Sea Star Wasting

Prior to October 2013, there were thousands of large sunflower stars, Pycnopodia helianthoides, at this site near Defence Island in Howe Sound. On April 3 2017, only six small individuals were found. (Photo: Neil McDaniel)

Starting in the spring of 2013, a widespread sea star mass mortality event spread up and down the west coast of North America in what might be the largest wildlife die-off event in recorded history. At least 20 species are affected, with trickle-down ecological effects at multiple levels of the food web. Despite progress in understanding the causes and consequences of the outbreak, many mysteries remain, and sea star wasting syndrome is ongoing.

The current status of sea stars varies widely by species and location. Although there are anecdotal reports of recovery, the frequency of sea star sightings continues to decline for many species, and signs of wasting persist. At the same time, sea star distribution is increasingly patchy and abundance is quite variable (Figure 1).

Figure 1. Between 2009 and 2017, the sighting frequency (i.e., the proportion of dive surveys where sea stars were recorded) of four common sea star species in the Strait of Georgia declined, but the average abundance for all sites surveyed in the Strait of Georgia (as estimated visually using roving dive surveys) was variable. Represented species include: sunflower stars (Pycnopodia helianthoides), purple stars (Pisaster ochraceus), leather stars (Dermasterias imbricata) and mottled stars (Evasterias troschelii). Data source: Pacific Marine Life Surveys Database of opportunistic SCUBA-based observations, accessed 15 Aug 2017.

Interestingly, there was an unusual boom in the abundance of juvenile sea stars of several species in 2014 and 2015. Juvenile sunflower stars, in particular, were extremely abundant at several locations in the Strait of Georgia, Puget Sound and elsewhere. Similarly, juvenile mottled stars (Evasterias troschelii) formed ultra-dense aggregations at some sites for a short period of time (see banner photo). Unfortunately the abundance was short-lived; the juveniles disappeared over a period of weeks to months, and no evidence of their abundance has so far been reflected in adult populations.

Research into the pathology (characterization), etiology (causes and origins), epidemiology (distribution and contributing factors), and ecology of the disease are ongoing at several institutions across North America. In British Columbia, monitoring efforts are ongoing at the Hakai Institute, Simon Fraser University, the University of B.C., the Coastal Ocean Research Institute, and elsewhere. A Sea Star Wasting Disease Task Force, coordinated by researchers at Oregon State University and the University of California, recently formed to develop a coordinated research strategy, consider mitigation and recovery approaches, and develop new legislation to improve disease response and management. Ongoing concern about the status of sunflower stars has led to initiatives to have sunflower stars assessed for listing under Canada’s Species at Risk Act.

Sea star wasting continues to serve as a stark indicator of how much there is to learn about the complexity of ocean systems. Further research into the disease will help forward our understanding about wildlife mortality events, and how human actions and management might prevent or mitigate similar outbreaks in the future.

The leather star, Dermasterias imbricata (right), is a generalist opportunistic feeder, but it was unusual to see one eating the remains of a velcro star, Stylasterias forreri (left), that appeared to have died due to sea star wasting disease. (Photo: Neil McDaniel)