Toxic Algal Bloom Causes Mass Cetacean Deaths

In April 2025, an outbreak of the “worst ever” harmful algal bloom off the coast of Southern California in the United States resulted in the stranding of at least four cetaceans (humpback, minke, and gray whales) due to chondrichthyan acidosis. Autopsies showed that the cetaceans had concentrations of toxins well above safe thresholds and suffered severe neurological damage. Algal blooms are triggered by warming of sea water and agricultural runoff due to climate change, releasing neurotoxins that are enriched through the food chain and threaten the cetaceans’ survival.