No abstract

-1). This corresponded to a period of high production of suitable food organisms, early stage Calanus finmarchicus, in May 1996 resulting from cooler winter temperatures and late warming after the winter of 1996, suggesting that cooler temperatures favor a prolonged period of food production for larvae and better conditions for growth late in the larval period.

We examined patterns of resource use by size classes of fishes and macroinvertebrates in Barataria Bay, Louisiana. Analyses were based on microhabitat data characterized by water depth, distance from shore, substrate, salinity, dissolved oxygen and temperature. Stratified random samples along the salinity gradient from the nearshore Gulf of Mexico to about 30 km inland were taken monthly with a 1 m beam trawl to characterize distributions of fishes, macroinvertebrates and environmental conditions. From October 1992 through September 1993, 31 602 individuals belonging to 70 species were collected. The 10 most abundant species plus 3 others of special interest were chosen for further analyses. Seasonal differences in environmental variables and differences in resource use among species within ecological groups and within selected species were evaluated by 1-way ANOVAs. A factor analysis resolved 6 environmental variables into 3 orthogonal axes that simplified visualization and comparisons within and among species. Three factors accounted for 70% of the environmental variance and represented seasonality, distance-depth and substrate-salinity axes. Twelve of 13 species showed statistically significant differences between size classes in use of temperature, but some differences were probably due to seasonal temperature changes and the ephemeral nature of life history stages. Within-species differences were less prevalent for variables other than temperature, and the majority were related to use of deeper water as size increased. When seasonal, spatial and size-structured distributions were compared, species with peak abundances during the same seasons had the highest ecological overlaps. Ecological overlaps of 3 closely related species pairs were generally below the mean for the assemblage. Understanding patterns of resource use and the environmental requirements of estuarine-dependent species is an important step in identifying and protecting nursery habitats.

We used a 1‐m beam trawl to characterize microhabitat use by fishes and decapod crustaceans in monthly samples collected in Vermilion and West Cote Blanche bays in central coastal Louisiana. Randomized sampling within strata characterized the distributions of species, size‐classes, and environmental conditions throughout the coastal bays. Microhabitats were characterized by salinity, temperature, dissolved oxygen, depth, distance from shore, substrate type, and turbidity. In 211 short‐duration tows conducted from August 1998 through July 1999, we identified no fewer than 40 fish and 10 decapod crustacean taxa from 22,732 specimens, most of which were juveniles. The five most common species accounted for 67.9% of all individuals and were found in more than one‐half of the samples (≥55.5%). Three of the five species are of immense commercial importance; the other two are important to the ecological community and as forage species for sport and commercial fishes. The two most abundant, Atlantic croakers Micropogonias undulatus and brown shrimp Farfantepenaeus, represented 39.3% of all individuals. A rotated principal components analysis resolved seven environmental variables into three major axes that explained 67% of the environmental variation and were characterized as seasonal (temperature–dissolved oxygen), salinity–turbidity, and depth–distance axes. Separation of species and life history stages in three‐dimensional principal components space reflected temporal and spatial segregation. In univariate analyses of size‐related patterns of microhabitat use within the five common species, 13 of 35 variable comparisons showed evidence of ontogenetic shifts in which at least two size‐class means differed significantly. When resource use patterns were compared without regard to size, significant differences were detected for all seven variables between some species. This suggests that water management that influences important environmental variables (e.g., salinity and temperature) will affect the dominant species and the overall community structure in the system.