Award: OCE-1737372

Extreme disturbances are expected to increase in frequency and intensity with climate change; their consequences for marine species will depend upon the often-enigmatic interplay of dispersal and selection (and drift). This project sought to understand the population and genomic consequences of a decimating epizootic of the sea star Pisaster ochraceus. Existing collections, which immediately preceded and followed the outbreak and documented >90% mortality of adults and massive subsequent recruitment, was coupled with continuing annual surveys and population genomic, transcriptomic, and candidate locus analyses. The project aimed to determine the extent to which this disease outbreak may (or may not) lead to long-term changes in the frequencies of alleles associated with survival of SSWD. Understanding the consequences of large perturbations set against a backdrop of geographic heterogeneity and gradual environmental change is an emerging contemporary issue. It requires long- term characterization of population dynamics, genetic consequences, and future implications. In 2013, sea star wasting disease (SSWD) swept through P. ochraceus populations in the northeastern Pacific. We captured this epizootic in long-term ecological-genetic studies, which documented median 90% mortality coast-wide (site-specific rates 51–96%). In the aftermath of the initial outbreak, we quantified the largest influx of new recruitments on record. The disease currently persists at low-levels among surviving populations, and recruitment continues to be above average but very spatially variable. Given heterogeneity in the environment and in mortality rates, and because the 2013 recruits may have been spawned by adults pre-outbreak, we consider 2014- to-current recruits as progeny of adults that survived the initial wasting period. Genetic assays of these recruits was the basis the assessment of the genomic consequences of the outbreak and may provide the implications for future population and disease dynamics. This project built on long-term field studies of wild populations of P. ochraceus to describe population dynamics, the disease, and genomic diversity. Goals were to discover genetic variation associated with SSWD and to dissociate that variation from population genomic effects attributable to abiotic environmental variation. Objectives were: (1) Census P. ochraceus at 24 sites throughout its range to describe population dynamics, the prevalence of SSWD, and measure abiotic variables. (2) Conduct laboratory experiments coupled with RNAseq analyses to determine loci differentially regulated during exposure to SSWD, temperature, salinity, and pCO2 anomalies. (3) Map ddRAD, RNAseq, and candidate loci under selection to a P. ochraceus genome. (4) Conduct range-wide population genomic analyses for 3 years, including intensive study of a focal region, in which we will assess genetic (RAD) variation among wild-caught specimens with versus without SSWD and experiencing the geographic mosaic of abiotic variation. (5) Explore links between SSWD and candidate loci, such as EF1A. Results were consistent with an association between SSWD, very high mortality (90%), and differential susceptibility of P. ochraceus linked to variation in ddRAD markers, expression of RNAseq loci, and overdominance at a candidate locus (EF1A). RAD analyses showed site specific differences between P. ochraceus adults despite high gene flow, and while intertidal juveniles and adults were selected by SSWD in 2013, the subsequent pulse of new recruits was most genetically similar to the pre-outbreak population. The consequences of the SSWD outbreak are still unfurling in a dynamic eco- evolutionary landscape. With respect to Broader Impacts, the project trained a postdoc, graduate students and many undergraduates including 6 REU students at UC Santa Cruz. Undergraduates participated in both field and laboratory research, and were involved in outreach activities addressing environmental change. UCM and UCSC are designated Hispanic Serving Institutions. Of the 6 REU interns over the course of this project, three were from under-represented groups. Of the six, five (including all 3 that were from under-represented groups) have gone on to graduate school or are employed as a marine ecologists. Over the course of the project we have co-developed citizen science projects and also eduacation modules (Real Data for Distance Learning) for schools to use during the period of remote learning (see marine.ucsc.edu). UCSC MARINe currently maintains a website and interactive map for tracking the incidence of sea star wasting (www.seastarwasting.org), which we will continue to maintain and update throughout the project. This website will provide information to the interested public as well as a nexus for information exchange between scientific colleagues, as it provides a mechanism for almost anyone using rigorous scientific methods to contribute observations. In addition to the website, the general public will learn of our work through the outreach efforts of the Seymour Marine Discovery Center (http://seymourcenter.ucsc.edu/) located on UCSC’s Coastal Science Campus. The MARINe website has been expanded to allow citizen science reports of seastar recruitment to be submitted, vetted and included in the database. In addition, the Seymour center at UCSC (a public outreach facility) has continued present information to the public concerning seastar wasting, recovery, impact on communities and potential causes. Last Modified: 06/23/2022 Submitted by: Peter T Raimondi