Data associated with: Minor genetic consequences of a major mass mortality: Short-term effects in Pisaster ochraceus

Mass mortality events (MMEs) are increasing globally in frequency and
magnitude, largely due to human-induced change. The effects of these MMEs,
both in the long- and short-term, are of imminent concern because of their
ecosystem impacts. Genomic data can be used to reveal some of the
population-level changes associated with MMEs. Here, we use
reduced-representation sequencing to identify potential short-term genetic
impacts of an MME associated with a sea star wasting (SSW) outbreak. We
tested for changes in the population for genetic differentiation,
diversity, and effective population size between pre-SSW versus post-SSW
populations of Pisaster ochraceus — a species that suffered high
SSW-associated mortality (75–100% at 80% of sites). We detected no
significant population-based genetic differentiation over the spatial
scale sampled, however, the post-SSW population tended toward more
differentiation across sites than the pre-SSW population. Genetic
estimates of effective population size (Ne) did not detectably change,
consistent with theoretical expectations; however, rare alleles were lost.
While we were unable to detect significant population-based genetic
differentiation or changes in Ne over this short time period, the genetic
burden of this MME may be borne by future generations, unless widespread
recruitment mitigates the population decline. Prior results from P.
ochraceus indicated natural selection played a role in altering allele
frequencies following this MME. In addition to the role of selection found
in a previous study on the genomic impacts of SSW on P. ochraceus, our
current study highlights the potential role the stochastic loss of many
individuals plays in altering how genetic variation is structured across
the landscape. Future genetic monitoring is needed to determine long-term
genetic impacts in this long-lived species. Given the increased frequency
of MMEs, it is important to implement demographic and genetic monitoring
strategies that capture baselines and background dynamics to better
contextualize species’ responses to large perturbations.