As British Columbia’s summer folds itself into fall, the murk of its inlets turns to glass. Shielded by granite, this salt water half an hour from Vancouver’s skyscrapers is where, every October, the jellyfish bloom. Tiny fireworks explode around their hair-like tentacles, creating a vortex under their bells that causes surrounding bioluminescent plankton to glow.

The photographer and I dive into water thick with mostly Aurelia aurita, or moon jellyfish, whose mild stings we hardly feel. We’re more wary of the occasional fried egg (Phacellophora camtschatica) and lion’s mane (Cyanea capillata) jellyfish that pulse past. Each year, the jellies return to Metro Vancouver with the currents, and remain in səl̓ilw̓ət (pronounced sah-LALE-wot) — the Hun’qumyi’num name for Burrard Inlet and Indian Arm — finding shelter in the evergreen glacial fiords.

The floating sheet-ghosts that photographers capture in səl̓ilw̓ət’s midwaters are the short-lived medusa morph. Like all jellyfish, they eat throughout their life cycle and spend most of their lives out of human sight, rooted to rocks and other structures as juvenile polyps. Docks that zipper up səl̓ilw̓ət’s green and blue shoreline — from Port Moody’s mansion-lined shallows to the jetties of Say Nuth Khaw Yum Provincial Park — offer optimal nurseries.

But in 2022, a much larger bloom seemed to appear. That year, British Columbia experienced record-breaking heatwaves that dried upstream creeks used by migrating salmon to return to their spawning grounds. Locals say səl̓ilw̓ət’s deep arms, shared by jellies and fish alike, remained full later during these runs. That meant both the moon jellies and the larval salmon were competing for the same precious food source: plankton. “Everything depends on zooplankton,” says jellyfish researcher Jessica Schaub, whose drone research was the first to track Aurelia aurita distribution farther north in Pruth Bay, B.C.

Though drones reveal the galaxy-like dispersion of jellies in shallow waters, they can’t accurately measure biomass or how bloom sizes vary each year. Ballooning jellyfish numbers could exacerbate challenges for already-threatened populations of wild salmon.

Musqueam Nation fisheries officer Willard Sparrow fears for the keystone fish that B.C.’s First Nations depend upon. His band’s territory is home to one of Vancouver’s last wild salmon streams. “Over the past 10 years, we’ve noticed more jellyfish blooms,” he says of their local waters, concerned about compounding effects like lowering dissolved oxygen levels. Unlike jellies, the five species of Pacific salmon — coho, chinook, sockeye, pink and chum — are Canadian homebodies, needing cool, flowing water in more discerning conditions than their gelatinous inlet-mates.

Rising sea temperatures could play a role, too. “When you have an extended summer period, then you would have more productive (bloom) conditions later into the year,” says Brian Hunt, an oceanography professor at the University of British Columbia. Should the short window for jelly breeding widen, it may result in more juveniles in any given year, leading to larger blooms. In that 2022 bumper-crop year, Port Moody, one of səl̓ilw̓ət’s shoreline cities, was still sweating through highs of up to 28 C during mid-October.

Since time out of mind, səl̓ilw̓ət has been the traditional territory of the “People of the Inlet,” the Tsleil-Waututh (səlilwətaɬ) Nation — the band is named after this body of water, revered as their first grandmother. The nation continues to steward these waters, for example by restoring a groundwater channel (that was previously clogged during a logging road landslide) in time for the biennial pink salmon run. Living in “seasonal rounds,” the Tsleil-Wautt people were once guided by the seasons in a complex, cultural cycle of food gathering and spiritual activities.

“Wet, dry and hot: they’re the only seasons we see now,” sighs Sparrow, whose nation’s territories overlap with Tsleil-Waututh lands and waters to the south.

Of around 110 jellyfish species in Canada, 75 can be found off the coast of British Columbia. But between Khenipsen octopus legends, Tsleil-Waututh lore on inlet serpents and Tsawwassen sturgeon-harvesting stories, I struggle to find oral history about jellyfish. That’s likely because “we don’t eat jellyfish,” Sparrow says.

The fisheries officer is concerned that the beauty of the blooms masks their impact. “They are an indicator of the conditions of the water — acidification, low oxygen, warmer water — and that creates a cycle of bigger, more frequent blooms. This compounds the issue of human impact and climate change.”

For now, səl̓ilw̓ət’s spawning secrets are obscured by a need to collect more jellyfish data, according to scientists like Schaub — especially because, in other places, blooms of jellyfish tend to show up when fisheries collapse. In Namibia, for example, when commercial fish stocks collapsed, jellyfish populations exploded with the greater availability of food. Off coastal Ireland, the stinging tentacles of two types of sea jellies, including Aurelia, caused severe gill disorders that killed thousands of farmed salmon. Around the world, fishery interactions with jellyfish have cost the industry millions.

Yet jellyfish bells may not necessarily signal alarm. They’re also an important functioning part of the ecosystem, say Schaub and Hunt. Juvenile fish and crustaceans shelter in them, and when jellyfish die and sink to the sea floor, they provide nutrients that feed the food web and even sequester carbon.

“We need systematic monitoring of jellyfish to find out if changes are actually occurring. Otherwise, we can only speculate,” says Hunt, who is now overseeing research in səl̓ilw̓ət. Schaub advocates for regular, dedicated sea jelly measuring — “and we don’t have that right now.”

For creatures so translucent we can see their organs, there’s still a lot unclear about the jellies of the inlet. Their soft bodies leave no clues in the bone and shell middens of ancestors past. Instead, we surface from səl̓ilw̓ət with just the bubbles from our breath — the bioluminescence illuminating the surrounding moon jellyfish like windows into a nebulous future.