Reporters have spent a lot of time, and ink, asking humans how they feel about this year’s El Niño. The much-hyped weather event has sloshed its way, in the form of an enormous pool of warm water, all the way across the Pacific. A persistent preexisting marine heat wave off the California coast and climate change are probably supercharging its impacts.

For many people, the answer may be alarmed. According to homeowners, El Niño means it’s time to clean your gutters and storm drains. According to firemen, it means more fires. According to anyone living near the ocean, it means battening down the coastal hatches.

But this is Bay Nature, so we asked around with the Bay Area’s nature—or at least the scientists studying it—what El Niño means, according to them. From the oak trees in the East Bay hills to the kelp forests of the coast to the anchovies in the seas to murres diving off the far-out Farallones, every species has a different story to tell.

According to the blue oak tree, El Niño can be a time to stock up for the future.

One year is a blink among the four centuries the endemic, sweeping tree can live. But it’s a year each tree records. A blue oak (Quercus douglasii) owes much of its longevity to its ability to endure months—or years—without rainfall. On the flip side, when El Niño sends Pacific Ocean temperatures skyrocketing, and makes deluges more likely over California, blue oaks soak it all in. “It is the most rainfall-sensitive species on Earth,” says David Stahle, a dendrochronologist—a scientist who studies tree rings—at the University of Arkansas.

A blue oak at Round Valley Regional Preserve, near Antioch. Dan Griffin, University of Minnesota, via David Stahle

Stahle has spent decades visiting, and marvelling at, blue oaks in the East Bay hills. Their roots stretch down to 70 feet or more to tap groundwater far beneath the surface. In heavy rains, the matted network of fine surface roots, which extend far beyond the tree’s canopy, absorb all surface water readily, trapping nutrients and creating small, fertile worlds around them.

In the tree cores Stahle drills from their trunks—which he extracts with permits, and which he promises do not harm but simply “insult” the trees—he finds careful records of California’s El Niños in each band of growth. Most El Niños are defined by thick rings, recording the fresh growth spurred by rain. In drought years, bands stay thin as blue oaks conserve their energy.

True-color thin section from a blue oak in Mount Diablo State Park, with the annual rings highlighted. Dan Griffin, University of Minnesota, via David Stahle

A photomicrograph of a blue oak specimen, stained to enhance the woody structures. Variation in the annual ring width can be used as a proxy for rainfall; 1583 was a wet year, while 1585 was a dry one. Dan Griffin, University of Minnesota, via David Stahle

Matched to known El Niño years, oak rings confirm what the National Weather Service keeps telling us: El Niño in California does not guarantee rain. About half of past El Niños, Stahle has found, did not bring extreme rainfall in the Bay Area, according to its blue oaks. Some years may even be drier than average. Then, blue oaks may drop their leaves and go dormant, betting on wetter years to come.

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Blue oak distribution in California. Griffin and Critchfield (1972), via David Stahle

There is such a thing as too much rain, though. (Or overwatering: “You can kill them with love,” says Stahle.) And as scientists predict an extremely wet El Niño, forest caretakers are beginning to worry that months of persistent flooding could rot oak roots. Chris Lee, a forest pathologist with Cal Fire, notes that water can also revive microorganisms like the bacterium that causes sudden oak death, which has killed 50 million trees along the West Coast since its 1995 discovery. No blue oak deaths have yet been recorded from the bacterium, but Lee expects to see swathes of brown, dead tanoaks within the next few years, as the microorganism blooms and begins to burrow into tree trunks this winter. Other microorganisms, including newer invasives, are likely to get a watery boost too.

If blue oaks thicken with the record of this exceptional year, it may be in a lonelier, sparser landscape, with fewer tanoaks around. But after centuries, these trees have seen everything move in cycles. “They definitely survive,” says Stahle.

According to bull kelp, El Niño makes a hard life harder.

El Niño reaches the Bay Area’s kelp in the fall with a thousand-mile wide wave. Created as the warm pool of El Niño waters bounces north from the Peruvian coast, this Kelvin wave, as it’s known, can raise sea levels by a foot. It upends the kelp world. Normally, the California coast is chilled and nourished all summer by cold, nutrient-filled water welling up from the deep. But the immigrant wave can push down the fertile bounty at a key moment in kelp life cycles.

