Spatiotemporal Modeling of Nursery Habitat Using Bayesian Inference: Environmental Drivers of Juvenile Blue Crab Abundance

Abstract

Nursery grounds provide conditions 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 structured habitats and environmental factors, targeted applications that unify survey data over large spatial and temporal scales are vital to generalize inference of nursery function, identify highly productive regions, and inform management strategies. Using 21 years of spatio-temporally indexed survey data (i.e., water chemistry, turbidity, blue crab, and predator abundance) and GIS information on potential nursery habitats (i.e., seagrass, salt marsh, and unvegetated shallow bottom), we constructed five Bayesian hierarchical models with varying spatial and temporal dependence structures to infer variation in nursery habitat value for young juveniles (20–40 mm carapace width) of the blue crab Callinectes sapidus within three tributaries (James, York and Rappahannock Rivers) in lower Chesapeake Bay. Out-of-sample predictions of juvenile blue crab counts from a model considering fully nonseparable spatiotemporal dependence outperformed predictions from simpler models. Salt marsh surface area and turbidity were the strongest determinants of crab abundance (positive association in both cases). Highest crab abundances occurred near the turbidity maximum where relative salt marsh area was greatest. Relative seagrass area, which has been emphasized as the most valuable nursery in studies conducted at small spatial scales, was not associated with high crab abundance within the three tributaries. Hence, salt marshes should be considered a key nursery habitat for the blue crab, even where extensive seagrass beds occur. The patterns between juvenile blue crab abundance and environmental variables also indicated that identification of nurseries should be based on investigations at broad spatial and temporal scales incorporating multiple potential nursery habitats, and based on statistical analyses that address spatial and temporal statistical dependence.

Assessment of Treatment-Specific Tethering Survival Bias for the Juvenile blue crabCallinectes Sapidusin a Simulated Salt Marsh

“…In concert with evidence of high abundance and growth of juvenile blue crabs in salt marshes (e.g. Thomas, Zimmerman and Minello, 1990; Fitz and Wiegert, 1991; Zimmerman, Minello and Rozas, 2002; Lipcius et al, 2005; Seitz, Lipcius and Seebo, 2005; Johnson and Eggleston, 2010; Isdell et al, 2021; zu Ermgassen et al, 2021; Hyman et al, 2022), our findings on survival support the conclusion that structurally complex S. alterniflora habitats enhance survival rates and promote high abundance of small juvenile blue crabs.…”

“…Taken together with earlier studies reporting no treatment-specific tethering bias among seagrass meadows and unstructured sand habitats (Pile et al, 1996; Hovel and Lipcius, 2001), our findings expand the portfolio of habitats under which tethering may be reliably employed with respect to juvenile blue crabs. A benefit of the present study is that results presented here retroactively support past research that did not test for the presence of treatment-specific bias in salt marshes (Hyman et al, 2022; Shakeri et al, 2020).…”

“…Previous studies estimating survival in post-recruitment juveniles have primarily focused on seagrass meadows, algae and unstructured sand habitats to infer nursery status (Pile et al, 1996; Hovel and Lipcius, 2001, 2002; Lipcius et al, 2005; Johnston and Lipcius, 2012; Bromilow and Lipcius, 2017). However, mounting evidence suggests that alternative habitats such as salt marshes serve as highly productive nurseries (Johnson and Eggleston, 2010; Hyman et al, 2022, 2023). While past experiments have not found treatment-specific interactions among unstructured sand and seagrass meadows (Hovel and Lipcius, 2001, 2002; Pile et al, 1996), such interactions have not been quantified in salt marsh nurseries (Shakeri et al, 2020).…”

Beautiful swimmers attack at low tide

“…The blue-crab fishery contributes (US)$100s of millions of dollars to the United States economy. My observations underscore how vital salt marshes are to this fishery (Baker et al, 2020;Hyman et al, 2022). To better estimate just how vital they are to the blue-crab fishery, future studies should consider stable isotope analysis combined with gut content analysis of blue crabs and population estimates in salt marshes at high and low tides.…”

“…The blue crab seems to have solved this problem with a feeding strategy that allows for 24-h feeding. This suggests that salt marshes are more important to their production than previously thought (Hyman et al, 2022;Lipcius et al, 2005). The blue-crab fishery contributes (US)$100s of millions of dollars to the United States economy.…”