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
From Alaska to California

Since 2013, a wasting disease has caused the sunflower sea star to decline by 80 to 100% across roughly 3,000 km of Northeast Pacific coastline, coinciding with anomalously warm waters — one of the fastest marine predator collapses ever documented.

Documented
Detail

Harvell, C.D., Montecino-Latorre, D., Caldwell, J.M. et al. (2019). Disease epidemic and a marine heat wave are associated with the continental-scale collapse of a pivotal predator (Pycnopodia helianthoides). Science Advances, 5(1), eaau7042.

The authors combine nearly 11,000 shallow-water dive surveys (2006-2017, California to Alaska) with nearly 9,000 deep-water trawl surveys (2004-2016, California to Washington). The peak of the decline coincides with the anomalously warm surface waters of the Pacific "blob" — a sign that disease and thermal stress acted together rather than separately.

In California

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 and forcing the closure of two fisheries.

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 to 1.7 per m² before 2014 to 8.2-12.9 per m² by 2015. The resulting red abalone mortality (48 to 82% between 2016 and 2017, then up to 96% the following year) led 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.

IUCN assessment

A synthesis of more than 61,000 surveys confirms the scale of the disaster across the species' entire range: a 90.6% decline, roughly 5.75 billion individuals lost, and near-total extirpation south of the Strait of Juan de Fuca — to the point that the species is now listed as critically endangered.

Documented
Detail

Gravem, S.A. et al. (2021). Pycnopodia helianthoides. The IUCN Red List of Threatened Species 2021.

The assessment combines 31 datasets and 61,043 surveys conducted between 1967 and 2020, from the Aleutians to Baja California, from the intertidal down to 984 m depth — the most complete synthesis available for this species, confirming at the continental scale what regional studies had already measured locally.

In the fjords, B.C.

Some British Columbia fjords harbor populations that have remained stable thanks to glacial meltwater, which pushes the stars into cooler depths unfavorable to the disease — a natural refuge that could seed recovery, but one that climate change itself threatens by altering these freshwater inputs.

Extrapolated
Detail

Extrapolation à partir de Gehman, A.-L.M. et al. (2025). Fjord oceanographic dynamics provide refuge for critically endangered Pycnopodia helianthoides. Proceedings of the Royal Society B, 292(2044), 20242770 — l'étude documente un mécanisme de refuge actuel, pas encore un rétablissement de l'espèce à l'échelle de son aire.

In the fjords studied, the summer influx of fresh water creates a very low-salinity surface layer that the species avoids, forcing it into colder waters where the disease progresses less readily. Density there remained stable, with large reproductive adults absent elsewhere present by 2023 — but the authors note that climate warming itself threatens this same mechanism by altering glacial melt and Arctic outflow patterns.

What's missing to confirm it: No monitoring yet confirms whether these refuges will, over time, be enough to reseed the collapsed coastal populations rather than merely delaying their own decline.

Documentation

Last verified: August 14, 2026