California Sea Lions Have Become More Aggressive Thanks to Toxic Algae Blooms

Sea lions are a beloved fixture on California shores from San Diego to San Francisco. While the mammals usually keep to themselves, two injuries at Orange County beaches this week have left some experts questioning what's led to the seemingly sudden spike in aggression.

On June 26, a young swimmer at Salt Creek Beach alerted lifeguards that he'd been bitten while in the water. The next day, Strands Beach closed to the public after lifeguards received reports of an aggressive sea lion; that evening, another beachgoer was injured. Warning signs are now posted at both beaches letting visitors know about the potential danger.

The incidents come as California experiences a toxic algae bloom that has been killing many marine creatures, including sea lions. The algae, Pseudo-nitzschia, is consumed by fish that the sea lions eat. In doing so, they ingest a neurotoxin that the algae produces called domoic acid. The chemical essentially poisons them, causing brain damage, seizures, and death.

John Warner, the CEO of Los Angeles' Marine Mammal Care Center, believes that the sea lions suddenly becoming more aggressive is tied to their current sickness as a result of the algae bloom.

"It literally affects their brains, and the behavior of sea lions—especially when the concentrations of domoic acid are quite high—is drastically changed," Warner told NBC News. "They become symptomatic in ways that are just unpredictable in terms of their behavior, [including] aggressiveness that we don't normally see."

Due to a weakened and vulnerable state, sea lions are believed to be acting out in self-defense and fear rather than from an unexpected change in temperament. Still, it's mostly scientific conjecture at this point.

"None of this has been researched and definitively pointed to that I'm aware of," Warner said. "But putting two and two together, when you have this very large algal bloom and domoic acid event, it's pretty easy to connect the dots in a way that we're comfortable assuming that these are obviously connected incidents."

Algal blooms have sadly become more common in recent years thanks to warming oceans and changing climate. If you're planning to hit the beach along the California coast this holiday weekend, just remember to be extra cautious.