  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.
