Northern Patagonia’s fjords are about as remote as a coastline gets. That made them a good place to test a comfortable assumption: that while kelp forests have been collapsing in California, Tasmania and elsewhere, the giant kelp of southern Chile has quietly carried on. A team led by Albert Pessarrodona of the University of Western Australia, working with Rewilding Chile and researchers in Chile, Argentina and Canada, went back to check. Their paper, published in Regional Environmental Change, is the first resurvey of these forests in more than half a century.
What makes the comparison possible is a set of dives Paul Dayton made in 1972. Dayton is a pioneer of kelp ecology, and he is a co-author on the new paper. In February 2026 the team surveyed twelve sites in Chile’s Aysén region, running from sheltered inner fjords out to the open coast. Five of those sites were ones Dayton had visited. Divers swam fixed transects, counting and measuring giant kelp holdfasts and stipes, tallying sea urchins and snails at set depths, and recording what covered the rock. They then used statistical models to line the new numbers up against the old ones.
The kelp itself is the reassuring part. The density of adult giant kelp was not significantly different from 1972, and today’s adult holdfasts were actually larger. There were fewer young recruits than Dayton recorded, but the authors think that mostly reflects timing: his surveys were in November, theirs in February. The rest of the reef tells a different story. The red sea urchin Loxechinus albus, the target of what the researchers describe as the world’s largest sea urchin fishery, has fallen by 59 to 90 percent, and the biggest individuals are now smaller. A small native urchin, Pseudechinus magellanicus, has all but vanished from the shallows; the team found it at only four sites, in very low numbers. In its place, the plumose anemone Metridium senile, which was absent in 1972 and first turned up in Chilean Patagonia in 2005, now dominates the rock at many sheltered sites, covering up to 88 percent of it. “This invasive anemone now blankets hard substrates across many locations,” Pessarrodona said. Bright green sea lettuce (Ulva) has also spread, carpeting more than 80 percent of the bottom at some sites.
It would be easy to read this as a simple story of harm, and the authors are careful not to. Their historical data were incomplete, so they had less to compare against than they would have liked. The sampling seasons didn’t match, and the study covers a limited stretch of coast. They also found no clear link between how much anemone was present and how many young kelp there were. Whether the anemone is actually harming the forest, or simply filling space, still needs to be tested with experiments. What they do describe is a forest whose structure looks intact while the community underneath it has clearly shifted. “These findings show that there are now very few places in the ocean untouched by human activity,” Pessarrodona said.
This is the first paper from Rewilding Chile’s Patagonian Megatransect, a survey running more than 1,200 kilometres from the Gulf of Corcovado to Cape Horn that will also look at how much carbon these forests store. The authors call for long-term monitoring to see whether the changes underneath start to affect the kelp itself. Co-author Mathias Hüne of Rewilding Chile goes further, arguing that marine protected areas in southern Chile are crucial if these forests are to stay one of the world’s kelp strongholds.
Further reading: Pessarrodona, A. et al., “Footprints of global change in Patagonian kelp forests after half a century,” Regional Environmental Change (2026); University of Western Australia, “Human activity threatens biodiversity in remote Patagonian kelp forests,” UWA News (2026).