What If Gone

Species → Sunflower sea star

Sunflower sea star

Pycnopodia helianthoides

A 90.6% range-wide decline between 2013 and 2020, representing an…
Extinction risk Critically Endangered
Apex predatorKeystone speciesMarine environmentCatastrophic declineClimate change
Sunflower sea star (Pycnopodia helianthoides)
Photo: Mike Baird, Wikimedia Commons (CC BY 2.0)

What if it disappeared?

Impact Major
1 year

Without the sunflower star to keep them in check, purple sea urchins increased 60-fold in a single year in northern California, wiping out 95% of bull kelp canopy across more than 350 km of coastline.

Documented
Detail

Rogers-Bennett, L. et Catton, C.A. (2019). Marine heat wave and multiple stressors tip bull kelp forest to sea urchin barrens. Scientific Reports, 9, 15050.

Purple urchin density rose from 0-1.7 per m² before 2014 to 8.2-12.9 per m² by 2015 — an explosion concentrated within a single season, immediately following the sunflower star's collapse in the region.

10 years

That urchin explosion was no isolated blip: the resulting red abalone mortality climbed to 96% the following year, and two fisheries worth nearly $47 million a year combined — recreational abalone, commercial red urchin — were forced to close.

Documented
Detail

Rogers-Bennett, L. et Catton, C.A. (2019). Marine heat wave and multiple stressors tip bull kelp forest to sea urchin barrens. Scientific Reports, 9, 15050.

Red abalone mortality rose from 48 to 82% between 2016 and 2017, then up to 96% the following year, leading to the 2018 closure of the recreational abalone fishery ($44 million a year) and the collapse of the commercial red sea urchin fishery ($3 million a year) starting in 2015.

100 years

Over a century, if this coastline stayed without the sunflower star, this urchin-dominated state would likely persist rather than reverting to kelp forest on its own: once such an ecosystem has flipped, urchins can survive very long stretches without much food, which makes this kind of shift especially hard to reverse without intervention.

Hypothesis
1000 years

Over a thousand years, the picture would likely be uneven: in fjords where glacial meltwater keeps the disease at bay, pockets of kelp sustained by a still-present sunflower star could have persisted, while elsewhere, across the thousands of kilometers of affected coastline, urchins would likely remain in control.

Hypothesis

Documentation

Last verified: August 16, 2026