Waiheke wonder: A blooming marvellous summer sight

The spectacular but harmless algal bloom swathed Waiheke Island in a red tide. Picture / Kenny Rodger

The sea north of Waiheke Island was radiant yesterday afternoon, as an algal bloom glowed beneath a dull cloudy sky.

Residents grabbed binoculars and marvelled as the swirling patterns of iridescent plankton produced a kaleidoscopic effect.

When darkness fell, gleaming trails of phosphorescence were left behind boats as they cut through patches of bloom, while waders kicked up shining star bursts.

"It's quite neat and it's harmless," said the Auckland Regional Council's environmental research manager, Chris Hatton.

He identified the algal bloom as Noctiluca scintellens, a type of alga often found on the Auckland east coast over summer.

"It's late for it to bloom," he said. "It's usually around spring to early summer.

"They respond to warming seas and rainfall and nutrient run-off from the land."

Mr Hatton said the bloom was one of several summer-blooming plankton. "It's just that this one is bright pink, so everyone can see it."

Slicks of the bloom have been seen in the Hauraki Gulf from Waiheke Island and along the Rodney coast as far north as Mangawhai.

Samples taken in previous years for the council show the centre of the slick is thick and jelly-like.

The council said the bloom was non-toxic - unlike the Karenia and Gymnodinium species found along the Rodney coast in December 2002.

Where high volumes of these algae were present, people reported numb lips after swimming.

The toxic algae also caused thousands of fish to die at Hatfields Beach near Orewa in October 2002.

Although the bloom off Waiheke was harmless to people, the council said boats passing through could suffer clogged engine filters.

It also had an impact on scuba diving.

"It's like swimming in instant pudding," said diver Ivan Blackwell, who runs the glass-bottom boat at the Goat Island Marine Reserve near Leigh.

He said a bloom near the reserve at Christmas had since dispersed.

"But it was not as much, and was later this year - we normally have it at Labour Weekend."

Auckland University scientist Joe Evans, of the Goat Island research laboratory, said light onshore winds caused slicks to form and drift towards land.

He said his children enjoyed rushing into the water at night and coming out glowing like phantoms.