it.

I met with her about 10 miles up the coast from her HQ in Port Angeles, Washington, on the coast of the Strait of Juan de Fuca. We hiked out to the mouth of the Elwha River, where Anne does some of her research into kelp forests.

A little more than 10 years ago the Elwha had two dams that prevented salmon migration. But now the river flows free, and it has created acres of new beach habitats and enriched the underwater ecosystems, too.

[CLIP: Elwha River flowing into the Strait of Juan de Fuca]

Shaffer: This is the mouth of the Elwha. And what happens is the water comes out of the Elwha river, comes into Freshwater Bay, and then there’s a big gyre that forms right here. And so basically what happens is this plume of Elwha water will circle around right into that kelp bed where surveys are.

[CLIP: Walking along the sandy and rocky shore]

Vartan: Anne and her team, including undergraduate students, have spent more than seven years taking snorkeling surveys of who uses the kelp forest here.

[CLIP: Young kelp researchers audio]

She’s found that it varies seasonally. Her research, published this year, showed that several types of endangered salmon, including Chinook, coho, chum and pink salmon, definitely use kelp—in multiple ways.

Shaffer: So juvenile salmon, juvenile forage fish, as they’re migrating along the shoreline, they’re their areas of refuge. And they also provide a nursery ground so these animals can rest and feed because they have the richer zooplankton communities and grow and then get ready for these bigger transitions to offshore and different habitats.

Vartan: Specifically the type of zooplankton the salmon found in kelp was different.

Shaffer: There were these few key species of what are called vitally associated invertebrates, and those are the ones that are associated with kelp, and those are also the ones that are very highly selected for by juvenile salmon and forage fish.

Vartan: But as they grow, the salmon can also use the kelp to prey on smaller fish, too.

Shaffer: Salmon will actually herd their prey. These little guys, little juvenile salmon, will herd their prey up into a ball and then just slam them, and they’re able to make them ball up like that because of the kelp. It acts as, basically, like a barrier or a net.

Vartan: Salmon are incredibly important in the Pacific Northwest. Northwest tribes have had a practical and spiritual relationship with them for thousands of years. They feed people and the critically endangered southern resident orca population. This is a genetically distinct group of around 75 killer whales that only eat fish. These orcas often struggle to find enough to eat in local waters.

If you live in the Pacific Northwest, you know that when orcas and salmon are involved, lawmakers, government agencies, tribes and many others take notice.

And this is why it was so important for Anne to prove that salmon were using the kelp forests.

There was already some dedicated interest in protecting kelp habitats for the many other ways they are important, but now that salmon are involved, even more people will be paying attention to their conservation.

Shaffer: The forage fish and salmon story is bigger than just the kelp forest, and the kelp forest component to it is a really complex one.

Vartan: Anne believes there is a lot more research that needs doing.

Shaffer: When I first came back to Washington, I was just confounded at the fact [that] nobody was looking at the kelp forests. People were looking at eelgrass really heavily at that time, and kelp was an afterthought.

And so that was really what was driving my compulsion to study this for so long. Now people have really shifted and are really starting to look at it, so now is really the time.

Vartan: A number of studies are ongoing. The Puget Sound Restoration Fund is currently running what is the most in-depth monitoring program of kelp forests in the world. Understanding what specific factors are causing the variability in kelp forest health here will hopefully prevent what happened in California.

Back at the rocky shore of Puget Sound in late autumn, the sun cheers me into plunging into 50-degree-Fahrenheit waters. As I skim along the surface of the sound, I imagine the forests below, sun glinting off their waving brown-green blades, and the fish and almost-microscopic creatures snug in their ebb-and-flow home. I hope they stay healthy for all our sakes.

Science, Quickly is produced by Jeff DelViscio, Tulika Bose, Kelso Harper and Carin Leong. Follow Scientific American for updated and in-depth science news.

For Scientific American’s Science, Quickly, I’m Starre Vartan.

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