Sea star wasting: A tale of red herrings, misleading results and a newly recognized marine disease etiology

Dr. Ian Hewson

Associate Professor, Cornell University

Abstract

Sea star wasting (SSW) mass mortality was observed from 2013 – 2014 affecting over 20 species from the Gulf of Alaska to Baja California, and resulted in substantial population decline of affected taxa. The etiology of SSW is unresolved. SSW was initially ascribed to a candidate pathogen (the sea star associated densovirus) and elevated temperature. However, both are inconsistently related to the condition across the entire affected geographic range. Tissue-associated microbiomes compared between the appearance of body wall lesions and prior to wasting in experimental incubations revealed an increase in relative abundance of strict and facultative anaerobes, along with copiotrophic taxa that elsewhere degrade primary producer-derived dissolved organic matter. Based on this observation, SSW was hypothesized to be an organismal response to suboxic conditions at the animal-water interface (i.e. the diffusive boundary layer). Organic matter enrichment experiments, experimental manipulations of dissolved oxygen conditions, time-series analyses at a field site, imaging studies to infer DBL extent, and retrospective stable isotopic analyses of samples from 2013-2014, provided evidence for the key role of microorganisms inhabiting the animal-water interface in SSW. Together these convergent lines of evidence suggest that SSW is an environmental stress response, driven by microorganisms not intimately associated with tissues. Furthermore, this work emphasizes that large-scale marine diseases, even those which appear density dependent or transmissible in water, may be non-infectious in nature.