Ontogenetic Patterns in Juvenile Blue Crab density: Effects of Habitat and Turbidity in a Chesapeake Bay Tributary

Abstract

Nursery habitats are characterized by favorable conditions for juveniles, such as higher food availability and lower predation risk, and dispropor-tionately contribute more individuals per unit area to adult segments of the population compared to other habitats. However, nursery habitat inference is complicated by changes in habitat preferences with ontogeny; individuals in early-life stages frequently inhabit different habitats than older juveniles or adults. In this mensurative field experiment, we modeled the density of two juvenile blue crab, Callinectes sapidus, size classes based on carapace width (CW) across multiple habitats at various locations within an estuarine seascape during the blue crab recruitment season. We examined four habi-tat types--unstructured sand, seagrass meadows, salt marsh edge (SME), and shallow detrital habitat (SDH). Results indicated that densities of small ju-venile blue crabs ([≤]15 mm CW) were highest in seagrass, whereas densities of larger juveniles (16-30 mm CW) were highest in SME. Densities of large juveniles in SME were also greater than those of small juveniles, suggest-ing possible secondary dispersal to SME by small juveniles after settlement and recruitment in seagrass. Turbidity was positively correlated with densi-ties of both size classes, although our model did not address whether this was due to top-down (refuge) or bottom-up (food availability) mechanisms. Ob-served patterns in size-specific habitat utilization may result from changing requirements of juvenile blue crabs with size, as animals minimize mortality-to-growth ratios. Taken together with previous work and patterns observed in SME, these findings emphasize the role of salt marsh habitat within juve-nile blue crab ontogeny and underscore the need to quantify and preserve the complete chain of habitats used by juveniles.