Â鶹ÒùÔº

South Australian beaches have been awash with foamy, discolored water and for months. The problem hasn't gone away; it has spread.

Devastating scenes of death and destruction mobilized locals along the Fleurieu Peninsula, Yorke Peninsula and Kangaroo Island. The state government has hosted , most recently with from around Australia, and issued .

Unfortunately, there are the bloom. Scientists had hoped strong westerly winds would break it up and push it out to sea. But so far, the wild weather has just pushed it through the Murray Mouth . And even if the bloom is washed away this winter, it could return in spring.

This bloom represents a stark warning to coastal communities, as well as tourism, seafood and aquaculture industries. It's a sign of what's to come, in Australia and around the world, as the oceans warm.

An unprecedented algal bloom

The first sign of trouble came in March this year, when dozens of . Many reported sore eyes, coughing or trouble breathing.

Water testing soon : a harmful algal bloom of Karenia mikimotoi.

Most people felt better within hours or days of leaving the beach. But marine life of all kinds was washing up dead or dying.

Fish habitat charity OzFish set up a new to capture the data, using iNaturalist.

OzFish SA project manager Brad Martin the bloom was like an "underwater bushfire," adding: "It's suffocating fish, it's taking the oxygen out of the water and it's producing toxins."

Photos of dead fish, seahorses, octopuses and rays were already on social media. So OzFish encouraged people to start using iNaturalist, to identify the species and capture the data.

The more than 200 species of marine creatures died, including 100 types of fish and sharks. This includes popular recreational fishing species such as flathead, squid, crabs and rock lobsters.

Almost half the deaths were ray-finned fish species. A quarter were sharks and ray species. Then came soft-bodied "cephalopods" such as cuttlefish and octopus, and crustaceans such as crabs, lobsters and prawns.

Most of these species live on or near the sea floor with small home ranges. As in a bushfire, they have little chance of escape. Other fish that live in the open ocean, such as whiting, snapper and tuna, can swim away.

The culprit

K. mikimotoi is a type of microalgae. It and carbon dioxide to grow and divide, releasing oxygen.

In calm conditions, with plenty of light and warmth, the algal cells divide rapidly. Ideal conditions for algal growth are becoming more common as the climate changes and seas warm.

Algal toxins are known to cause illness and sometimes death in , and .

K. mikimotoi is lethal to marine life, not humans. But the toxic effects in marine life are complicated and poorly understood.

The algae irritates , causing cell death and . It also causes , or lack of oxygen in the blood. And when the algae die off, decomposition consumes huge amounts of oxygen—leaving marine life to suffocate.

Scientists now suspect other Karenia species may be involved too, due to the detection of in shellfish. This is the first detection of brevetoxins in Australia.

What can be done?

A marine heat wave is largely to blame. Sea surface temperatures have been 2.5°C warmer than usual since September. Relatively calm conditions, with little wind and small swells, also enabled the bloom to grow. Now it's a matter of waiting for strong westerly winds to blow it all away.

The latest update shows sea surface temperatures have stabilized. But deeper gulf and shelf waters remain 1–2°C above average for this time of the year.

is making future blooms more likely. So tackling climate change is one way to help.

Another is minimizing the runoff of nutrients into waterways. Microalgae can be found anywhere with enough water, light and nutrients. So reducing pollution can help of algal blooms.

This includes better management of fertilizer on farms and in home gardens. Lower levels of nutrients such as will reduce the risk of future blooms in marine and inland waterways.

When it comes to blue-green algae, with freshwater and stirring it up can disperse the colonies and prevent a bloom.

Monitoring is also important. OzFish encourages South Australians to continue providing photo reports via iNaturalist. Any new fish kills should also be .

Microalgae are not all bad

It's worth remembering life on Earth wouldn't exist without microalgae. These tiny organisms produced in the atmosphere today, and play an important role in balanced ecosystems.

The algae is a common dietary supplement. Microalgae are also potentially useful for , as a and for .

Heeding the lessons

Once a harmful algal bloom begins, it will persist for as long as conditions remain suitable.

This bloom already has lasted three months, and there's no guarantee the end is near.

Recovery will be slow, as shown in the and other parts of the world. And the risk of a repeat event is high.

Further research is needed to keep these ancient organisms in check.

This article is republished from under a Creative Commons license. Read the .