The Largest Epidemic Observed in Marine Animals

As the earth warms from human carbon emissions, sea temperatures are rising. Evidence suggests that changes in the global climate could be causing more frequent disease outbreaks in the marine environment. Sea star wasting disease (SSWD) is a disease effecting seas stars and sea urchins sporadically and causing mass mortality events.

Fun Fact: Sea stars can live to be 35 years old!

History

In 2014 and 2015 a major decline in populations of the sea star Pisaster ochraceus were observed along the west coast of North America. Pisaster ochraceus often called the purple sea star or ochre stars range from Prince William Sound Alaska, USA to Cedros Island, Baja California, Mexico. While outbreaks of SSWD have been occurring since the 1970’s, this was the worst occurrence that affected over 20 species and spread from Alaska to Mexico. Scientists have claimed it was the largest epidemic to be observed in wild marine animals. Imagine a SCUBA diver going from seeing dozens of sea stars to none in only a couple of years. While the disease is naturally occurring, it is theorized that increased water temperatures in 2014 exacerbated the disease’s impact. As you may recall from my previous blogs this month, sea stars are keystone species and a major loss such as this would (and has) result in a negative ripple through the entire ecosystem.

Disease

As I have mentioned the cause of this disease is natural and scientists do not fully understand what causes it. “Wasting” refers to a slow degradation of tissue however, this disease can progress rapidly killing sea stars in only a few days. The disease starts off by causing a twisted or deflated appearance to the sea star. Next, lesions develop on the surface of the sea star and the tissue begins to degrade around these lesions. Furthermore, the body may fragment and then dissolve, resulting in death for the sea star. These symptoms are similar to other stressors a sea star may undergo such as when a sea star is trapped too high in the intertidal zone. This similarity makes it difficult for experts to diagnose a SSWD outbreak early on.

Impacts and Future

SSWD continues to persist at low levels and continues to kill off sea stars. Historical data and further data collection are essential in creating a ‘benchmark’ based on normal or pre-diseased population conditions like abundance and distribution. Further research can aid in understanding what causes major outbreaks and how to better predict future outbreaks using models. Recovery for sea star populations involves the recruitment of individuals, juvenile survival to adulthood and disease persistence. These recovery components can vary among the affected populations and thus having a benchmark can help monitor sea stars and make informed assessments of recovery at multiple scales. This ministration could help to identify the factors that might enable or hinder the recovery of affected populations.

How Can You Help?

You can submit personal observations of diseased sea stars to researchers at the University of California Santa Cruz here. Observations from the public can help scientists document the distribution of individuals and monitor the health of sea stars. Also, check out the sea star map to better understand the distribution and current concentration of SSWD. This map was created by UCSC and contains recent SSWD geographical data. Finally, taking action to reduce your carbon footprint by using energy wisely, eating sustainably and being politically active by voting can help to fight climate change.

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References

Miner CM, Burnaford JL, Ambrose RF, Antrim L, Bohlmann H, Blanchette CA, et al. (2018) Large-scale impacts of sea star wasting disease (SSWD) on intertidal sea stars and implications for recovery. PLoS ONE 13(3): e0192870. https://doi.org/10.1371/journal.pone.0192870