Local giant kelp forests are threatened by warming waters, experts say
The waters off San Diego are home to the two largest kelp forests on the West Coast, and both are being closely watched by local experts who are concerned about the effects of climate change on the underwater groves.
The giant kelp forests off La Jolla and Point Loma are important to the ecosystem, said Ed Parnell, a researcher at the Scripps Institution of Oceanography in La Jolla whose studies focus on coastal ecosystems in Southern California.
“The giant kelp forest provides a habitat and food for a lot of different species that live there,” Parnell said.
Kelp grows and dies fairly quickly and includes “all different types of brown algae,” he said. “It includes the ones that float at the surface, what you see washed up on the beach.”
The kelp of the giant forests — which measure about 5 miles by about two-thirds of a mile at La Jolla and about 6 miles by 1 mile at Point Loma — typically lives less than two or three years, Parnell said, though it can live “up to about eight years. Nine years is the record for San Diego.”
“[The kelp] also puts out new tissue constantly … in the form of a stipe, or what’s called a frond. Each frond can live about six to eight months,” he said. “The plant is basically anchored to the bottom and is putting out these fronds, but then they get eaten, age, break off, whatever. But the plant continues to exist.”
To thrive, Parnell said, kelp is fueled by nitrogen in the ocean water. “Just like plants on land, you give them fertilizer,” Parnell said. “In the ocean, it’s nitrogen, in the form of nitrate.”
Climate change, however, and its effects caused by humans producing higher levels of carbon dioxide, or CO2, impacts the giant kelp forests in noticeable ways, he said.
“There’s a tight association between temperature and nitrate,” Parnell said. “If water gets too warm, there’s not very much nitrate, so kelps don’t grow. So above about 15 degrees Celsius [about 60 degrees Fahrenheit] bottom temperatures in the kelp forest, the kelps don’t have enough nitrate to grow and reproduce.”
While the current temperature “is really good for the kelp,” Parnell said, 2015-16 saw water that was much warmer, and “the kelp suffered mightily, [with] almost complete die-off.”
The implications associated with warm water and kelp forests disappearing, Parnell said, are a “series of die-offs of sea urchins and sea stars. There’s been a very big disturbance to that community in terms of loss of giant kelp, many of the sea stars and loss of some sea urchins in some areas.”
There was “less food and less habitat over time up until about 2017, when it started to grow again,” he said.
Though the kelp appears to be growing now in cooler water, Parnell is watching long-term threats.
In the late 1970s, he said, there was a “regime shift” — rapid, persistent change — with “a bump-up in temperature” in the water off Southern California.
Before that, Parnell said, kelp off Southern California had enough nitrogen, except for the most extreme El Niños, or periods when there was warm water and few nutrients. After the shift of the late ‘70s, “what happened was you went from a period where nutrients were replete most of the time to a period now where nutrients are only OK during strong La Niñas [cooler water and lots of nutrients] and neutral periods.”
“What’s happening is kelps over time are going through warming events getting more severe, so grow periods are decreasing in terms of their length and their frequency,” Parnell said.
Extrapolating that pattern forward, Parnell said, the giant kelp forests “growing off San Diego [are] going to decrease more and more.”
At the current rate, forest depletion will “be a gradual thing. How quickly it’ll happen is not clear,” he said.
“If you go to central Baja, the kelp forests are only there when there’s a really, really cold year,” Parnell said. “Otherwise, there’s almost no kelp. That’s what they’ll look like here eventually.”
Parnell also points to the dearth of kelp off Tasmania. “There used to be very lush kelp forests there,” he said. “But over the last 20 years, there have been changes in the temperature structure of the water, and that has led to almost no kelp now.”
On a small scale, “there’s nothing we can do about it,” Parnell said. “We’ve set up marine protected areas, but that’s not going to make the kelp grow. On a large scale, we definitely affect our climate by our CO2 emissions, so it’s more important than ever to reduce our carbon footprint in terms of keeping the warming as low as possible.”
Carly Kupka, lead of the climate change committee at Surfrider Foundation San Diego, a nonprofit environmental organization, said she’s working to save the giant kelp forests and other coastal features threatened by climate change.
Kupka, an avid paddleboarder who often peers down at the forests from above, said: “The kelp forests are amazing. They’re an entire ecosystem; we’re talking seals and fish … all these things that make San Diego’s coasts really unique and biodiverse. ... So if you take away this habitat, you’re going to lose all these things.”
Kupka said her committee’s efforts focus on “pushing for policy in our local communities” to mitigate the impact of climate change in San Diego. “We’re advocating for reduction in CO2 emissions,” Kupka said.
“We focus on ... things like renewable energy. The more we do that, the more we can curb the effects of global warming and hopefully reduce the ocean’s warming and the dying off of kelp.” ◆
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