Abstract

Sea stars play a pivotal role as keystone predators of inter- and subtidal ecosystems along the west coast of North America.^1,2 Sea Star Wasting Disease (SSWD) is the largest wildlife die-off ever recorded, killing millions of animals in the last three years. The clinical presentation of SSWD varies by species but is most commonly characterized by epidermal lesions, arm autonomy, evisceration, and death.^3,4 It has been observed that the radiographic opacity of commonly affected sea stars such as Pisaster ochraceus and Pycnopodia helianthoides is focally decreased at the site of SSWD lesions on plain film radiographs (M. Murray, pers. comm.). The objectives of this study were to radiographically examine the changes associated with SSWD and determine whether ossicle density is altered in diseased animals. Two groups of sea stars were used for this study (n = 71). The non-clinical group was a collection of P. ochraceus individuals present at Seattle Aquarium (n = 18). The affected group (P. ochraceus) was from nearshore/intertidal coastline of the south Puget Sound. Sea stars of various grades of disease were radiographed using plain-film radiography and computed tomography. Utilizing diagnostic imaging software, the relative average density of the sea star mineral density was measured in Hounsfield units (HU) from CT studies. The average density of selected regions on the sea stars were compared between healthy and SSWD groups. Basic radiographic anatomy for P. ochraceus was established and the radiographs of unaffected and affected animals were compared. Results of the CT studies indicate that ossicle density of clinically-affected P. ochraceus (n = 15) was decreased in comparison to clinically healthy individuals (n = 10). Radiographs revealed anatomic changes between affected and unaffected animals.

Acknowledgements

We would like to thank the following for their assistance: Martin Haulena, the Veterinary Technician Staff and Fish/Invertebrate Husbandry Staff at Vancouver Aquarium; the AQUAVET® Research Fellowship committee and the International Association of Aquatic Animal Medicine (IAAAM) Medway Scholarship committee; the Boeing Company for their ongoing funding of sea star research; and Felicia Nutter and Mauricio Solano at the Cummings School of Veterinary Medicine at Tufts University.

* Presenting author

Literature Cited

1.  Bates AE, Hilton BJ, Harley CD. Effects of temperature, season and locality on wasting disease in the keystone predator sea star Pisaster ochraceus. Diseases of Aquatic Organisms. 2009;86(3):245–251.

2.  Blanchette CA, Richards DV, Engle JM, Broitman BR, Gaines SD. Regime shifts, community change, and population booms of keystone predators at the Channel Islands. In: Proceedings of the California Islands Symposium. 2003;6:435–441.

3.  Eckert GL, Engle JM, Kushner DJ. Sea Star Disease and population declines at the Channel Islands. In: Proceedings of the California Islands Symposium. 1999;5:390–393.

4.  Hewson I, Button JB, Guenkaui BM, Miner B, Newton AL, Gaydos JK, Wynne J, Groves CL, Hendler G, Murray M, Fradkin S, Breitbart M, Fahsbender E, Lafferty KD, Kilpatrick AM, Miner CM, Raimoni P, Lahner L, Friedman CS, Daniels S, Haulena M, Marliave J, Burge CA, Eisenlord ME, Harvell CD. Densovirus associated with sea-star wasting disease and mass mortality. In: Proceedings of the National Academy of Sciences. 2014;111(48):17278–17283.