ECB-ART-44664PLoS One 2016 May 04;115:e0153994. doi: 10.1371/journal.pone.0153994.
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Sea Star Wasting Disease in the Keystone Predator Pisaster ochraceus in Oregon: Insights into Differential Population Impacts, Recovery, Predation Rate, and Temperature Effects from Long-Term Research.
Sea star wasting disease (SSWD) first appeared in Oregon in April 2014, and by June had spread to most of the coast. Although delayed compared to areas to the north and south, SSWD was initially most intense in north and central Oregon and spread southward. Up to 90% of individuals showed signs of disease from June-August 2014. In rocky intertidal habitats, populations of the dominant sea star Pisaster ochraceus were rapidly depleted, with magnitudes of decline in density among sites ranging from -2x to -9x (59 to 84%) and of biomass from -2.6x to -15.8x (60 to 90%) by September 2014. The frequency of symptomatic individuals declined over winter and persisted at a low rate through the spring and summer 2015 (~5-15%, at most sites) and into fall 2015. Disease expression included six symptoms: initially with twisting arms, then deflation and/or lesions, lost arms, losing grip on substrate, and final disintegration. SSWD was disproportionally higher in orange individuals, and higher in tidepools. Although historically P. ochraceus recruitment has been low, from fall 2014 to spring 2015 an unprecedented surge of sea star recruitment occurred at all sites, ranging from ~7x to 300x greater than in 2014. The loss of adult and juvenile individuals in 2014 led to a dramatic decline in predation rate on mussels compared to the previous two decades. A proximate cause of wasting was likely the "Sea Star associated Densovirus" (SSaDV), but the ultimate factors triggering the epidemic, if any, remain unclear. Although warm temperature has been proposed as a possible trigger, SSWD in Oregon populations increased with cool temperatures. Since P. ochraceus is a keystone predator that can strongly influence the biodiversity and community structure of the intertidal community, major community-level responses to the disease are expected. However, predicting the specific impacts and time course of change across west coast meta-communities is difficult, suggesting the need for detailed coast-wide investigation of the effects of this outbreak.
PubMed ID: 27144391
PMC ID: PMC4856327
Article link: PLoS One
Genes referenced: LOC100887844 LOC100893907
Article Images: [+] show captions
|Fig 1. Map of study sites along the Oregon coast.Subtidal bathymetry is shown with gray lines, and scaled in m depth.|
|Fig 2. Wasting frequency at nine (eight in 2015) sites spread across three capes in 2014 and 2015.A. and D., CF = Cape Foulweather; B. and E., CP = Cape Perpetua; and C. and F., CB = Cape Blanco. Note that the y-axis scale varies among capes for 2015 data. See Fig 1 for site names, here coded as initials.|
|Fig 3. Frequency of small/juvenile P. ochraceus with wasting compared to frequency of adult P. ochraceus with wasting, averaged across sites within capes (± 1 SE).Asterisks indicate months in 2014 in which juveniles had lower % wasting, and matched pairs statistics indicate overall differences across months within capes. Data were sine-1 square root-transformed for analysis. If September data are dropped for CB, t = 3.33, p = 0.004, n = 11.|
|Fig 4. Frequencies of sea star wasting symptoms for P. ochraceus through time, summer 2014, at 9 sites.Top row = Cape Foulweather sites, middle row = Cape Perpetua sites, and bottom row = Cape Blanco sites. See Fig 1 caption for site names.|
|Fig 5. Decline in adult and juvenile P. ochraceus density, spring and summer 2014, at six sites.Differences in overall average densities (ln-transformed data in a 2-way ANOVA testing site and month without interaction term) are shown by lower case letters in legend, where sites sharing the same letter were not different at p > 0.05.|
|Fig 6. Magnitude of change from summer 2014 to summer 2015 in density (number/m2) of P. ochraceus at seven sites.Sites are color coded by cape, with blue = Cape Foulweather, red = Cape Perpetua, and green = Cape Blanco. A. Change in adult density, B. Change in juvenile density, C. Change in recruit density, D. Change in total sea star density. Weight ranges for each life history stage are approximate, and based on Menge 1974, which found that animals up to ~70g were non-reproductive and animals from ~100 g and larger had ripe gonads (before spawning). See Fig 2 caption for site names.|
|Fig 7. Average (+ 1SE) proportion of recruits of P. ochraceus over time at seven sites.Sample sizes were ~200 individuals per site per sample date. See Methods for details.|
|Fig 8. Size frequencies of P. ochraceus from 2012 to 2015 at three representative sites, one per cape.Samples were taken in spring (black bar) and summer (white bar) in each year except for Boiler Bay, where high wave action prevented collection of the summer 2015 sample. Sample size was ~200. Mean wet weight (± 1 SE) is shown for each sample date.|
|Fig 9. Annual average (± 1SE) number of P. ochraceus settlers at four sites.Vertical dashed line indicates the onset of SSWD.|
|Fig 10. Comparison of predation rate on mussels, Mytilus californianus, in summer 2014 compared to rates averaged across 1990–2013 at six sites.Numbers above each pair of bars show the magnitude of decrease in predation rate.|
|Fig 11. Air and water temperatures by month at three sites.Fogarty Creek and Cape Blanco North climatologies (black lines) were averaged from 1999 to 2014, and at Strawberry Hill from 1993 to 2014. The red line shows 2014 data. Climatologies are monthly means ± 1 SD and 2014 data are monthly means ± 1 SE.|
|Fig 12. Log-linear regression between water temperature averaged over the previous two weeks of the sample date and the frequency (arcsin-transformed) of SSWD on the sample date.|
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