{"id":2191774,"date":"2026-07-16T06:00:32","date_gmt":"2026-07-16T05:00:32","guid":{"rendered":"https:\/\/focusingonwildlife.com\/news\/?p=2191774"},"modified":"2026-07-15T08:09:06","modified_gmt":"2026-07-15T07:09:06","slug":"marine-animals-were-mysteriously-dropping-dead-around-1-million-were-wiped-out-scientists-now-know-the-reason-why-and-its-terrifying","status":"publish","type":"post","link":"https:\/\/focusingonwildlife.com\/news\/marine-animals-were-mysteriously-dropping-dead-around-1-million-were-wiped-out-scientists-now-know-the-reason-why-and-its-terrifying\/","title":{"rendered":"“Marine animals were mysteriously dropping dead: around 1 million were wiped out.” Scientists now know the reason why \u2013 and it’s terrifying"},"content":{"rendered":"

In 2025, trouble was brewing in a 20,000\u2009km2\u00a0<\/sup>area off the coast of South Australia. For more than a year, marine animals were mysteriously dropping dead: around one million animals were wiped out and some humans even got sick.<\/p>\n

Now, scientists have confirmed that the culprit behind these mass marine animal deaths is a species of microalgae called\u00a0Karenia cristata.\u00a0<\/em>The algal bloom produced several powerful toxins, which the researchers say result in stronger toxic effects than any species they have studied before.<\/p>\n

\u201cThis can partly explain the scale of the impacts witnessed in this event, which have included the mass mortality of marine invertebrates, fish, mammals and birds, over many months,\u201d says professor\u00a0Shauna Murray, a marine biologist at the University of Technology Sydney.<\/p>\n

Algae\u00a0are simple plant-like organisms that create energy from sunlight through photosynthesis. Single-celled microalgae are so small that they\u2019re invisible to the naked eye.<\/p>\n

These algae might not look as vibrant as rainbow-coloured\u00a0coral reefs\u00a0but they are incredibly important in keeping the ocean healthy: they produce oxygen, take in carbon dioxide and provide habitats and food for lots of different marine creatures.<\/p>\n

But, as with anything, too much isn\u2019t always a good thing. When\u00a0algae blooms\u00a0get out of control, things can turn nasty. One of many problems caused by harmful algal blooms (often shortened to HABs) is that some species of algae can produce dangerous toxins that kill animals and can even affect humans through the water or eating contaminated seafood.<\/p>\n

Murray and colleagues conducted lab-based experiments on\u00a0Karenia cristata\u00a0<\/em>to better understand how dangerous its toxins were. \u201cKarenia cristata<\/em>\u00a0in the laboratory was highly toxic in very low cell concentrations,\u201d she says. \u201cWe found that\u00a0Karenia cristata<\/em>\u00a0is an order of magnitude more toxic than the next most toxic microalgae that has been studied to date.\u201d<\/p>\n

Their findings are published in\u00a0the scientific journal\u00a0Nature Ecology & Evolution<\/em>.<\/p>\n

Worryingly, the scientists showed that the species behind the South Australian bloom (Karenia cristata<\/em>) \u201cproduces substantial amounts\u201d of brevetoxins (BTXs). These potent neurotoxins are commonly associated with deadly \u2018red tides\u2019(produced by another type of algae called\u00a0Karenia brevis<\/em>) and can cause devastating mass strandings of\u00a0whales, dolphins,\u00a0manatees,\u00a0sea lions\u00a0and\u00a0turtles\u00a0among other animals.<\/p>\n

\u201cBefore now, the warm water\u00a0Karenia brevis<\/em>, which only occurs in the south-eastern United States and also produces brevetoxins, had been considered the most devastating marine HAB species in terms of its environmental, economic and social impacts,\u201d Murray adds.<\/p>\n

Although the harmful algal bloom in South Australia was first detected in March 2025, it hasn\u2019t yet gone away. \u201cThe South Australian HAB still hasn’t completely disappeared about 15 months after it started,\u201d says Murray. \u201cWe now need to fully investigate the factors that cause\u00a0Karenia<\/em>\u00a0to grow and understand its mechanisms of toxicity.\u201d<\/p>\n

This discovery represents \u201can emerging international threat with unknown consequences\u201d they write in the paper. That\u2019s because this new species of\u00a0Karenia,\u00a0<\/em>which is found in cold water, \u201ccould potentially bloom anywhere with similar coastal water conditions,\u201d explains Murray.<\/p>\n

Now, the experts are continuing to study the\u00a0Karenia cristata\u00a0<\/em>in the hope they might find ways to mitigate its harmful impacts to prevent humans or animals getting sick from future blooms.<\/p>\n

However, Murray warns that even the experts won\u2019t be able to prevent dangerous red tides entirely: \u201cA harmful algal bloom is a natural disaster, like a cyclone,\u201d she says, \u201cand we cannot expect to fully control or reverse it.\u201d<\/p>\n

This article<\/a> by Melissa Hobson was first published by Discover Wildlife on 8 July 2026. Lead Image:\u00a0THP Creative \/ Getty Images.<\/em><\/p>\n

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