It has taken them about 100 years, but box jellyfish colonies appear to have spread from Waikiki out to the Wai'anae Coast and that is perhaps the reason why they have begun to show up in large numbers on beaches there eight to 10 days after a full moon, said Waikiki Aquarium Director Andrew Rossiter.

By early yesterday morning, 1,000 of the small sea creatures had been found at Makaha Beach Park and another 500 washed ashore a few miles away at Poka'i Bay in Wai'anae, said Bryan Cheplic, spokesman for the city Emergency Services Department.

Another 400 of the tiny but potentially deadly jellyfish turned up along the South Shore, from Ala Moana Beach Park to Hanauma Bay.

Historically, large numbers of dead or dying box jellyfish have been found along South Shore beaches, Cheplic said. But it was almost unheard of for large numbers of them to show up on West O'ahu beaches, Cheplic said.

"Over the past decade, there were virtually no reports of box jellyfish showing up on the beaches in West O'ahu," Cheplic said.

"Then last month, about 700 washed up at Makaha, and this month the number is up over 1,000," he said.

Cheplic said his officer did not have the authority to shut down the beaches where large numbers of jellyfish were turning up.

But lifeguards were warning would-be swimmers to stay out of the water if they didn't want to risk being stung.

Rossiter said very little is known about box jellyfish "especially given all the negative publicity they get."

"For instance, we don't even know how long they live in their natural environment," Rossiter said.

The number of box jellyfish off the Wai'anae Coast may have reached a "sufficient enough population density" that large numbers washing up on shore after a full moon could become commonplace, he said.

The record for keeping one of the inch-long sea creatures alive in captivity is six weeks and is held by the Waikiki Aquarium, Rossiter said.

"It's almost impossible to replicate conditions in an exhibit but we keep experimenting with ways to extend their life span in captivity," Rossiter said.

Aquarium workers go out on the ocean about two days before the full moon and float a light on top of the water to attract the jellyfish which are then captured and taken to the facility.

"We've had them on display before and will have them again, but we don't have any right know," Rossiter said.

Reach David Waite at dwaite@honoluluadvertiser.com.