Southern flounder Paralichthys lethostigma populations in Texas have been in steady decline over the last 25 years.Despite the economic importance of this species, little is known about their juvenile    habitat requirements.The goal of this study was to determine temporal and spatial habitat use patterns    for juvenile southern flounder and characterize these patterns in terms of habitat selection.Monthly sampling was conducted over a two-year recruitment period (January-April 2004, and January-March 2005) in the Aransas-Copano estuaries on the Texas coast.  The bay complex was divided into three zones based on a decreasing salinity gradient and increasing distances from Aransas Pass.  Replicate estuarine habitat types were sampled in each of these zones.  Triplicate samples were taken using a beam trawl in different habitats, seagrass (Halodule wrightii), marsh (Spartina alterniflora), and open-water (nonvegetated bottom), at each of nine sampling sites within each zone. Catch data indicated distinct habitat distribution patterns.  Highest densities    occurred closest to Aransas Pass in vegetated, sandy bottom areas.  Lowest densities occurred in    nonvegetated, muddy bottom areas farthest from the pass.  Habitat selection patterns for southern  flounder were examined using experimental mesocosms.  Since wild fish occurred at low densities,  hatchery-reared fish were used.Four common natural habitat types were simulated in twelve 38-L  glass tanks: (1) oyster reef, (2) salt marsh (Spartina alterniflora) (3) seagrass (Halodule wrightii),  and (4) nonvegetated, sand bottom.  Mesocosms were divided in half with each containing a different    constructed habitat type.  Selection patterns were compared for all possible combinations of habitat    pairings.  Habitat selection experiments showed juvenile southern flounder selected nonvegetated sand    bottom over structured habitat (vegetated and oyster habitats) and selected seagrass over all other    structured habitats when nonvegetated sand bottom was not available for selection.  Habitat use    patterns show vegetated habitats near a tidal inlet serve as important nursery grounds for juvenile    southern flounder.  Habitat selection experiments indicated juvenile flounder select to settle in nonvegetated sand bottom habitats near or in vegetated areas. A 25-year bag seine data set from Texas Parks and Wildlife Department (TPWD) was analyzed to assess long-term spatial and temporal  patterns.  Bag seine data were interpreted using Arc GIS 9.1 to calculate southern flounder catch per    hectare (catch per unit effort) during the peak recruitment period (December-April).  Data maps    showed high numbers of flounder near tidal inlets, with the highest number of flounder collected during   April.  These observations were similar to field observations and support the importance of vegetated habitats near tidal passes as nursery areas.