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Award Detail

Doing Business As Name:Cornell University
  • Ian Hewson
  • (607) 255-0151
Award Date:08/17/2015
Estimated Total Award Amount: $ 564,562
Funds Obligated to Date: $ 564,562
  • FY 2015=$564,562
Start Date:08/15/2015
End Date:07/31/2020
Transaction Type:Grant
Awarding Agency Code:4900
Funding Agency Code:4900
CFDA Number:47.050
Primary Program Source:040100 NSF RESEARCH & RELATED ACTIVIT
Award Title or Description:Microbial ecology of sea star wasting disease
Federal Award ID Number:1537111
DUNS ID:872612445
Parent DUNS ID:002254837
Program Officer:
  • Michael Sieracki
  • (703) 292-7585

Awardee Location

Street:373 Pine Tree Road
Awardee Cong. District:23

Primary Place of Performance

Organization Name:Cornell University
Street:373 Pine Tree Rd
Cong. District:23

Abstract at Time of Award

Beginning in June 2013 and continuing to present (May 2015), over 20 species of sea stars (Asteroidea, Echinodermata) have been affected by sea star wasting disease (SSWD), affecting populations from central Alaska to Baja California. The disease has lead to greatly reduced abundance or disappearance of these keystone predators, which may result in profound alteration to benthic community structure. Recent work has identified the sea star associated densovirus (SSaDV) as the most likely causative agent of the disease. SSaDV is related to densoviruses inhabiting other echinoderms worldwide, and has been present in West Coast asteroid populations for at least 72 years. Hence, there remain significant knowledge gaps in our understanding of how SSaDV actually elicits SSWD symptoms, especially how the echinoderm host, densovirus and microbiome constituents interact. This project will address three major questions: 1) does viral infection change the composition of the sea star microbiome?, 2) what is the variation of viral genomes and their associated virulence?, and 3) does larval dispersal spread the disease between habitats? This project will address these hypotheses through time-course measurements of host, pathogen and associated microorganisms, genome-genome comparisons between historical and contemporary viral strains, and through experiments targeting larvae and juvenile asteroids in aquaria and in nature. This work will support training of a graduate student (recruitment targeting an under-represented minority) and several undergraduates in biological oceanographic and disease ecology techniques. Information will be disseminated through public outreach activities at two high-profile Pacific coast public aquariums (the Seattle and Vancouver Aquariums), through a website dedicated to the project, and through public talks and media exposure. This project will address three fundamental questions relating to Sea Star Wasting Disease (SSWD): 1) How does SSaDV causes SSWD symptoms and how does the disease progress from primary infection through animal mortality; 2) How do current genotypes of SSaDV vary from those present historically, and is virulence related to genome polymorphisms; and 3) Are larvae and juvenile asteroids differentially affected by SSaDV, and are broadcast-spawned bipinarria a viable mechanism for SSaDV dispersal between distant habitats. The first question will be addressed by experimental inoculation of naïve sea stars with SSaDV, then time-course monitoring of host transcription (i.e. transcriptomics via RNAseq), microbiome composition via 16S rRNA sequencing and quantitative PCR, and viral load and prevalence using quantitatice PCR. The second question will be addressed by amplifying the entire genome of SSaDV and related densoviruses, then perform genome-genome comparisons to identify polymorphic DNA in key protein-encoding regions. The third question will be addressed by collecting bipinarria from plankton at field locations adjacent to spawning asteroid populations, and by performing time-course observations of captive juvenile sea stars and monitoring their bacterial and viral loads using quantitative PCR. This work will be performed primarily in the Salish Sea region, with SSaDV - naïve asteroids collected from Alaskan waters.

Publications Produced as a Result of this Research

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Elliot Jackson, Kalia Bistolas, Jason Button, Chaunte Lewis and Ian Hewson "Novel circular single-stranded DNA viruses among an asteroid, echinoid and holothurian (Phylum: Echinodermata)" PLoS One, v., 2016, p.. doi: 

Hewson, I., Sullivan, B., Jackson, E.W., Xu, Q., Long, H., Lin, C., Quijano Cardé, E.M., Seymour, J., Siboni, N., Jones, M.R.L., and Sewell, M.A. "Perspective: Something Old, Something New? Review of Wasting and Other Mortality in Asteroidea (Echinodermata)" Frontiers in Marine Science, v.6, 2019, p.. doi: 

Jackson, E. W. Bistolas, K. S. Button, J. B. Hewson, I. "Novel Circular Single-Stranded DNA Viruses among an Asteroid, Echinoid and Holothurian (Phylum: Echinodermata)" PLoS One, v., 2016, p.. doi:e0166093 

Hewson, I. Bistolas, K.S.I. Quijano Carde, E.M. Button, J.B. Foster, P.J. Flanzenbaum, J.M. Kocian, J. Lewis, C. K. "Investigating the complex association between viral ecology, environment and Northeast Pacific Sea Star Wasting" Frontiers in Marine Science, v., 2018, p.. doi: 

Hewson, I, Bistolas, KSI, Quijano Cardé, EM, Button JB, Foster PJ, Flanzenbaum JM, Kocian J, Lewis CK "Investigating the complex association between viral ecology, environment and North Pacific sea star wasting" Frontiers in Marine Science, v.5, 2018, p.77.

