A mysterious yellow foam

It all started back in March, when dozens of surfers at beaches outside Gulf St Vincent, about an hour south of state capital Adelaide, reported experiencing a sore throat, dry cough and blurred vision after emerging from the sea.
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Shortly after, a mysterious yellow foam appeared in the surf. Then, dead marine animals started washing up.

Scientists at the University of Technology Sydney soon confirmed the culprit: a buildup of a tiny planktonic algae called Karenia mikimotoi. And it was spreading.
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In early May, the government of Kangaroo Island, a popular eco-tourism destination, said the algal bloom had reached its coastline. A storm at the end of May pushed the algae down the coast into the Coorong lagoon. By July, it had reached the beaches of Adelaide.

Diverse algae are essential to healthy marine ecosystems, converting carbon dioxide into oxygen and benefiting organisms all the way up the food chain, from sea sponges and crabs to whales.

But too much of one specific type of algae can be toxic, causing a harmful algal bloom, also sometimes known as a red tide.

While Karenia mikimotoi does not cause long-term harm to humans, it can damage the gills of fish and shellfish, preventing them from breathing. Algal blooms can also cause discoloration in the water and block sunlight from coming in, harming ecosystems.

The Great Southern Reef is a haven for “really unique� biodiversity, said Bennett, a researcher at the University of Tasmania, who coined the name for the interconnected reef system which spans Australia’s south coast.

About 70% of the species that live there are endemic to the area, he said, meaning they are found nowhere else in the world.

“For these species, once they’re gone, they’re gone.