B.C.'s coastal sea star population in increasingly hot water

Rising ocean temperatures due to climate change could be causing the alarming decline of sea star populations off B.C.'s coast.

That's the conclusion of four years of research into the animals conducted by various organizations, including Cornell University, the Vancouver Aquarium, the University of British Columbia and the University of California.

Jackie Hildering, a biologist based in Port McNeill, B.C., says warmer waters can lead to younger sea stars becoming vulnerable to sea star-associated densovirus, a virus that marine biologists have been aware of for at least seven decades.

Hildering says the predators becoming increasingly susceptible to the disease in recent years led researchers to search for a "stressor" that could be causing the proliferation of the sickness. 

They found that, while it may not be the definitive "stressor," there is a clear correlation between an increase in temperature and the animals succumbing to the disease.

Four years ago, Hildering, who monitors the coast around northern Vancouver Island, saw an unprecedented number of sea star species suddenly dying off.

She wasn't alone in her findings, as 20 species of sea star from Alaska to Mexico were impacted.

"It is totally unprecedented in terms of range, the number of species impacted and how long it has persisted," says Hildering.

Hildering says the ecosystem and biodiversity of B.C.'s waters are now threatened by the lack of sea stars.

She says the animals serve as important predators that keep sea urchin populations in check. Sea urchins eat kelp, and, with fewer sea stars, there are also fewer kelp beds to provide habitats for many forms of ocean life.

"It was so common to see these big beautiful stars at the ocean bottom, big piles of them" says Hildering. "In my last 50 dives, in the last year, I've only seen three adults."

'Zombie-like'

In the Vancouver Island area, specifically, the species worst impacted is the often metre-wide, 20-armed sunflower sea star.

Hildering says the progression of the disease on the sunflower sea star is "horrific" and most are lucky not to see it.

She says as the sickness takes hold the animals begin to contort. Stressed sea stars then release their legs from their bodies as a natural reflex.

"This you can imagine was almost zombie-like," says Hildering. "Seeing the legs crawl away from the sea stars ... Then you would be left with these big piles of mush."

The theory of climate change warming the ocean water and causing the sickness still doesn't account for baby sea stars being spotted every so often.

Hildering's hypothesis, based off prior research and reports from fishermen, is, at depths where the water is colder, there are likely still adult sea stars.

She says that when the animals reproduce they release their sex cells into the water column which leads to infant stars growing in shallow water. As the babies start growing in the warmer shallow water, they succumb to the disease.

Hildering says the ocean's health is a clear indication of global environmental problems.

She adds, to reverse the current sea star situation, humans need to reduce carbon emissions, and, in turn, slow the warming of the ocean.

With files from On the Island