Sea star death triggers ecological domino effect

In the summer of 2013, millions of sea stars along the West Coast contracted a wasting disease and died in one of the largest wildlife mass mortality events ever recorded. In B.C., the sunflower star was among the most affected. At one metre in diameter, this formerly abundant species is one of the largest sea stars in the world and a voracious predator of invertebrates.

"Howe Sound lost nearly 90 per cent of its sunflower stars in a matter of weeks," says Schultz, a SFU master's student and the Vancouver Aquarium's Howe Sound research program manager. By repeating underwater surveys done before the mass mortality, the researchers were able to measure changes in marine animal and plant communities around the Sound.

They found that green sea urchins, the sunflower stars' favourite prey, have quadrupled since the sea stars disappeared, while kelp, the sea urchins' favourite food decreased by 80 per cent.

"This is a very clear example of a trophic cascade, which is an ecological domino effect triggered by changes at the end of a food chain, says Côté. "It's a stark reminder that everything is connected to everything else. In this case, the knock-on consequences were predictable, but sometimes they are not."

Two summers on, there is still no sign of recovery in sea stars. Until they return, it seems that little will keep urchins in check and their feast on kelp is likely to continue.

The study published in PeerJ, was a joint effort between SFU and the Vancouver Aquarium.