Patagonia’s coast offers a cool haven for giant kelp

Most coastal kelp forests around the world are struggling with climate change, but part of Patagonia’s kelp forest is thriving. Its success is due to the cold spells at sea, according to a new study in AGU’s Journal of Geophysical Research-Oceans. Credit: NOAA

Gigantic kelp forests around the world have struggled to stay healthy in recent decades, and some have completely disappeared. But along Patagonia’s rugged southwestern coast, giant kelp thrives and shows remarkable stability for: almost 200 yearsNew research suggests frequent cold spells of sea kelp can keep kelp happy.

The researchers found that the southwestern giant kelp forests haven’t experienced an extreme marine heat wave since 1984 and that the area has, in fact, experienced regular marine cold spells that intensify. From 2014 to 2019, the region saw more severe and extreme cold spells than during the rest of the study period. Glacier melt and increased wind activity could explain these rapid, localized cooling events.

Giant kelp forests are found it along a quarter of the coastlines from the equator to the high latitudes, and are critical species to their ecosystems, belonging to the world’s most productive and biodiversity. Heat waves can cause changes in what other species are nearby, such as sea urchins and the sea otters that snack on them in the Northern Hemisphere; if the otters disappear, hedgehogs may overgraze the kelp forests. High sea temperatures can also stress the kelp directly, as they are best suited to cooler waters. In central and northern Chile, unregulated direct to harvest is by people devastating kelp forests. These threats have demoted many kelp forests over the decades and have led to losses of 2% of kelp forests per year.

Yet the gigantic kelp forests of Patagonia, at the southern tip of Chile, look just like they did in the early 1900s, according to marine geographer Alejandra Mora-Soto, lead author of the new study, which was published today in AGU’s Journal of Geophysical Research-Oceans. In her previous workMora-Soto compared nautical charts as far back as Charles Darwin’s Beagle expedition to modern satellite imagery of kelp and found that little had changed, despite climate change and human influence.

“It’s a very persistent ecosystem, so the question was, ‘Why has this particular kelp forest been around for so long?'” said Mora-Soto, who is currently affiliated with the University of Victoria in British Columbia, but completed this research while she was working. worked at the university. from Oxford.

To find out, Mora-Soto and colleagues analyzed the sea surface temperature of the southernmost 800 miles of South America’s coastline from 1981 to 2020. They looked for marine heat waves and cold periods† As heat waves highlight the kelp forests, they wondered what impact cold spells have.

“The melting of glaciers means more cold water is entering the ocean. This can lead to very short spikes in cool temperatures, from a few days to two to three weeks,” says Mora-Soto. Cool water can act as air conditioning for the kelp, regulating their environment and keeping the temperature pleasant. Wind patterns affecting ocean surface circulation and heat flows, or cold water traveling around Antarctica, could also be factors, she added.

“The heat wave story has emerged over the past decade, but the cold wave story has not been told. I think that’s quite interesting to think about in terms of kelp’s resilience,” said Kira Krumhansl, a marine ecologist at the Bedford Institute of Oceanography who was not involved in the new study. “It’s nice to understand that there’s another climate signal here, where the climate isn’t warming as quickly and the waters are closer to the temperatures the kelp can tolerate, which seems to lead to their resilience and perseverance.”

Keep Kelp happy

The prospects for these kelp forests may remain rosy, at least for the foreseeable future. Current climate and ocean models predict that the Southern Ocean, the waters in which these thriving kelp forests live, will prevent drastic warming. But as glacial melt increases, that freshwater can bring sunlight-blocking sediment, different sets of nutrients, and even too-cold temperatures.

“If there’s ice in the system, that can be very stressful for kelp,” Mora-Soto said. Scientists don’t yet have well-defined windows for how long different kelp species can tolerate extremely cold water.

Mora-Soto emphasized the need to protect these uniquely successful kelp forests. “In Southern Patagonia, most of the lands around the kelp forests are protected, but not necessarily the waters,” she said. “And in Chile’s northern regions, kelp forests are harvested for the alginate industry, creating underwater deserts in environmentally friendly conditions. I hope environmentalists, NGOs, local communities and the current government can help make kelp protection a real one.”

“I think we’re on the cusp of learning more and more about the value kelp forests have to humans,” Krumhansl says. “They’re often undervalued, but they’re amazing ecosystems, just wonderful to be in. And they offer a lot of benefits in focusing on and protecting.”

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