Jackson, E.W., Pepe-Ranney, C., Johnson, M.R., Stein, D., Distel, D.L., & Hewson, I. "A highly prevalent and persistent densovirus discovered among sea stars from the Atlantic Coast of the United States." Applied and Environmental Microbiology, v.86, 2020, p.. doi:10.1128/AEM.02723-19 

Jackson, E. W. Pepe-Ranney, C. Debenport, S. J. Buckley, D. H. Hewson, I. "The Microbial Landscape of Sea Stars and the Anatomical and Interspecies Variability of Their Microbiome" Frontiers in Microbiology, v.9, 2018, p.12.

Hewson,Ian Sullivan,Brooke Jackson,Elliot W. Xu,Qiang Long,Hao Lin,Chenggang Quijano Cardé,Eva Marie Seymour,Justin Siboni,Nachshon Jones,Matthew R. L. Sewell,Mary A. "Perspective: Something Old, Something New? Review of Wasting and Other Mortality in Asteroidea (Echinodermata)" Frontiers in Marine Science, v.6, 2019, p.. doi: 

Hewson I. "Technical pitfalls that bias comparative microbial community analyses of aquatic disease" Diseases of Aquatic Organisms, v.137, 2019, p.109.

Mordecai, G.J. Hewson, I. "Coronaviruses in the Sea" Frontiers in Microbiology, v., 2020, p.. doi:doi: 10.3389/fmicb.2020.01795 

Project Outcomes Report


This Project Outcomes Report for the General Public is displayed verbatim as submitted by the Principal Investigator (PI) for this award. Any opinions, findings, and conclusions or recommendations expressed in this Report are those of the PI and do not necessarily reflect the views of the National Science Foundation; NSF has not approved or endorsed its content.

Intellectual Merit

"Sea star wasting disease" describes a suite of abnormal symptoms that have affected starfish since at least 1898 and led to their widespread disappearance from coastlines. In 2013 ? 2014, millions on starfish from Alaska to Baja California were afflicted by this condition and since that time some species, including the Sunflower Star, have almost disappeared from some places (e.g. the Salish Sea) entirely. The cause of sea star wasting disease was initially believed to be a virus called the Sea Star associated Densovirus (SSaDV). We hypothesized that sea star wasting disease resulted in changes in the starfish microbiome, starting with infection by this virus, followed by induction of starfish self-destruction (called apoptosis) and ending with the rapid growth of bacteria that decompose the dying animals. Work very early in this project failed to confirm a connection between this virus and sea star wasting, so we instead searched again for possible causes of the condition. This project found that sea star wasting is a consequence of a complex interaction between microorganisms (primarily bacteria) living near the animals surface and phytoplankton-derived material. Starfish are surrounded by a layer of relatively stagnant water that is rich in nutrients. Because bacteria thrive on these nutrients, this layer generally contains a much larger number of these organism than surrounding waters. When these bacteria consume nutrients, they deplete oxygen within this layer. These bacteria also readily consume nutrients provided by algae, so when there is a lot of phytoplankton around, these bacteria thrive and drive the layer above animals to become suboxic. Starfish breathe through their skin. Hence, when this layer becomes suboxic they cannot breathe as well, and so many deleterious processes are triggered, including a form of self-destruction known as apoptosis. Ultimately, through this project, we have linked the occurrence of sea star wasting disease to the timing of algal blooms, their proximity to decomposing carcasses of adjacent starfish afflicted by the disease, and warmer water conditions (which further reduce oxygen availability). We showed this phenomenon to occur during experiments where we depleted available oxygen in aquaria, where we added sugars and other analogs of algal exudates, and by looking at the types of bacteria that occur prior to, at the time of, and after the animals start to show sea star wasting disease signs. Furthermore, we found a significant relationship between the surface roughness ? which dictates the width of this layer ? and the extent of sea star wasting disease in natural populations. Finally, we looked at elemental signatures of starfish from 2013 ? 2014 and found strong evidence that animals that died from sea star wasting had tissues enriched with an isotope that indicated the prevalence of anaerobic conditions. Hence, we rejected our initial hypothesis (that viral infection triggered apoptosis and bacteria proliferated on the dying animal) and accepted the alternate hypothesis that phytoplankton stimulated bacteria, which led to suboxic conditions that triggered apoptosis. Furthermore, we found that numerous viruses became very abundant after wasting began, so it is likely that our initial observation of SSaDV associated with sea star wasting was wrong because it is a symptom, not cause, of the condition.

The finding that sea star wasting disease is likely not caused by a microorganism (i.e. it is not transmissible or pathogenic), but may relate to the density of organisms within a population, has important consequences for biological oceanography. For example, other organisms that breathe through their skin (including sponges and corals) may face challenges in the future through this phenomenon.

Broader Impacts

This project trained two graduate students, seven undergraduate researchers, and a high school student, including 4 under-represented minority students. The project results have been communicated to the public through engagement with popular media outlets, through public talks at museums, and through the PIs website/blog. In addition, we have engaged the public through several social media accounts to report significant findings. All 12 publications to date have been published in open-access peer-reviewed scientific journals, and data has been deposited at publically available databases.

Last Modified: 09/01/2020
Modified by: Ian Hewson

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