Bull kelp forest. Chad King / MBNMS

By the fall, kelp’s waving, shimmering blades have just thickened with mats of sori, a specialized kind of reproductive tissue. Nestled in the sori are masses of microscopic spores, each with two microscopic tails and half of a future kelp’s genes. The spores release when the water is warmish, not too choppy, and full of nutrients, says Rietta Hohman, who has spent eight years restoring kelp at the Cordell Bank and Greater Farallones National Marine Sanctuaries.

But Hohman thinks kelp spores have more trouble forming gametophytes in El Niño’s hotter waters. As a result, fewer sperm and eggs are released, and kelp sex plummets. The few baby kelp that do form spend the winter growing knotted, microscopic holdfasts to lash themselves to the seafloor. El Niño-exacerbated storms likely uproot these fragile anchors, cutting down the kelp numbers that make it to spring even more.

Baby bull kelp, under pink grow lights in the lab. Maria Velazquez, Greater Farallones Association

Historically, this damage didn’t matter, because one bull kelp can produce over three trillion spores. When conditions improve, satellite records have shown, populations bounce back. “We just haven’t seen those conditions in over a decade,” says Hohman. Kelp has yet to recover from its crash during the 2014–2016 El Niño. Along the Northern California coastline, a new ecosystem dynamic has taken over: one where kelp-gobbling urchins thrived since populations of their predators the sunflower sea stars crashed. Underwater forests have transformed into spiky purple barrens. Hohman and her colleagues have spent years trying to undo, and understand, that damage.

The team has learned about what they can control. They can kill urchins, by deploying teams of weaponized divers—as long as the water isn’t too rough, another El Niño concern. They can grow kelp in labs. They can come up with new ways to plant spores in the ocean. “But we can’t really manage ocean temperatures and these bigger processes and cycles,” Hohman says. That’s something they hope bull kelp can do, if they survive—they’re very good at sucking CO₂ out of the atmosphere.

According to scientists, El Niño is bad news for the northern anchovy. (But last time, the northern anchovy didn’t get that memo.)

Anchovies aren’t approaching life with a plan. Their odd-looking babies are born still attached to their yolk sacs, which sustain them for about three days. After that, the larvae drift with the current, feebly beating their caudal fins and eating whatever fits in their mouth. To survive, “they just have to get lucky,” says Andrew Thompson, a fish biologist with the National Oceanic and Atmospheric Administration’s Southwest Fisheries Science Center.

Northern anchovy (Engraulis mordax). Steve Lonhart / NOAA MBNMS

El Niño sounds like bad news for these fish. When warm waters trap oxygen in deep water, and warm-water-loving jellies dominate instead of nutritious crustaceans, baby anchovies starve. In 2003, Francisco Chavez, a research biologist at the Monterey Bay Aquarium Research Institute (MBARI), modeled anchovy populations over a half-century and seemed to discover biological law: anchovies didn’t like it hot.

Northern anchovies in a tank show off their dramatic overbites. They’re filter feeders. Steve Lonhart / NOAA MBNMS

But after the 2014–2016 Blob, anchovies reached record highs in their population off the Bay Area, reshaping our marine ecosystems in turn—driving whales to Pacifica, and sending salmon spinning (because anchovy overindulgence actually degrades key vitamins in salmon bodies). Thompson thinks anchovies thrived because cold, nutrient-rich waters persisted in smaller pockets close to the coast during the last El Niño, rather than disappearing altogether—a phenomenon called habitat compression. Adult anchovies spent their time in the remaining upwelling, because that’s where the food was. Females laid massive clouds of eggs there, and so most larvae got to hatch into one of the El Niño ocean’s few remaining food bonanzas. “It’s not really survival of the fittest,” says Thompson. “It’s more just survival of strength in numbers.” Another factor: sardine populations, which live further out from shore, crashed, meaning anchovies had less competition. And as anchovy fisheries have declined over the last half-century, fewer fish were scooped up for pizzas.

It’s unclear if anchovies can expect to thrive again, as they enter this El Niño on record—possibly unsustainable—highs. Coastal upwelling has remained strong so far in California. It may depend on if upwelling pockets emerge again, or perhaps another oceanographic surprise. Chavez, for one, is burned on predicting anchovy numbers. “If you make a law of something, you know it’s going to get broken,” Chavez says.

One thing is certain: what happens to anchovies ripples far beyond them into the marine food web.

