Indications of hysteresis and early warning signals of reduced community resilience during a Bering Sea cold anomaly

ABSTRACT: The presence of early warning signals (EWS) for regime shifts was tested for in the Bering Sea demersal community during a 2006 to 2013 cold anomaly. During this cold period, community-wide recruitment and distribution patterns failed to reverse responses observed during the previous 2 to 4 decades of warming. These observations are consistent with a model of alternative states—a cold community state and warm community state—separated by hysteresis in the response to temperature. This model predicts that declining resilience of the warm community state during the cold anomaly should have been accompanied by elevated EWS as the system experienced critical slowing down in recovery from stochastic perturbations. This prediction was tested with time series for 3 EWS (temporal autocorrelation, spatial variability, spatial autocorrelation) calculated from distribution data for 12 common fishes and crabs from the Bering Sea trawl survey (1982 to 2015, n = 285 sets yr-1), for a total of 36 taxon × EWS combinations. Fifteen of the 36 time series were significantly elevated during the cold anomaly (community-wide randomization test, p < 0.0001). Comparison with a ‘control’ group of 3 cold years outside of the cold anomaly failed to replicate observations of elevated EWS, suggesting that the EWS signal was due to the persistent perturbation of the cold anomaly rather than temperature effects on the distribution and behavior of study animals per se. These results suggest that theoretical predictions for EWS may be supported in large ecosystems such as the Bering Sea.