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1. Elevated temperature linked to signs associated with sea star wasting disease in a keystone European species, Asterias rubens

   https://doi.org/10.3354/meps14451  

   Smith, S; Kunc, HP; Hewson, I; Collins, PC (December 2023, Marine Ecology Progress Series)

   Sea star wasting disease (SSWD) refers to a suite of gross signs affecting Asteroidea species. These include epidermal lesions, everted viscera, arm autotomy, and ultimately, full body disintegration leading to mortality. The common sea starAsterias rubensis a keystone species in the coastal Northeast Atlantic and may be susceptible to the disease. While the precise aetiology of SSWD remains poorly understood, environmental instability, including rising sea temperatures, has been linked to SSWD outbreaks. To investigate this connection, an experiment was conducted to quantify disease sign expression inA. rubensunder elevated temperature. We exposed sea stars to either elevated temperature (18°C) or a control treatment (12°C) for a 14 d period. We quantified the presence of disease signs associated with SSWD, the progression of signs, and survival of individuals. Elevated temperature induced a greater number of signs consistent with SSWD and also resulted in mortality for some of those animals. Furthermore, larger individuals were more likely to show increased signs of disease. Our results provide evidence that signs associated with SSWD increase with elevated temperature. 

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2. Large-scale impacts of sea star wasting disease (SSWD) on intertidal sea stars and implications for recovery

   https://doi.org/https://www.doi.org/10.1371/journal.pone.0192870  

   C. Melissa Miner1*, Jennifer L. (March 2018, PloS one)

   Disease outbreaks can have substantial impacts on wild populations, but the often patchy or anecdotal evidence of these impacts impedes our ability to understand outbreak dynamics. Recently however, a severe disease outbreak occurred in a group of very well-studied organisms±sea stars along the west coast of North America. We analyzed nearly two decades of data from a coordinated monitoring effort at 88 sites ranging from southern British Columbia to San Diego, California along with 2 sites near Sitka, Alaska to better understand the effects of sea star wasting disease (SSWD) on the keystone intertidal predator, Pisaster ochraceus. Quantitative surveys revealed unprecedented declines of P. ochraceus in 2014 and 2015 across nearly the entire geographic range of the species. The intensity of the impact of SSWD was not uniform across the affected area, with proportionally greater population declines in the southern regions relative to the north. The degree of population decline was unrelated to pre-outbreak P. ochraceus density, although these factors have been linked in other well-documented disease events. While elevated seawater temperatures were not broadly linked to the initial emergence of SSWD, anomalously high seawater temperatures in 2014 and 2015 might have exacerbated the disease's impact. Both before and after the onset of the SSWD outbreak, we documented higher recruitment of P. ochraceus in the north than in the south, and while some juveniles are surviving (as evidenced by transition of recruitment pulses to larger size classes), post-SSWD survivorship is lower than during pre-SSWD periods. In hindsight, our data suggest that the SSWD event defied prediction based on two factors found to be important in other marine disease events, sea water temperature and population density, and illustrate the importance of surveillance of natural populations as one element of an integrated approach to marine disease ecology. Low levels of SSWD-symptomatic sea stars are still present throughout the impacted range, thus the outlook for population recovery is uncertain. 

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3. Lessons Learned from the Sea Star Wasting Disease Investigation

   https://doi.org/10.1146/annurev-marine-040623-082617  

   Hewson, Ian; Johnson, Mitchell R; Reyes-Chavez, Brandon (June 2024, Annual Review of Marine Science)