According to common murres, El Niños make their leap of faith a lot dicier.

In October, a common murre chick is two months past the biggest jump of its life—toppling off Farallones cliffs hundreds of feet into the ocean, wings barely formed, toward its waiting parent. “It bounces down off the rocks and ends up in the water and bobs right back up like a cork and then swims off,” says Pete Warzybok, a bird researcher and murre lover with Point Blue Ocean Science who has spent decades at the Farallon loomeries (that’s the scientific term for colonies of murres).

Our local common murres probably would not, if asked, have nice things to say about El Niño. Brooke Johnson via iNaturalist, CC-BY

Accompanied and tutored by its dad, the murre chick spends autumn swimming in search of food—ideally anchovies or other forage fish. Both parent and child need a lot of it, and fast. The parent because it just shed all its flight feathers, and needs the energy to grow the feathers back. The chick because it has a whole lot of growing to do.

But El Niño’s warm waters can make finding food difficult, in part because baby murres can’t—and shouldn’t—eat everything. A murre chick can’t swallow a full-sized adult anchovy, for example, no matter how lovingly it’s offered by dad. And jellies are as bad for a baby murre as they are for a baby anchovy: gelatinous animals can fill a tummy, but are the nutritional equivalent of junk food.

After the fall pulse of upwelling subsides, El Niño begins to exact its full toll. After October, each chick is left to its own devices. The adult murre begins thinking about the next breeding season. It will return to its home loomery, reunite with its mate, and defend the scrap of rock where the couple will bring their next egg into the world.

During most El Niños, those return visits can become more infrequent, because each murre must travel farther to find food in the warm, unproductive seas. Stormy waters can make a murre desperate: shoals of fish are harder to pick out amid rough, chaotic waves, which can overwhelm a young murre foraging alone for the first time.

Regardless of breeding success, common murres are committed to the ritual of nesting, Pete Warzybok says. “They’ll find a rock, and they’ll find a piece of Farallon weed, and they’ll start sitting on it like it’s their egg… They do what they do, and not a lot changes.” Brooke Johnson via iNaturalist, CC-BY

Several years of anchovy population booms, and a strong upwelling around the Farallones, have provided a “buffer” for murre survival, says Warzybok. But maybe not enough. Marine ecologist Tammy Russell has spent months finding emaciated murres washed up on San Diego beaches, far out of their normal range. She suspects murres foraging further out at sea are starving, desperate, and confused, as the offshore marine heat wave has emptied waters of food. “It makes me sad,” says Russell, a postdoc at the Scripps Institution of Oceanography. “I wonder if they’re wondering—not to anthropomorphize—‘Where do I go? Is my mate going to be there when I show up?’” Some murres’ mates never return to the Farrallones.

In bad food years, murres can adapt, says Warzybok. This year, he saw murres wait to breed until right after the worst of the marine heat wave, and parents pushed their chicks out earlier, presumably to save their own energy. As a result, despite the warm waters and the lack of food, the Farallones loomeries had a normal breeding year. In a particularly horrible year—like the 1998 El Niño—Warzybok has seen murres skip breeding altogether, waiting for more cornucopic times to come.

According to marine scientists, all bets are off.

Francisco Chavez has spent some time clearing his gutters this fall. Beyond that, though, the MBARI scientist doesn’t know what to expect from this El Niño. “It’s a little bit of chaos, and chaos is hard to predict,” he says.

So he and other biologists across California are focused on keeping environmental monitoring consistent. That way, they can understand what El Niño changes. Point Blue Ocean Science and the National Oceanic Atmospheric Administration are launching their 22nd year of ACCESS cruises to count whales, seabirds, and marine creatures, and draw up plankton from the depths. Chavez is listening for ocean noises at the bottom of the Monterey canyon, comparing the audio volume to past years. Rietta Hohman and her team have more instruments in the water than ever before to document how kelp forests respond to El Niño waters. David Stahle is peering at the millennia recorded in his tree rings, looking to the past to help us understand the present.

Andrew Thompson, when he wakes up every morning, checks the temperature at the Scripps Pier in San Diego, and watches it continue to tick up. “I’m such a nerd,” he says. He’s counting down the days till he can get back on the water with the fisheries monitoring crew, and begin looking for anchovy again. “These are conditions we’ve never seen before,” he says. “I can’t wait to see what the biological response is going to be.”