Genomics help track and improve resilience to sea star wasting disease

The sunflower sea star (Pycnopodia helianthoides), once abundant along the Pacific Coast of North America, has suffered catastrophic declines due to sea star wasting disease (SSWD). This devastating syndrome has reduced populations by over 90% in the past decade, earning the species a critically endangered status. As a keystone predator that once helped to manage sea urchin populations, the loss of sunflower sea stars has disrupted kelp forest ecosystems. To address this crisis, researchers are turning to genomics to better understand the disease and explore recovery solutions.

This project, led by Drs. Michael Dawson and Lauren Schiebelhut at the University of California, Merced, aimed to develop genomic tools to understand SSWD vulnerability and resilience in sunflower sea stars. Importantly, the team successfully produced a chromosome-scale reference genome for P. helianthoides, a foundational resource for further genetic studies. Using limited available samples, they also identified genetic markers potentially linked to SSWD. By comparing pre- and post-SSWD populations, they highlighted 51 loci associated with genetic susceptibility. Although sample constraints limited the scope of this analysis, newly discovered tissue samples from Alaska and additional paired pre- and post-wasting specimens offer opportunities for more robust future studies.

In addition, the team documented patterns of genetic diversity using whole-genome sequencing data from contemporary samples, historical museum specimens, and pre-SSWD samples (Fig. 2). This analysis showed that pre-wasting populations in California are most similar to post-wasting populations in Washington. However, gaps remain without samples from Oregon that may distort genetic comparisons. These findings suggest geographic differences in diversity, warranting further investigation.

Interestingly, the team uncovered significant genetic differences linked to sex, with varying sex ratios between fjord and outer coast populations (see figure below). While the project faced challenges due to sample shortages, recent discoveries of additional specimens and samples have created an opportunity for expanded analysis. Future efforts will focus on integrating these new datasets to enhance the understanding of genetic resilience to SSWD. Additionally, whole-genome data will continue to inform studies on genetic diversity, sex-based differences, and population dynamics, and collaborators will process samples from this study for microbiome sequencing.

Thanks in part to this project, genomic research on the sunflower sea star has become a cornerstone of recovery efforts, as highlighted in The Nature Conservancy’s 2022 Roadmap to Recovery.