Sunflower sea star die-off could result in larger ecosystem level consequences

New research on the sunflower sea star highlights the importance of monitoring our ecosystems over time.

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Since 2013, more than 20 sea star species from Mexico to Alaska have been affected by a sea star wasting disease. The sunflower sea star in particular, is among the worst hit. The outbreak has alarmed scientists as this sea star is an important predator in coastal food webs.

A new study by scientists, including SFU professor Anne Salomon and her PhD students Jenn Burt and Lynn Lee, provides evidence of the continental-wide extent of this sea star disease epidemic and links it to the occurrence of an anomalously warm water heat wave.

Diver and trawl surveys conducted from California to Alaska have revealed an alarmingly 80 to 100% decline in sea star populations over the past decade. The study found that increased warm sea surface temperatures is strongly associated with the marine infectious disease outbreak, coinciding with peak declines of the sunflower sea star.

Sunflower sea stars, which are commonly found in the northeast Pacific, are important predators of small and medium sized sea urchins.

“At the bottom of the ocean, on the central coast of BC and Haida Gwaii, sunflower sea stars could get as big as hula hoops,” said Salomon. “We would easily see anywhere between 10 to 25 of them roaming the sea floor on a typical 45min dive.”

In British Columbia, their population decline is associated with an increase in urchin numbers, and a 30% decline in kelp forests.

Sea Urchins - Mark Wunsch/Greencoast Media

“Sea urchins are like little spikey kelp-munching pacmans,” said Burt. “Around the world, when their populations become abundant, they have caused kelp forests to collapse.”

As the main diet of sea urchin, kelp forests are an important ecosystem, serving as a source of food, oxygen and cover for a diversity of marine wildlife.

“With so many sunflower sea stars gone, kelp forests become more vulnerable to sea urchin grazing and that can have ripple effects across food webs in ways that we have yet to fully understand,” said Salomon.

Kelp - Mark Wunsch/Greencoast Media