Ominous blood-like substance off Aussie coast after 9,000 animals die

Yahoo

11-07-2025

An ominous, blood-red substance has been filmed drifting through the sea for metres on end off the South Australian coast this week, as concerns rise in the state over the ongoing toxic algae crisis that has so far been responsible for the deaths of 8,000 to 9,000 marine animals, spanning over 390 species.
Footage shared on social media, attracting thousands of responses among Australians, shows a red, paint-like substance billowing through the ocean off Wirrina Cove, a locality on the Fleurieu Peninsula.
Worried locals responded, questioning what had left the water such a bright red colour. "Whatever it is, I hope it doesn't make any more ocean critters sick or kill them. I worry for the whales that have been seen at Victor Harbour," a woman said.
Authorities in SA continue to grapple with how best to manage the crisis, with experts saying death totals are based on reported observations and are likely underestimates. The bloom, caused by Karenia mikimotoi, has impacted a wide range of marine life, including fish, sharks, rays, invertebrates, and even iconic species like the leafy sea dragon.
Yahoo News Australia questioned the SA Department of Primary Industries and Regions (PIRSA) about the bright red algal bloom at Wirrina Cove. A spokesperson confirmed it is indeed another form of algae — Noctiluca scintillans.
"Noctiluca scintillans is not known to have harmful impacts on marine life," they said.
Noctiluca scintillans, often nicknamed "sea sparkle," is a type of single-celled marine organism known for its bioluminescence — a glow it emits when disturbed by waves or movement in the water. While beautiful at night, during the day it often appears as a red or pinkish bloom, which is why it's sometimes referred to as a "red tide." This red colour comes not from Noctiluca itself, but from the pigments of the tiny plankton it eats and stores inside its body.
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Despite being non-toxic to humans and not producing traditional algal toxins, Noctiluca can still be harmful in high concentrations. Large blooms can deplete oxygen levels in the water as they die and decay, leading to fish kills or marine life stress, especially in enclosed or poorly flushed coastal areas. Additionally, it can disrupt food webs by outcompeting other plankton and altering nutrient dynamics.
Noctiluca blooms are relatively common in Australian waters, especially during warm, calm conditions, and have been observed along coastlines from New South Wales to South Australia. While they attract attention for their visual spectacle, particularly during night-time blooms, their presence can often be an indicator of nutrient imbalance or environmental change in marine ecosystems.
Professor Shauna Murray of the School of Life Sciences at the University of Technology, Sydney, is an expert on algal blooms. In an interview with Yahoo News, she said it's probably "too early to tell" what's causing this apparent nutrient imbalance in southern waters.
"I think it's too early to say exactly what factors are driving this particular harmful algal bloom (HAB) of Karenia mikimotoi," she said.
"Every species of harmful algae has highly individual conditions that it grows under, and these vary. Karenia mikimotoi is normally a temperate species, which blooms in the north of China, the north Atlantic, and other countries.
"However, having said that, it could be that a one-degree increase in water temperatures over an extended time frame could be contributing to the growth of the species. Other conditions, such as currents, water nutrients, and other factors, are also contributing. HABs are almost always due to a specific combination of factors unique to the algal species."
In general, Murray Said, climate change is "certainly having long-term impacts on HABs. "We are seeing HABs extend their range further south, like blooms of Noctiluca scintillans, which now occur into Tasmanian waters, but previously were only found in mainland Australia," she said.
Karenia mikimotoi produce reactive oxygen species that damage gill tissues, leading to suffocation in marine animals, affecting ecosystems along approximately 150 kilometres of coastline, including areas around the Fleurieu Peninsula, Kangaroo Island, and Adelaide's metropolitan beaches.
The situation remains critical, with ongoing monitoring and response efforts by authorities and scientists.
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