Contrasting patterns of habitat use by prawns and crayfish in a headwater marsh of the St. Johns River, Florida

We compared seasonal patterns of habitat use by the prawn Palaemonetes palu dosus and the crayfish Procambarus alleni in Blue Cypress Marsh Conservatio n Area, Florida. Prawn densities were similar to those found in other oligo trophic wetlands of southern Florida, whereas crayfish densities were much greater than reported previously for other wetlands in the area. Prawns and crayfish had strikingly different patterns of habitat use. Prawn density a nd biomass were similar in wet prairies and sloughs, whereas crayfish densi ty and biomass were significantly higher in wet prairies. Within habitats, the abundance of prawns and crayfish generally increased with increasing st ructural complexity and the abundance of crayfish generally decreased with increasing water depth. Differences in risk of predation, frequency of agon istic encounters, food availability, and other factors likely contributed t o observed patterns of habitat use. Because of differences in their ability to burrow and avoid concentration into dry-season refugia, prawns and cray fish responded very differently to seasonal variation in hydrologic conditi ons. Prawn densities were initially low (following a severe drought) and th en increased during much of the study period, whereas crayfish densities we re relatively stable throughout the study period. Overall, it appears that prawns are more responsive to antecedent hydrologic conditions and crayfish are more responsive to the availability of suitable habitats such as wet p rairies.