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MEPS prepress abstract   -  DOI: https://doi.org/10.3354/meps13227

Testing ecological release as a compensating mechanism for mass mortality in a keystone predator

Jenna Sullivan-Stack*, Bruce A. Menge

*Corresponding author:

ABSTRACT: Top predator decline has been ubiquitous across systems, and predicting changes in resultant community dynamics is a major challenge for ecologists and managers. Ecological release predicts that loss of a limiting factor, such as a dominant competitor or predator, can release a species from control, thus allowing increases in its size, density and/or distribution. The 2014 sea star wasting syndrome (SSWS) outbreak decimated populations of the keystone predator Pisaster ochraceus along the Oregon coast. This event provided an opportunity to test the predictions of ecological release across a broad spatial scale and determine the role of competitive dynamics in top predator recovery. We hypothesized that after Pisaster loss, populations of the subordinate sea star Leptasterias sp. would grow larger, more abundant, and move downshore. We based these predictions on prior research in Washington State showing that Leptasterias competed with Pisaster for food. Further, we predicted that ecological release of Leptasterias could provide a bottleneck to Pisaster recovery. Using field surveys, we found no clear change in density or distribution in Leptasterias populations post-SSWS, and decreases in body size. In a field experiment, we found no evidence of competition between similar-sized Leptasterias and Pisaster. Thus, the mechanisms underlying our predictions were not in effect along the Oregon coast as they were in Washington, a finding we attribute to differences in habitat overlap and food availability between the 2 regions. Our results suggest that response to the loss of a dominant competitor can be unpredictable even when based in theory and previous research.