Dead sunflower starfish are littering the waters north of Vancouver.

Three years ago, there was a sudden explosion in the number of sunflower starfish off the British Columbia coast. But as quickly as they came, large amounts of the species have recently been found decomposing or dead in the same place they once bloomed.

As these starfish are lethal marine predators, their deaths will have an effect on other marine life, particularly their prey.

“The sunflower starfish is the terror of the shallow seas around here,” says Chris Harley, associate professor of ecology and evolution at the University of British Columbia. “The starfish mortality will allow sea urchins, clams and sea cucumbers to grow in number until the mortality ends.”

There have also been enormous die-offs of the morning sun star, which eats the sunflower starfish. It’s not known whether the deaths of the two species are connected.

The sunflower starfish die-offs were discovered in August. Jonathan Martin, a Canadian scuba diver and marine biologist, was one of the first to see amputated arms of sunflower starfish during a scuba dive (see video below). He initially thought the starfish had lost their arms after getting caught in crab traps. But on a second dive near Whytecliffe Park, he saw decomposing sunflower starfish everywhere, looking like they were melting and disintegrating.

“I was quite taken aback by how bad it looked, how widespread it was.” He noticed several had white lesions on their arms and bodies. Some were weak, half hanging off the rock. “They looked a little deflated and flaccid.”

So far, huge sunflower starfish die-offs have only been seen near the Vancouver area.

While Harley says it’s unusual to see massive die-offs of this species, he notes that large die-offs of other starfish occurred off California’s coast earlier this summer and off the Atlantic Coast last year.

At this point, no one knows the cause of the sunflower starfish’s demise.

Harley says they may have died from a disease or from low salt content in the water. He noticed there were rainstorms in late August and early September, which may have brought freshwater into the sunflower starfish’s territory. He says that starfish aren’t used to the freshwater and may have been in the wrong place at the wrong time. “If it’s severe enough, they can drop their arms, crawl away by themselves and decompose into white nasty goo.”

Early this week, Martin went to Kelvin Grove at the request of Fisheries and Oceans Canada and took a decomposing starfish for government testing. He says the results won’t be in for a few weeks.

“We really don’t know what’s causing this. It may just be the population correcting itself, the bubble bursting,” he says. “We have to be patient and see what the results bring back.”