Disease outbreaks can have substantial impacts on wild populations, but the often patchy or
anecdotal evidence of these impacts impedes our ability to understand outbreak dynamics.
Recently however, a severe disease outbreak occurred in a group of very well-studied
organisms±sea stars along the west coast of North America. We analyzed nearly two
decades of data from a coordinated monitoring effort at 88 sites ranging from southern British
Columbia to San Diego, California along with 2 sites near Sitka, Alaska to better understand
the effects of sea star wasting disease (SSWD) on the keystone intertidal predator,
Pisaster ochraceus. Quantitative surveys revealed unprecedented declines of P. ochraceus
in 2014 and 2015 across nearly the entire geographic range of the species. The intensity of
the impact of SSWD was not uniform across the affected area, with proportionally greater
population declines in the southern regions relative to the north. The degree of population
decline was unrelated to pre-outbreak P. ochraceus density, although these factors have
been linked in other well-documented disease events. While elevated seawater temperatures
were not broadly linked to the initial emergence of SSWD, anomalously high seawater
temperatures in 2014 and 2015 might have exacerbated the disease's impact. Both before
and after the onset of the SSWD outbreak, we documented higher recruitment of P. ochraceus
in the north than in the south, and while some juveniles are surviving (as evidenced by
transition of recruitment pulses to larger size classes), post-SSWD survivorship is lower than during pre-SSWD periods. In hindsight, our data suggest that the SSWD event defied
prediction based on two factors found to be important in other marine disease events, sea
water temperature and population density, and illustrate the importance of surveillance of
natural populations as one element of an integrated approach to marine disease ecology.
Low levels of SSWD-symptomatic sea stars are still present throughout the impacted range, thus the outlook for population recovery is uncertain.
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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 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's range. Pycnopodia now appears to be functionally extinct (greater than 99.2% declines) from Baja California, Mexico to Cape Flattery, Washington, USA and exhibited severe declines (greater than 87.8%) from the Salish Sea to the Gulf of Alaska. The importance of temperature in predicting Pycnopodia distribution rose more than fourfold after the outbreak, suggesting latitudinal variation in outbreak severity 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. Thus, assisted recovery will probably be required to restore the functional role of this predator on ecologically relevant time scales.
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- Award ID(s):
- 2023664
- NSF-PAR ID:
- 10295544
- Date Published:
- Journal Name:
- Proceedings of the Royal Society B: Biological Sciences
- Volume:
- 288
- Issue:
- 1957
- ISSN:
- 0962-8452
- Page Range / eLocation ID:
- 20211195
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1098/rspb.2021.1195
