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Kay, Sharon; Gehman, Alyssa-Lois; Harley, Christopher

<b>Abstract</b><br/>Disease emergence occurs within the context of ecological communities, and disease driven declines in host populations can lead to complex direct and indirect ecological effects. Varying effects of a single disease among multiple susceptible hosts could benefit relatively resistant species. Beginning in 2013, an outbreak of sea star wasting disease (SSWD) led to population declines of many sea star species along the west coast of North America. Through field surveys and laboratory experiments, we investigated how and why the relative abundances of two co-occurring sea star species, Evasterias troschelii and Pisaster ochraceus, shifted during the ongoing wasting epidemic in Burrard Inlet, British Columbia, Canada. We hypothesized that Evasterias is competitively inferior to Pisaster but more resistant to SSWD. Thus, we predicted that SSWD-induced declines of Pisaster could mitigate the negative effects of SSWD on Evasterias, as the latter would experience competitive release. We document shifts in sea star abundance from 2007-2017: Pisaster abundance and mean size declined during the outbreak, while Evasterias abundance increased from relatively rare to numerically dominant within the intertidal. When exposed to symptomatic sea stars, Pisaster and Evasterias both showed signs of SSWD, but transmission and susceptibility was lower in Evasterias. Despite diet overlap documented in our field surveys, Evasterias was not outcompeted by Pisaster in laboratory trails conducted with the relatively small Pisaster available after the outbreak. Interference competition with larger Pisaster, or prey exploitation by Pisaster during summer when Evasterias is primarily subtidal, may explain the rarity of Evasterias prior to Pisaster declines. Our results suggest that indirect effects mediated by competition can mask some of the direct effects of disease outbreaks, and the combination of direct and indirect effects will determine the restructuring of a community after disturbance.; <b>Usage notes</b><br /><div class="o-metadata__file-usage-entry"><h4 class="o-heading__level3-file-title">EvasteriasPisasterSurvey_Table_2_Fig_1_data</h4><div class="o-metadata__file-description">Long term Evasterias and Pisaster population data in Burrard Inlet, British Columbia, Canada. Percent of maximum abundance (denoted as “percent_max”) for each species and proportion of each species within the sea star community (denoted as “prop_sp”), during winter surveys from 2008 to 2017. Each survey’s percent of maximum abundance was calculated using the maximum abundance recorded for that site during our surveys from 2008 to 2017. Data are split into “pre” and “post” estimated time of outbreak of wasting disease, n = 9 surveys for years before wasting and n = 40 surveys for years after wasting. Surveys are from 5 sites, and estimates of area surveyed at each site are provided. Salinity is opportunistically reported.</div><div class="o-metadata__file-name">Table_2_Fig_1_data.csv</br></div></div><div class="o-metadata__file-usage-entry"><h4 class="o-heading__level3-file-title">Table3_Fig_2_data</h4><div class="o-metadata__file-description">Breakdown of disease progression in Evasterias and Pisaster over 28 days, in terms of number of asymptomatic (“num_healthy”) and the number of surviving individuals remaining in a tank “(num_alive”), after experimental exposure to conspecifics with signs of SSWD. “Day” indicates the duration of experiment and “tank” indicates the replicate tanks of initially uninfected sea stars. “Census_sick” and “census_dead” indicates a binary assignment of 0 or 1, where 0 denotes more than half the population of 5 sea stars is healthy/alive and 1 denotes more than half the population is sick/dead. See supplement S1.2 for more details on the methods of the experiments.</div><div class="o-metadata__file-name"></div></div><div class="o-metadata__file-usage-entry"><h4 class="o-heading__level3-file-title">TableS3_FigS3_data</h4><div class="o-metadata__file-description">Mean percent change in wet weight (grams) across competition treatments, from all three experiment rounds. Competition treatments are labeled by the number of sea stars held in a tank, and of what species. Evasterias is abbreviated with “Eva” and Pisaster is abbreviated with “Pi”. The interspecific treatment for Evasterias response was “Eva (2 Eva + 2 Pi)” and for Pisaster response was “Pi (2 Eva + 2 Pi)”. Each treatment was replicated three times per experiment (denoted as “tank” number), with the exception of experiment three, where the interspecific treatment was replicated four times, for a total of 9 replications and 10 replications respectively across all three experiments. Sample size varied per treatment as some sea stars developed signs of SSWD and thus were removed and replaced with uninfected sea stars. Replacement sea star weights were not included in the data set or growth analysis. For more details on the methods see supplement section S1.3.</div><div class="o-metadata__file-name"></div></div><div class="o-metadata__file-usage-entry"><h4 class="o-heading__level3-file-title">Fig_S4_data</h4><div class="o-metadata__file-description">Seasonal abundance data for Pisaster and Evasterias for April 2016 to March 2017. Mean percent of maximum abundance (denoted as “percent_max”) and mean proportion of species in community (denoted as “prop_sp”), over the months of one year. Each survey’s percent of maximum abundance was calculated using the maximum abundance recorded for that site during our surveys in 2016/2017.Surveys are from 5 sites, and estimates of area surveyed at each site are provided. Salinity is opportunistically reported. See supplement section S1.1 for more details on the methods.</div><div class="o-metadata__file-name"></div></div>

Canada; British Columbia; Burrard Inlet

Dryad version number: 1</p>

Version status: submitted</p>

Dryad curation status: Published</p>

Sharing link: https://datadryad.org/stash/share/SmVDvGLAtqS5M84cePfsV1CBH0L_TQi3OKSua6tyBAQ</p>

Storage size: 65843</p>

Visibility: public</p>

University of British Columbia Library

10.14288/1.0398019

https://doi.org/10.5683/SP2/YGSHU6; https://doi.org/10.5061/dryad.5b2k785

https://creativecommons.org/publicdomain/zero/1.0/