Spatiotemporal Modeling of Nursery Habitat Using Bayesian Inference: Environmental Drivers of Juvenile Blue Crab Abundance
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Nursery grounds are favorable for growth and survival of juvenile fish and crustaceans through abundant food resources and refugia, and enhance secondary production of populations. While small-scale studies remain important tools to assess nursery value of habitats, targeted applications that unify survey data over large spatiotemporal scales are vital to generalize inference of nursery function, identify highly productive regions, and inform management strategies. Using 21 years of GIS and spatiotemporally indexed field survey data on potential nursery habitats, we constructed five Bayesian models with varying spatiotemporal dependence structures to infer nursery habitat value for juveniles of the blue crab C. sapidus within three tributaries in lower Chesapeake Bay. Out-of-sample predictions of juvenile counts from a fully nonseparable spatiotemporal model outperformed predictions from simpler models. Salt marsh surface area, turbidity, and their interaction showed the strongest associations (and positively) with abundance. Relative seagrass area, previously emphasized as the most valuable nursery in small spatial-scale studies, was not associated with abundance. Hence, we argue that salt marshes should be considered a key nursery habitat for blue crabs, even amidst extensive seagrass beds. Moreover, identification of nurseries should be based on investigations at broad spatiotemporal scales incorporating multiple potential nursery habitats, and on rigorously addressing spatiotemporal dependence.
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