Marine Die-Offs Signal a Climate Emergency
By Dom Altomari, October 5, 2025
Mass die-offs of sea life are sweeping coastlines as warming seas and pollution trigger toxic blooms and heatwaves. Scientists warn these cascading losses are a glimpse of what’s to come without urgent climate action.
Photo Source: CBC News
This summer, shorelines from California to Australia experienced alarming mass die-offs of marine life; a clear warning sign of warming, polluted oceans. In Southern California (SoCal), an unusually early and intense harmful algal bloom (red tide) “poisoned scores” of sea lions and common dolphins with domoic acid, leading to hundreds of strandings and many deaths. At the same time, parts of Western Australia have been experiencing “ongoing marine heatwave” conditions that warmed coastal waters to 4-5 °C above normal temperatures. In Western Australia’s Pilbara, over 30,000 fish washed up dead in January on Gnoorea Beach near Karratha. The South Australian state Premier Peter Malinauskas announced a “natural disaster” was unfolding due to a massive bloom of the marine phytoplankton Karenia mikimotoi. The bloom has spanned over 4,500 square kilometers of reef and coast to date, and has killed an estimated 34,000 animals (from fish and cuttlefish to leafy sea dragons), proving “catastrophic for marine animals.” Scientists link these events to climate-driven warming and nutrient runoff and warn that these phenomena are likely harbingers of more frequent disasters unless we change course.
California sea lion stricken by the neurotoxin domoic acid from a harmful algal bloom in Santa Barbara County, California. [Photo Source: Channel Islands Marine & Wildlife Institute]
Southern California: Toxic Algae Strikes Again
Researchers warn that the 2024-25 bloom off the Californian coast is “the deadliest and largest toxic algal bloom recorded.” Nutrient-rich upwelling fueled explosive growth of the algae Pseudo-nitzschia, which produces the neurotoxin domoic acid. As the National Oceanic and Atmospheric Association (NOAA) reports, this bloom has “poisoned scores of California sea lions and common dolphins,” with stranding networks logging over 100 rescue calls per day. By spring of 2025, more than 100 dolphins (ten times the typical toll) had been sickened or killed. Rescuers note that “many of these animals are really suffering” and are forced to triage patients and even euthanize some to prevent worse pain. Remarkably, NOAA says this is now the fourth straight year of major blooms impacting SoCal’s marine life. Experts attribute the severity of these events to earlier-than-usual bloom conditions: after record rainfall and wildfires across California, runoff carried extra nutrients offshore, and a February upwelling pulse jump-started algal growth early. Glenn Gray of the Pacific Marine Mammal Center described the extent of the catastrophe: “The number of dead dolphins we’ve had this year is just off the charts. We’re all dealing with numbers within a two-month period of time that would normally represent the number of responses we would make in a year. It’s been the worst that’s on record in terms of how it’s affecting the animals and the different species of animals.”
Australia’s Disaster Beneath the Waves
At the same time, half a world away, Australia’s coastal communities have seen their own fair share of eco-catastrophes. In January of 2025, the Department of Primary Industries reported that approximately 30,000 fish were found dead along a 9-kilometer stretch near Gnoorea Point (Pilbara coast). Water temperatures were abnormally high, ranging from ~31 °C, 2-5 °C above normal, placing a marine heatwave warning in full force. Scientists say prolonged thermal stress from this climate-driven ocean warming most likely caused the die-off. This event is reminiscent of the catastrophic 2010-2011 marine heatwave, which caused similar temperature spikes that devastated over 1,300 square kilometers of Shark Bay seagrass, crippling abalone and scallop fisheries. Department of Primary Industries and Regional Development (DPIRD) spokesman Nathan Harrison said the effects of the 2010-2011 heatwave were still being felt in commercial fisheries.
Meanwhile, in South Australia, an unprecedented Karenia bloom (likely fueled by a climate-driven marine heatwave plus nutrient runoff from inland floods) has swept from Spencer Gulf into Adelaide’s metro waters. The bloom covers over 4,500 square kilometers, spewing foam on beaches and causing irritation for swimmers since March 2025. Local councils report collecting between 40 and 200 kilograms of marine carcasses per day from beaches as fish, sharks, rays, sea dragons, and birds continue to pile up. Citizen scientists have logged about 34,000 dead animals across ~480 species on iNaturalist.Experts say the bloom shows no sign of stopping, pointing out that warm winters can no longer "stop" these events as numerous compounding factors from warming to pollution damage these systems beyond immediate repair. The crisis is so severe that even the Red Cross is calling it a “slow-onset disaster” and urges a “fast and just recovery” to address both the environmental and human trauma.
