On a recent plunge into Monterey Bay, Dr. Anita Giraldo Ospina noticed the water was oddly warm.
“It definitely feels comfortable, let’s put it that way,” said Giraldo Ospina, principal investigator of coastal ecosystems at the Monterey Bay Aquarium.
She’s part of ongoing research projects into how kelp species are repopulating the area. She collects kelp spores and tiny baby urchin from glass slides and rectangular broom heads anchored to the seafloor and stores them in plastic bags.
“It looks pretty green down there,” Giraldo Ospina said. “We try to keep all the water in the bag because that’s where larvae settle into the brushes and that might be what’s floating in the water.”
Baby kelp need cold, nutrient rich water to mature into tall, strong adult stipes. Giraldo Ospina worries that a massive, ongoing marine heat wave, which has already raised coastal waters by 3 to 4 degrees Fahrenheit, could disrupt efforts to regrow kelp forests vital to the Monterey Bay ecosystem, depending on how warm it becomes.
“We have seen kelp recovering, and we don’t know if that trend is going to continue, if we continue to have these warm waters,” Giraldo Ospina said.
It’s the seventh marine heat wave in seven years and could be amplified by a developing super El Niño, which has the potential to raise sea surface temperatures even higher. This combined influence could disrupt ecosystems, harm or kill local marine life and attract other species north.
“With El Niño, the fear is that the kelp that persisted [past the marine heat wave] may now decline, and recovering kelp may not get a chance to get back to what they were before,” Giraldo Ospina said.
Even a few degrees of warming can set an ecosystem out of whack and lead to the die-off of almost entire populations. As of May 20, the International Bird Rescue in Fairfield has treated 288 starving birds, including brown pelicans, cormorants and common murres.
“They are the same birds people are reporting finding dead on beaches, especially in Southern California, but now in Northern California as well,” said JD Bergeron, the group’s CEO.
Bergeron said one theory is that small schooling fish — favorite food for shore birds — are seeking colder water deeper in the ocean, beyond the birds’ reach. So they do not have enough food to eat.
“We have had very regular concerns with brown pelican starvation events, but this one does feel a little bit different,” Bergeron said. “We’re seeing a lot more dead birds than living ones being found.”
A marine heat wave off the coast of California forms when southerly winds from a semi-permanent area of high pressure weaken between Hawaii and the state.
The winds normally help cool the top layer of the ocean through evaporation and by mixing it with deep, cold water. Without the wind, this thin top layer warms.
The current ocean warming began last May near Eastern Asia and spread across the Pacific.
Some waters have had little break since mid-2025, with more than 200 days of elevated temperatures, according to researchers with Climate Central, who said human-caused climate change has significantly intensified the marine heat wave.
Up to 45% of the ocean impacted “is experiencing conditions that are at least six times more likely due to human-caused warming,” Climate Central said.
Without climate change, they wrote, the heat wave’s footprint would be 36% smaller.
An El Niño event can weaken winds and slow the upwelling of cold, nutrient-rich water, which could further intensify the marine heat wave. Without that strong mixing, warm water lingers at the surface, causing temperatures to spike.
“All the ingredients are there for a strong El Niño,” said Tom Di Liberto, media director and climate scientist with Climate Central. “If you’re making cookies, you’ve already mixed the dough, but haven’t baked them yet. We still have to wait to see if, in the summer months, these cookies get put in the oven to see if we have that strong El Niño form.”
Daniel Swain, a climate scientist with UC Agriculture and Natural Resources, said in a recent live-streamed office hours series that while El Niño is not directly related to the marine heat wave, “later this year, it’s actually quite likely that El Niño will reinforce this tropical warming.”
Because El Niño refers to the “sloshing of water from the tropics to the Eastern Pacific it can and does impact sea surface temperatures along the California coast,” said Alexander Gershunov, a research meteorologist at the Scripps Institute of Oceanography at UC San Diego.
“It can even result in very different species of fish appearing off the coast here as the upwelling shuts down,” Gershunov said.
If waters get even warmer, jellyfish, crabs, dolphins, sea turtles and other species could move into colder habitats, said Dr. April Ridlon, director of science for the U.S. Ocean Conservation at the Monterey Bay Aquarium.
“The more we change the ecosystems, the more possible it is for those warm water species not just to arrive every once in a while and be a novelty and a news article, but for the fundamental composition of the ecosystems to change over time because the warm waters just don’t stop,” Ridlon said.
Ridlon said the current marine heat wave reminds her of “The Blob,” a warming event that ended about a decade ago. It decimated about 60% of kelp along the Central Coast and nearly all of the kelp off the coast of Northern California.
Warming water accelerates the metabolism of purple urchins, causing the marine animal to voraciously devour kelp forests. Even after the kelp disappears, they can survive as “zombie urchins” in a low-energy state, said Daniel Okamoto, a professor in the Department of Integrative Biology at UC Berkeley.
“They can sit there for decades and just hang out,” Okamoto said. “Anytime the kelp tries to come back, they have the potential to graze it down.”
He’s also worried about red abalone, whose populations have declined by up to 95% off California’s North Coast. Unlike urchins, they can’t survive in starvation mode.
“They’re in a really, really fragile state,” Okamoto said. “The impending marine heat wave may cause some additional harm on top of what’s already been done.”
Sunflower sea stars nearly vanished off the California coast when an ocean warming event accelerated the effects of a marine plant disease.
“I don’t even think anybody really appreciated their importance until they were gone,” Okamoto said. It was the “equivalent of their global pandemic that wiped out most of those organisms.”
To learn more about how we use your information, please read our privacy policy.