Alarm in Australia: a toxic algae proliferate for the anomalous heat and massacres of 200 marine species

Since March 2025, the waters of southern Australia have been the scene of a phenomenon that is attracting the attention of scientists and authorities from all over the world. A massive alga flowering Karenia Mikimotoitoxic for fish fauna, is altering the marine ecosystem, inducing the death of hundreds of aquatic creatures.

“It is a greater flowering than we have ever seen before,” he said Susan CloseMinister of the Environment of Southern Australia, as ABC News Australia explains. “It is not very far from the size of Kangaroo Island and in some parts it reaches the depth of 20 meters”. To understand the scope of the phenomenon, just think that the island of the kangaroos is the third largest island in Australia, with an area of ​​over 4,400 square kilometers.

What is happening to the marine ecosystem?

The first signs of the problem date back to March, when the swimmers reported the presence of a thick foam on the surface of the water and the discovery of marine animals who died on the beaches of Waitpinga and Parsons, in the Fleurieu peninsula. Since then, the phenomenon has quickly extended, reaching Kangaroo Island, the Yorke peninsula and the beaches south of Adelaide.

According to the data collected by theenvironmental organization Ozfishwhich analyzed over 1,400 reports from citizens, more than 200 marine species have been affected by the phenomenon. The numbers tell us that 47% of the dead animals are fish with rooted fins, 26% are sharks and races, 7% are cephalopods (squid, cuttlefish and octopus) while 6% are crustaceans (crabs, lobsters and prawns).

“It’s like witnessing a horror film that is taking place underwater,” he explained to the Guardian Brad Martinresponsible for Ozfish for southern Australia. “Alga Karenia Mikimotoi acts as a toxic blanket that suffocates marine life. It can obstruct the gills of fish by preventing them from breathing, causing bleeding by attacking red blood cells and even damaging the nervous system of marine animals, causing anomalous behaviors”.

Particularly alarming was the recent series of unusual finds: last Monday a white shark was found dead on the popular Henley beach, in Adelaide, while in April two other sharks died in Port Willunga and Port Morowie were reported. These sightings have aroused great concern among experts, considering the rarity of similar events.

The effects on the environment and on man

The Department of primary industries and regions (Purso) of southern Australia has confirmed that algal blooms of this dimensions are extremely rare in the region, with the latest significant episode recorded in Coffin Bay in 2014.

The marine biologist Mike Bossley He documented unusual behaviors in local marine fauna. “We have observed much more active and aggressive races and sharks than normal,” he told ABC News. This observation was dramatically confirmed when, last week, a researcher was focused on an eagle while studying the effects of algae on the marine ecosystem in the Yorke peninsula.

The teacher Shauna Murray of the University of Technology of Sydney, who analyzed the algae under a microscope and studied its DNA, explained that Karenia Mikimotoi is one of the approximately 100 known nocive algae species, each with different toxic effects. “It is believed that this particular species produces reactive oxygen that damages the branchic cells of the fish, preventing them from breathing correctly,” he specified.

Even if the alga is not considered toxic to man directly, it can cause allergic reactions. Several surfers reported symptoms such as persistent cough, eyes irritation and clouded view after coming into contact with contaminated waters. The local health authorities have spread a clear notice: “If you see foam on the beach or notice alterations in the color of the water, you are far away, do not enter,” Minister Close recommended. “And if you have been there, wash carefully.”

The causes and possible solutions

Scientists agree in identifying the main cause of the phenomenon: An unprecedented sea heat wavewith water temperatures 2.5 degrees higher than the seasonal average. This anomalous heating, probably linked to climate change, combined with particularly stable ocean conditions (few winds and small waves), has created the ideal environment for the proliferation of the alga.

The teacher Martina DoblinOceanografa of the Sydney University of Technology specialized in algal blooms, has highlighted a peculiar feature of Karenia Mikimotoi: “It is an unusual alga that can feed on both sunlight and other organisms. In normal conditions it is part of the natural food network, but when proliferate in an uncontrolled way it can become extremely problematic“.

Unfortunately, according to experts, there are no effective human interventions to counter the phenomenon. “The only thing that will interrupt this algal flowering is a significant change in weather conditions, with the arrival of strong western winds,” explained Minister Close. “Usually this happens towards the end of April, but this year it has not yet happened.”