DOI: 10.5061/dryad.5b2k785
title: Data from: Reciprocal abundance shifts of the intertidal sea stars, Evasterias troschelii and Pisaster ochraceus, following sea star wasting disease

description: 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.
description: EvasteriasPisasterSurvey_Table_2_Fig_1_dataLong 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.Table_2_Fig_1_data.csvTable3_Fig_2_dataBreakdown 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.TableS3_FigS3_dataMean 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.Fig_S4_dataSeasonal 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.