We investigated patterns of differential habitat occupation by the crayfish Procambarus alleni, a numerically abundant and trophically important species in freshwater marsh systems of southern Florida. Crayfish were collected from emergent wet prairies and sloughs in marshes forming the headwaters of the St. Johns River, Florida between August 1992 and December 1993. In addition to differences in plant species composition, wet prairies had greater plant biomass and lower water depths than sloughs. Mean density and biomass of crayfish were significantly higher in the densely vegetated wet prairies (28 per m2; 26.9 g per m 2) than in aquatic sloughs (3 per m2; 1.5 g per m2). Crayfish density increased with increasing plant biomass (i.e., habitat complexity) in wet prairies, whereas crayfish density decreased with increasing water levels (i.e., hydroperiod) within slough habitats. Recruitment occurred throughout the study, and the majority of crayfish collected were small in size (< 1.0 g). Ovigerous females were rarely collected and were found only in wet prairies. Differences it+ relative risk of predation, food availability, or a combination of lhese factors are likely generating differences in habitat occupation by the crayfish P. alteni in this wetland habitat mosaic. Efforts to restore and manage freshwater marshes in southern Florida (e.g., Everglades, Lake Okeechobee, Kissimmee River, St. Johns River) would benefit by considering spatial aspects of the ecology of indicator taxa such as crayfish.