California, April 2025: A disturbing wave of aggression by sea lions along California’s coast has left beachgoers alarmed. The animals, usually playful and calm, have begun attacking humans a behaviour scientists describe as both unprecedented and “demonic”.
At the heart of this troubling transformation is a toxic algal bloom off the southern Californian coast. The algae, Pseudo-nitzschia, produces domoic acid, a potent neurotoxin that has infiltrated the marine food chain. Small fish consume the algae, and larger predators like sea lions feed on them, unknowingly ingesting the toxin.
The result has been devastating: hundreds of sea lions lying sick along the coast, suffering from muscle spasms, confusion, and extreme aggression. Some have bitten surfers and beach visitors. While no fatalities have been reported, experts warn the situation could escalate given the animals’ size and strength adult males can weigh up to 300 kilograms.
Kathi Lefebvre, a NOAA research biologist, told National Geographic that domoic acid overstimulates sea lions’ nervous systems, causing them unbearable stress and violent outbursts. She has been studying the effects of domoic acid in marine mammals for over two decades.
What’s even more concerning is that this neurotoxin can affect humans too. If consumed in large quantities through contaminated seafood, domoic acid can lead to severe health issues including seizures and, in extreme cases, death.
But what caused this sudden bloom of toxic algae?
According to marine researchers, nutrient accumulation in ocean waters caused by both natural and human-induced factors leads to algal blooms. One major driver is upwelling, a phenomenon where nutrient-rich deep waters rise to the surface, especially during strong wind events. These winds, intensified by climate change, are now more frequent and severe.
Another contributor is pollution. Agricultural and industrial runoff often carries nitrogen-rich waste into the ocean, feeding toxic algae. Adding to this year’s bloom, experts suspect runoff from recent wildfires in Los Angeles further disrupted the marine ecosystem, triggering this crisis.
NOAA noted in a recent report that this is the fourth consecutive year Southern California has seen harmful algal blooms affecting marine life. While many sick dolphins are beyond help, some sea lions are being rescued and treated in authorized rehab centers.
As climate change continues to warm oceans and increase environmental instability, marine scientists warn that such toxic events may become more frequent and harder to control.
For now, Californians are being urged to stay cautious near coastal areas and avoid close encounters with stranded sea lions. Behind their aggression lies not malice, but a deeply distressing and toxic transformation driven by a warming planet.