Historic Algal Bloom Decimates Marine Life Along California and Australian Coasts
A surge in harmful algal blooms is causing widespread death and distress among marine mammals and sea creatures in Southern California and South Australia, prompting urgent warnings and investigations into the role of climate change. The situation is described by experts as increasingly dire, with the scale of these events growing year after year.
California Faces Unprecedented Marine Crisis
Southern California is experiencing its fourth consecutive year of devastating algal blooms, resulting in a historically large mass stranding event. According to the Pacific Marine Mammal Center (PMMC), over 2,000 marine mammal strandings have been linked to the current bloom, surpassing all previous records. “In 2025, we’ve experienced the worst domoic acid algae bloom that we’ve ever experienced in Southern California history,” stated Alissa Deming, PMMC vice president of Conservation, Medicine and Science.
The blooms are impacting a wide range of species. Sea lions and common dolphins are particularly vulnerable, with many exhibiting neurological symptoms caused by domoic acid, a neurotoxin produced by certain algae. These symptoms include seizures and aggressive behavior, often leading to death. Tragically, the PMMC has also reported reproductive losses, with over 85 fetuses lost as a result of the bloom. Two humpback whales and a minke whale have also succumbed to the effects of the toxin. A minke whale found at Long Beach, California, earlier this year died after ingesting fish contaminated with domoic acid.
South Australia Grapples with Similar Catastrophe
The crisis is not limited to the United States. Since March, South Australia has witnessed thousands of dead sea creatures washing ashore, also attributed to a harmful algal bloom. In South Australia, the Karenia mikimotoi bloom specifically targets the gills of fish and other marine life, effectively causing them to drown. Authorities have pledged a collective $28 million to address the situation, including increased funding for testing and preventative measures.
Climate Change as a Key Driver
Experts increasingly point to a warming climate as a primary driver of these escalating algal blooms. Rising marine temperatures, combined with increased nutrient levels from cold water upwelling, create ideal conditions for algal growth. “By combining the warm sea surface temperatures with increased nutrients, that has resulted in us having a bloom event every year since 2022, with them seemingly becoming larger, longer lasting and covering a lot larger geographic region,” Dr. Deming explained.
Investigations are also underway to determine if the Los Angeles wildfires in January and subsequent runoff contributed to the bloom. The potential link highlights the complex interplay between environmental factors and the health of marine ecosystems.
Economic and Public Health Impacts
The economic consequences of these blooms are substantial. A 2024 study estimated losses to tourism-related businesses during the 2018 Florida red tide bloom at $US2.7 billion. The US National Office for Harmful Algal Blooms conservatively estimates the annual cost of harmful algal blooms in the US at $50 million, though experts believe the true figure is likely much higher.
Authorities are prioritizing the safety of both marine life and the public. The PMMC hospital is currently at capacity, and staff and volunteers are facing immense physical and emotional strain. The public is strongly advised not to approach stranded sea lions, as they may be poisoned and potentially aggressive.
Global Trend and the Need for Action
Harmful algal blooms are becoming increasingly frequent and severe worldwide. In 2016, an algae surge killed an estimated 40,000 tonnes of salmon in Chile, while hundreds of elephant deaths in Botswana in 2020 were linked to cyanobacteria. Professor Gretta Pecl from the University of Tasmania’s Institute for Marine and Antarctic Studies warns that without significant action to reduce climate emissions, these events will become even more common. “If there isn’t something done to mitigate, to reduce climate emissions, warming will continue and these kinds of events will be more and more likely,” she said.
US research biologist Kathi Lefebvre, with NOAA Fisheries, echoed this sentiment, noting that blooms are now occurring in areas previously unaffected. “We’re basically seeing that the warming climate is changing the frequency and length and locations and toxicity of harmful algal blooms,” she stated. “It is turning out to be a major impact of climate change.”
Lefebvre emphasized the need for increased monitoring and testing to protect human health and ensure the safety of the seafood supply. “What’s going to happen if these blooms are going to be continuing is that there’s going to need to be ways to test for toxins … to protect human health,” she said. “The more information we have, the better decisions we can make.” While current monitoring systems are in place, experts agree that improvements are needed globally to prevent the conditions that fuel these devastating blooms.
