Spatial Hysteresis: Non-Recovery of Fish Spatial Distributions with Returning Ocean Condition

In ecology, hysteresis is the phenomenon that an ecological system shifts and remains in a contrasting state regardless of the recovery of external drivers. By extending this phenomenon to the spatial dimension, we define spatial hysteresis as the non-recovery of organismal spatial distribution following the change and return of a spatially heterogeneous environment. Such distributional shifts can alter species interactions and confound the spatial management/conservation areas defined for a species. In this paper, we tested for spatial hysteresis by studying the responses of two groundfish species (American plaice and yellowtail flounder) to spatiotemoral variation in water temperature on the Grand Bank off Newfoundland over a 40-year period. Groundfish distributions and their response to temperature were modeled using a Vector Autoregressive Spatio-Temporal (VAST) model. We detected spatial hysteresis in American plaice but not yellowtail flounder. The distributions of both species contracted and moved southwards during a period when cold-water covered the northern sections of the Grand Bank. Although water temperatures returned to historical levels throughout the Grand Bank after the cold period, only yellowtail flounder re-expanded northwards. These differential responses between species may be due to a variety of effects, including modified meta-population dynamics or modified fish community structure. We call for further studies on the causes and consequences of spatial hysteresis in other ecosystems to advance our knowledge in spatial ecology and benefit the spatial management of natural resources.