   Marine invertebrate mass mortality events (MMEs) threaten biodiversity and have the potential to catastrophically alter ecosystem structure. A proximal question around acute MMEs is their etiologies and/or environmental drivers. Establishing a robust cause of mortality is challenging in marine habitats due to the complexity of the interactions among species and the free dispersal of microorganisms from surrounding waters to metazoan microbiomes. The 2013–2014 sea star wasting disease (SSWD) MME in the northeast Pacific Ocean highlights the difficulty in establishing responsible agents. In less than a year of scientific investigation, investigators identified a candidate agent and provided at the time convincing data of pathogenic and transmissible disease. However, later investigation failed to support the initial results, and critical retrospective analyses of experimental procedures and reinterpretation of early findings disbanded any candidate agent. Despite the circuitous path that the investigation and understanding of SSWD have taken, lessons learned from the initial investigation—improving on approaches that led to misinterpretation—have been successfully applied to the 2022Diadema antillaruminvestigation. In this review, we outline the history of the initial SSWD investigation, examine how early exploration led to spurious interpretations, summarize the lessons learned, provide recommendations for future work in other systems, and examine potential links between the SSWD event and theDiadema antillarumMME. 

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4. Virome Variation during Sea Star Wasting Disease Progression in Pisaster ochraceus (Asteroidea, Echinodermata)

   https://doi.org/10.3390/v12111332  

   Hewson, Ian; Aquino, Citlalli A.; DeRito, Christopher M. (November 2020, Viruses)

   null (Ed.)

   Sea star wasting disease (SSWD) is a condition that has affected asteroids for over 120 years, yet mechanistic understanding of this wasting etiology remains elusive. We investigated temporal virome variation in two Pisaster ochraceus specimens that wasted in the absence of external stimuli and two specimens that did not experience SSWD for the duration of our study, and compared viromes of wasting lesion margin tissues to both artificial scar margins and grossly normal tissues over time. Global assembly of all SSWD-affected tissue libraries resulted in 24 viral genome fragments represented in >1 library. Genome fragments mostly matched densoviruses and picornaviruses with fewer matching nodaviruses, and a sobemovirus. Picornavirus-like and densovirus-like genome fragments were most similar to viral genomes recovered in metagenomic study of other marine invertebrates. Read recruitment revealed only two picornavirus-like genome fragments that recruited from only SSWD-affected specimens, but neither was unique to wasting lesions. Wasting lesion margin reads recruited to a greater number of viral genotypes (i.e., richness) than did either scar tissue and grossly normal tissue reads. Taken together, these data suggest that no single viral genome fragment was associated with SSWD. Rather, wasting lesion margins may generally support viral proliferation. 

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5. Two decades of change in sea star abundance at a subtidal site in Puget Sound, Washington

   https://doi.org/10.1371/journal.pone.0286384  

   Casendino, Helen R.; McElroy, Katherine N.; Sorel, Mark H.; Quinn, Thomas P.; Wood, Chelsea L. (June 2023, PLOS ONE)

   Thuesen, Erik V. (Ed.)

   Long-term datasets can reveal otherwise undetectable ecological trends, illuminating the historical context of contemporary ecosystem states. We used two decades (1997–2019) of scientific trawling data from a subtidal, benthic site in Puget Sound, Washington, USA to test for gradual trends and sudden shifts in total sea star abundance across 11 species. We specifically assessed whether this community responded to the sea star wasting disease (SSWD) epizootic, which began in 2013. We sampled at depths of 10, 25, 50 and 70 m near Port Madison, WA, and obtained long-term water temperature data. To account for species-level differences in SSWD susceptibility, we divided our sea star abundance data into two categories, depending on the extent to which the species is susceptible to SSWD, then conducted parallel analyses for high-susceptibility and moderate-susceptibility species. The abundance of high-susceptibility sea stars declined in 2014 across depths. In contrast, the abundance of moderate-susceptibility species trended downward throughout the years at the deepest depths– 50 and 70 m–and suddenly declined in 2006 across depths. Water temperature was positively correlated with the abundance of moderate-susceptibility species, and uncorrelated with high-susceptibility sea star abundance. The reported emergence of SSWD in Washington State in the summer of 2014 provides a plausible explanation for the subsequent decline in abundance of high-susceptibility species. However, no long-term stressors or mortality events affecting sea stars were reported in Washington State prior to these years, leaving the declines we observed in moderate-susceptibility species preceding the 2013–2015 SSWD epizootic unexplained. These results suggest that the subtidal sea star community in Port Madison is dynamic, and emphasizes the value of long-term datasets for evaluating patterns of change. 

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