Abstract
Disturbances such as disease can reshape communities through interruption of ecological interactions. Changes to population demographics alter how effectively a species performs its ecological role. While a population may recover in density, this may not translate to recovery of ecological function. In 2013, a sea star wasting syndrome outbreak caused mass mortality of the keystone predator Pisaster ochraceus on the North American Pacific coast. We analyzed sea star counts, biomass, size distributions, and recruitment from long‐term intertidal monitoring sites from San Diego to Alaska to assess regional trends in sea star recovery following the outbreak. Recruitment, an indicator of population recovery, has been spatially patchy and varied within and among regions of the coast. Despite sea star counts approaching predisease numbers, sea star biomass, a measure of predation potential on the mussel Mytilus californianus, has remained low. This indicates that post‐outbreak populations have not regained their full predation pressure. The regional variability in percent of recovering sites suggested differences in factors promoting sea star recovery between regions but did not show consistent patterns in postoutbreak recruitment on a coast‐wide scale. These results shape predictions of where changes in community composition are likely to occur in years following the disease outbreak and provide insight into how populations of keystone species resume their ecological roles following mortality‐inducing disturbances.
Highlights
Disturbance and mass mortalities can reshape the ability of affected populations to maintain their role within an ecosystem
Experimental sea star removals in many locations on the Pacific coast have demonstrated that when P. ochraceus abundances are severely reduced for a sufficiently long duration, M. californianus increase in percent cover (Paine, 1966, 1974; Robles et al, 2009)
While recruitment pulses occurred in some locations during the peak of the outbreak, it is possible that large numbers of those recruits died before reaching maturity due to juveniles’ high sea star wasting syndrome (SSWS) mortality
Summary
Disturbance and mass mortalities can reshape the ability of affected populations to maintain their role within an ecosystem. This means that even when a population recovers to the same predisturbance number of individuals, it will not entirely resume its ecological role until more individuals reach adult size and restore predisturbance size structure (Bellwood, Hoey, & Hughes, 2012; Hamilton & Caselle, 2015) This is true for species functioning as keystone predators, which play a large role in maintaining community composition relative to their abundance (Paine, 1966). Experimental sea star removals in many locations on the Pacific coast have demonstrated that when P. ochraceus abundances are severely reduced for a sufficiently long duration, M. californianus increase in percent cover (Paine, 1966, 1974; Robles et al, 2009) This expansion of the mussel bed decreases the number of other species on the primary substrate, while it creates more habitat for infaunal and epibiont species (Lafferty & Suchanek, 2016; Suchanek, 1986). We discuss the importance of recruitment and postsettlement mortality as potential contributors to the differential recovery patterns that we observed
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