Invasion of the giant blobs

Caleb Clarke measures one of the jellyfish washed up on Great Barrier Island. The biggest measured 1.5m across.

Jellyfish the size of a dining room table have been washed up on Great Barrier Island, leading a scientist to blame pollution for the over-grown monsters.

The purple "lion mane" jellyfish washed up near Blind Bay to the southwest, between Whangaparapara and Tryphena Harbour. The biggest measured 1.5m across and three others were at least 1.2m.

Resident John Mellars, who has lived on the island for almost 20 years, said hundreds of smaller ones were stranded along the beach.

"I've never seen anything like it before, nothing like it," he said.

Marine ecologist Floor Anthoni, said the species was not only rare in New Zealand waters but these specimens were abnormally large. Dr Anthoni runs the Leigh-based Seafriends marine education centre and website and put their growth down to the availability of extra food, but that was not good news.

While jellyfish normally fed on zooplankton, tiny animals near the bottom of the ocean food chain, they can feed on an unusually large, jelly-like form of phytoplankton - the ocean's plant "soup" - called dinoflagellate.

Unseasonable amounts of dinoflagellate were around at the moment, noticeable through the effect of "phosphorescence", or "sea spark" which doesn't usually arrive until late summer.

Scientists believe phosphorescence could be caused by high concentrations of nutrients in the sea from run-off from sewage or other pollutants. "It's a symptom of poor water conditions," Dr Anthoni said.

The purple "bell" on top of the jellyfish was the part that swam while around it are "yellow skirts" which are egg repositories or gonads.

At the outer fringe are the tentacles, which can be extended or contracted.