Disease-driven mass mortality event leads to widespread extirpation and variable recovery potential of a marine predator across the eastern Pacific

The prevalence of disease-driven mass mortality events is increasing, but
our understanding of spatial variation in their magnitude, timing, and
triggers are often poorly resolved. Here, we use a novel range-wide
dataset comprised of 48,810 surveys to quantify how Sea Star Wasting
Disease affected Pycnopodia helianthoides, the sunflower sea star, across
its range from Baja California, Mexico to the Aleutian Islands, USA. We
found that the outbreak occurred more rapidly, killed a greater percentage
of the population, and left fewer survivors in the southern half of the
species’ range. Pycnopodia now appears to be functionally extinct
(> 99.2% declines) from Baja California, Mexico to Cape Flattery,
Washington, USA and exhibited severe declines (> 87.8%) from the
Salish Sea to the Gulf of Alaska. The importance of temperature in
predicting Pycnopodia distribution rose 450% after the outbreak,
suggesting these latitudinal gradients may stem from an interaction
between disease severity and warmer waters. We found no evidence of
population recovery in the years since the outbreak. Natural recovery in
the southern half of the range is unlikely over the short-term and
assisted recovery will likely be required for recovery in the southern
half of the range on ecologically-relevant time scales.