Algae concentrations are shown in this satellite photo from September 7. The areas in red mark higher concentrations of algae. The green zones show the South Australian land mass. The thick red areas are concentrated around Adelaide and the St Vincent Gulf. [Photo Source: Supplied]
The Frontline Communities
These marine disasters are not just ecological tragedies, they also devastate communities and frontline groups whose lives and cultures depend on healthy oceans. Coastal fishers and Indigenous communities face repeated losses of food, income, and heritage as these disasters become more and more common. Pilbara Malgana custodian Sean McNeair, whose family re-plants seagrass, warned that “if the country’s not being looked after and the country's sick, we’re also sick.” Residents in Adelaide have reported eco-anxiety as they watch beloved wildlife wash ashore. Conservationists note the cruel irony: the massive fish kill in West Australia occurred just down-current from one of Australia’s largest gas mega projects known as the Burrup Hub built by Woodside Energy, further highlighting the link between local pollution and global warming. Once again, low-income and indigenous communities are forced to bear the brunt of climate-driven disasters, while big polluters carry on as usual. Climate campaigners like Paul Gamblin bluntly warn that, “What’s happening in our blue backyard this summer is something we really need to heed…if we don’t, that’s on us.” Environmental justice groups have echoed these sentiments, demanding accountability from the fossil fuel industry about the mass die-offs plaguing their communities. Every new fossil fuel project approved today will fuel the future mass die-offs of tomorrow.
How Can We Prevent More Die-Offs?
Preventing future marine die-offs will require collective, long-term action on climate, pollution, and community resilience. Key steps include:
Cut greenhouse gas emissions: Nearly 90 percent of marine heatwaves are now driven by human-caused warming. The most urgent remedy is to rapidly phase down fossil fuels and scale up renewable energy. Citizens can press their governments for stronger climate policies by opposing new oil and gas projects and demanding swift investments in clean energy. Individual choices- such as using public transit, conserving energy, eating a plant-rich diet- also help cut emissions.
Control coastal pollution: Runoff of fertilizers and wildfire ash fuels harmful algal blooms. Stricter regulations on agricultural and urban runoff, combined with better wildfire debris management, would significantly hold off toxic tides. Implementing coastal sensors and community monitoring can provide early warning of blooms. For example, NOAA’s Harmful Algal Bloom Monitoring System helps local authorities decide to close beaches to protect public health.
Support wildlife rescue and restoration: Local rescue centers and volunteers are on the frontlines of these disasters (and most others) doing heroic behind-the-scenes work by treating poisoned sea lions, cleaning up beaches and surveying species. Expanding habitat restoration projects such as replanting seagrass and kelp will bolster ecosystems’ resilience to heat stress and protect vulnerable communities from contamination.
Center community recovery: Marine die-offs should be treated as what they are: public health emergencies. Governments must provide aid to affected communities, including flood relief funds, support crews, healthcare for stranded workers, and support for local industries and Indigenous stewards. As the Australian Red Cross advises, responses should aim for a “fast and just recovery” that addresses both environmental damage and community trauma. In policy terms.
These unprecedented die-offs are devastating and undeniable proof that without urgent changes in habits and policies, mass marine mortalities will become routine events.
Take Action
Public advocacy has proven time and time again to be our most critical line of defense. Here are ways that you can help:
Sign on to Greenpeace’s petition calling on the Australian Federal Government to “protect the Great Barrier Reef from the impacts of climate change by replacing all coal-burning power stations with clean and safe renewable energy by 2030 and committing to net-zero by 2035.”
Email MP Matt Smith: “Commit to protecting the Reef.”
Add your name to this petition to Environment Minister Murray Watt by Save Our Marine Life.
Sign the Petition: Government must take action on the SA Algal Bloom.
Sign change.org’s petition to “Address Algae Bloom Crisis in South Australia.”
Volunteer with or donate to local marine wildlife rescue organizations and ecological restoration projects.
Add your signature to this change.org’s petition to “Call for Transparency.”
Forward the Australian Conservation Foundation’s pre-filled letter to the PM and key ministers demanding marine protections to prevent further die-offs.
Sign the Greenpeace petition with over 50,000 signatures to stop Woodside Energy’s detrimental coastal gas projects in West Australia.
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