Why is 'cornflake' seaweed piling up on Port Macquarie beaches?

Not uncommon at this time of year, the seaweed turns the normally bright blue surf to a dark red.

Giving a pungent smell, swimmers and surfers often mention that this particular type of small seaweed gets caught in hair and teeth. There were large blooms on Hastings beaches in 2005 and 2019.

Local surfing legend Wayne 'Huddo' Hudson runs Port Macquarie Surf School at Flynns Beach and said while it smells bad, he is used to it.

"You just surf through it. It comes every year at summer it's just that this year it's bad," he said.

"2019 was bad and 2005 was horrendous when they had the bulldozers and stuff down here so it's not as bad as that. It's just there, it happens every summer."

On days where the seaweed clogs up the shoreline Mr Hudson said surfing is harder, especially for juniors.

"We had a school sport class yesterday and it was thicker than today," he said. "It was chunky and I just gave them the option as I was thinking 'you won't want to get in'.

"We did a vote, do you want to hop in or do other stuff, we had alternatives arranged, but we had 18 vote to hop in so eight didn't.

"At school sport this morning there were four girls and the other 40 kids hopped in so it was okay."

Mr Hudson said the small 'cornflake' seaweed will shift with the tides and often thin out in the afternoon.

However, surf school staff member Emma Marchant said by that time the damage has been done.

"It gets everywhere all the time. The bottom of my shower is caked in it and it just gets in your hair and makes everything smell," she said.

The red or brown seaweed colloquially known as cornflake seaweed is called Colpomenia.

Marine science Professor Nick Paul from the University of the Sunshine Coast said the blooms are common in spring as the water warms up and the days get longer. The algae starts off larger before breaking up into smaller cornflake-sized pieces.

"These ones are normally attached and then get dislodged in swell and can keep growing when they are floating in the water column," he said.

"They will break down and be consumed by beach hoppers and other critters. Ultimately the nutrients will cycle back into the ocean."

Professor Paul said there is nothing harmful or toxic about the seaweed.

In December 2019 a woman running on a Gold Coast beach had to be rescued after becoming stuck in cornflake seaweed piled up thigh-high on the shoreline.

The bloom, described by a marine biologist as unprecedented, took more than a month to decompose.

As for any health benefits of the Colpomenia?

"Not that I know of from this one. The Colpomenia (are) not an edible species, so not much research has been done on potential food or human benefits," Professor Paul said.

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