Patterns of resource use by fishes and macroinvertebrates in Barataria Bay, Louisiana

Abstract

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.