The massive die-off of sea stars along North America's west coast has triggered a domino effect in the region's marine ecology, a new study revealed.
In summer 2013, millions of these echinoderms contracted a deadly virus and died in one of the major wildlife mass mortality events ever documented.
Now, years later, scientists report that the devastating die-off has resulted in the disappearance of kelp forests in British Columbia's Howe Sound.
Mysterious Wasting Disease
The formerly abundant sunflower star was among the species severely affected by the wasting disease, a team of marine ecologists from Simon Fraser University (SFU) found.
Howe Sound lost almost 90 percent of its sunflower stars in just a matter of weeks, says Jessica Schultz, one of the researchers of the study and a research program manager at Vancouver Aquarium.
Schultz says marine divers told them three years ago that sea stars were basically "falling apart" before their very eyes.
Domino Effect
Sunflower stars, which are one of the biggest starfish in world, typically feed off invertebrates such as green sea urchins.
According to scientists, sunflower stars are so feared by green sea urchins that previous studies found this prey scuttles away at the mere scent of the sunflower star's arm.
Schultz says sunflower stars "eat pretty much anything they can get ahold of."
But with their predators nearly wiped out, the population of green sea urchins quadrupled in 20 sites that researchers surveyed.
In turn, these green sea urchins have diminished kelp in Howe Sound by 80 percent, creating what scientists call "urchin barrens."
Indeed, without the sunflower stars to deter them, the green sea urchins were free to graze the kelp forests, clearcutting the underwater ecosystem, says Schultz.
She says the phenomenon is heartbreaking, especially when you're used to seeing luscious kelp beds, but they are now bare rock filled with urchins.
Isabelle Côté, Schultz's co-researcher, says the effect is a clear example of a "trophic cascade," an ecological domino effect provoked by changes at the end of a food chain.
"It's a stark reminder that everything is connected to everything else," says Côté.
In this case, she says, the knock-on consequences of the sea star die-off were predictable. However, in most situations, they are not.
Saving The Marine Ecosystem
Researchers believe that understanding the importance of kelp to underwater communities is vital to keep them safe. These large seaweeds act as habitat for spot prawns and other marine creatures.
"Anything we can do to help understand how the system works, even as it's changing, it's going to allow us to make better management decisions," says Schultz.
Sea stars still haven't recovered from their population loss, but until their return, scientists will keep green sea urchins in check as their feast on kelp will probably continue.
Details of the SFU study are featured in the journal PeerJ.
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