Kelp in the Tacoma Narrows
As Puget Sound temperatures increase, bull kelp struggles to stay alive.
Between 2013 and 2018, researchers at the Washington Department of Natural Resources studied four bull kelp beds in south Puget Sound, comparing them with a bull kelp bed in the Tacoma Narrows. The group published their study in June.
The results weren’t reassuring.
All four kelp beds in south Puget Sound either died off completely or declined significantly. Lead researcher Helen Berry took a boat from Point Defiance Thursday morning to explain the implications of the study.
“The losses in south Puget Sound are alarming,” she said.
Kelp is an essential part of a water ecosystem. It helps create the conditions that make it possible for other species like salmon and orcas to flourish.
Kelp creates forest corridors along the shoreline, which juvenile salmon use to migrate. Adult salmon also use the corridors when they’re returning. Kelp also creates essential habitats for forage fish.
“When you start talking about those species, you immediately directly link to orca, which rely on salmon, and salmon rely on kelp beds,” Berry said. “When we think about kelp beds, I see the entire Puget Sound environment as part of that.”
In their study, the researchers focused on bull kelp, one of more than 20 kelp species in Washington state. Bull kelp makes an excellent subject for study because it stays closer to the surface of the water, making it easier to study than kelp that stays farther underwater.
Berry links the death of south Puget Sound kelp to warmer water temperatures.
Kelp needs cold waters to thrive. In warmer water conditions, bull kelp loses it blades and becomes “bald headed kelp.” Without blades, kelp can’t reproduce or photosynthesize.
Bull kelp normally loses its blades in the fall, Berry said. In the warmer conditions the researchers saw in the south Sound, the kelp began to lose its blades in midsummer.
“It’s clear it’s sensitive to climate warming,” she said.
Both El Nino and a warm water blob, essentially a large pool of warmer than normal ocean waters, have contributed to temperature increases in south Puget Sound since 2013, Berry said.
She added that the temperature in south Puget Sound has increased above 20 degrees celsius, which is the threshold at which kelp begins to experience physiological stress.
“That’s what we’re seeing recently and that’s a worldwide issue,” she said.
The Tacoma Narrows bull kelp beds the team analyzed didn’t deal with the same temperature increases or drastic losses as in south Puget Sound. Berry attributes this to water mixing, which she says lowers the water temperature in the Narrows.
“We measured record high temperatures in the kelp beds at those southern sites, whereas here in the Narrows, because there’s so much mixing, the temperatures remained much lower,” she said.
Higher water temperatures aren’t the only things which can hurt kelp survival. Berry said that sediment in the water, as well as other contaminants, can also harm kelp.
“Currently, the big water quality issue is urbanization that brings nutrients and more sediments and other pollutants,” she said.
People will have to modify the way they build in order to protect kelp and water ecosystems, said Hilary Franz, the Washington Commissioner of Public Lands.
“More clearing of the land upland from us creates more sedimentation,” said Franz, who tagged along on Thursday’s boat tour. “We need to have more people living within our already dense urban areas.”
She cautioned against expanding building projects far from urban centers.
“The more we’re moving farther and farther out and disrupting this ecosystem, we’re going to have significant impacts on our waterways and on the species that depend on it,” she said.
The next project for Berry and her team is an analysis of historical data to understand larger scale kelp death trends. They’re using early navigational maps of south and central Puget Sound to track bull kelp levels back over a hundred years.
Though the team has not yet completed the study, Berry said that results so far show that kelp has significantly decreased in the area, even in recent decades.
“Anecdotal information and our preliminary results show that in many areas we’ve lost a lot of bull kelp,” Berry said. “So 100 years ago and even in the 1980s there was a lot more bull kelp in South Puget Sound.”