Blue crab abundance patterns in shallow bay and salt-marsh habitats of the Texas Gulf coast

Previous studies of blue crab (Callinectes sapidus) use of salt-marsh have occurred almost exclusively in young, Spartina-dominated marshes or peripheral S. alterniflora fringe.  We examined size-specific abundance patterns of blue crabs in shallow habitats of the Guadalupe Estuary, Texas, where salt-marsh was mature and dominated by high-marsh halophytes.  During October 2004-March 2006, we collected monthly crab samples in shallow bay adjacent to salt-marsh and the edges and open water of connected and isolated interior-marsh ponds.  Ponds comprised fewer but larger crabs than bay habitat.  Mean crab density was ten times greater in bay (9.5 ± 1.0 crabs/m) than pond (0.5-1.0 crabs/m) habitats, but mean biomass was comparable across habitats (2.4-3.3 g/m).  Size-distributions were highly right-skewed in all habitats but most skewed in shallow bay, where crabs were typically < 10 mm in carapace-width.  Crabs contributing greatest to biomass were smallest (11-30 mm) in bay habitat, larger (31-80 mm) along pond edges, and largest (111-130 mm) in pond open water.  The best predictors of density for crabs ≤ 30 mm were micro-site characteristics (habitat, water column structure, structural complexity).  Findings suggest shallow bay provided nursery habitat for young blue crabs but interior-marsh ponds were important for dispersing juvenile and adult crabs.