Sea Star Wasting Disease in the Keystone Predator Pisaster ochraceus in Oregon: Insights into Differential Population Impacts, Recovery, Predation Rate, and Temperature Effects from Long-Term Research

Abstract

Sea star wasting disease (SSWD) first appeared in Oregon in April 2014, and by June had spread to most of the coast. Although delayed compared to areas to the north and south, SSWD was initially most intense in north and central Oregon and spread southward. Up to 90% of individuals showed signs of disease from June-August 2014. In rocky intertidal habitats, populations of the dominant sea star Pisaster ochraceus were rapidly depleted, with magnitudes of decline in density among sites ranging from -2x to -9x (59 to 84%) and of biomass from -2.6x to -15.8x (60 to 90%) by September 2014. The frequency of symptomatic individuals declined over winter and persisted at a low rate through the spring and summer 2015 (~5–15%, at most sites) and into fall 2015. Disease expression included six symptoms: initially with twisting arms, then deflation and/or lesions, lost arms, losing grip on substrate, and final disintegration. SSWD was disproportionally higher in orange individuals, and higher in tidepools. Although historically P. ochraceus recruitment has been low, from fall 2014 to spring 2015 an unprecedented surge of sea star recruitment occurred at all sites, ranging from ~7x to 300x greater than in 2014. The loss of adult and juvenile individuals in 2014 led to a dramatic decline in predation rate on mussels compared to the previous two decades. A proximate cause of wasting was likely the “Sea Star associated Densovirus” (SSaDV), but the ultimate factors triggering the epidemic, if any, remain unclear. Although warm temperature has been proposed as a possible trigger, SSWD in Oregon populations increased with cool temperatures. Since P. ochraceus is a keystone predator that can strongly influence the biodiversity and community structure of the intertidal community, major community-level responses to the disease are expected. However, predicting the specific impacts and time course of change across west coast meta-communities is difficult, suggesting the need for detailed coast-wide investigation of the effects of this outbreak.

Investigating the Complex Association Between Viral Ecology, Environment, and Northeast Pacific Sea Star Wasting

“…In intertidal communities, localized mass mortality events of Leptasterias hexactis and P. ochraceus were reported from 2010 and 2013 in Horseshoe Cove, CA (Gravem and Morgan, 2017). Mass mortality of P. ochraceus occurred from June to August 2014 and reduced asteroid densities 50-94% amongst sites in Oregon (Menge et al, 2016) and in the San Juan Islands to 25% of their pre-SSWD abundances . The loss of subtidal and intertidal asteroids was correlated with an increase in the abundance of snails (Gravem and Morgan, 2017) and urchins (Schultz et al, 2016), normally prey of asteroids, suggesting that the losses of asteroids after mortality events due to SSWD caused a trophic cascade.…”

“…The loss of subtidal and intertidal asteroids was correlated with an increase in the abundance of snails (Gravem and Morgan, 2017) and urchins (Schultz et al, 2016), normally prey of asteroids, suggesting that the losses of asteroids after mortality events due to SSWD caused a trophic cascade. Strong recruitment of P. ochraceus juveniles on intertidal coastlines indicate that such cascades may be short-lived (Menge et al, 2016). Hence, understanding the mechanisms by which SSWD occur is important for predicting its impact on coastal ecology.…”

Integrating climate change and human impacts into marine spatial planning: A case study of threatened starfish species in Brazil

“…Moreover, ocean warming increases the risk of starfish wasting disease , which is a general description of a set of symptoms that vary slightly among species but generally start with behavioral changes, in cluding lethargy and limb curling, lesions, and end with animal death. This disease has recently devastated starfish species populations along the west coast of North America (Menge et al, 2016;Montecino-Latorre et al, 2016). Global warming-related range shifts of key species are of central importance for the conservation of biodiversity, since changes in the density of starfish species can affect the entire web of interactions, causing serious environmental damage and resulting in biodiversity and economic losses (MMA, 2008).…”

Explaining Ocean Warming: Causes, scale, effects and consequences

“…the 1997 El Niño event: Stokstad (2014)). However, sites in Oregon had cooler water temperatures during recent observations of wasting, making predictions of whether temperature is a driver of the die-offs more difficult to confirm (Menge et al, 2016). Regardless of the ultimate cause of these mortality events, Pisaster ochraceus has long been known to significantly affect the structure and functioning of intertidal communities as an important predator of mussels and other invertebrates.…”

“…The potential mass depletion of these voracious predators would have cascading effects on local ecological communities. It is not yet clear whether new cohorts recently recruited along the Oregon coast (Menge et al, 2016) will be affected or whether they will be able to restore depleted populations and local ecological balance.…”