Microhabitat Use by Macroinvertebrates in Barataria Bay, Louisiana

A drop sampler was used to collect macroinvertebrates along transects in open and closed marshes within the Barataria Basin. Three-hundred-seventy-seven samples, covering 448 m2, were collected between August 1988 and September 1989. Sampling focused along the marsh edge where open water and flooded Spartina meet, covering a broad range of environmental conditions including different stem densities, distances to the marsh edge, and water depths. Other variables measured included water temperature, velocity, dissolved oxygen, salinity, turbidity, substrate, and marsh vegetation. Of the ten most frequently-occurring macroinvertebrates, three were transients (Callinectes sapidus, C. similis, and Penaeus aztecus), and seven were residents (Mysidopsis spp., Palaemonetes spp., Clibanarius vittatus, Eurypanopeus depressus, Ampilesca vadorum, Gammarus mucronatus, and Neanthes succinea). A size-frequency analysis showed that most seasonal abundance peaks were recruitment peaks. P. aztecus, G. mucronatus, N. succinea, and Mysidopsis showed spring recruitment. C. sapidus and E. depressus showed summer, and C. similis showed fall recruitment peaks. Palaemonetes and A.vadorum showed winter recruitment. C.vittatus showed two peaks, winter and summer. Factor analysis described three well-defined axes that explained 52.3% of the variance. These were seasonal (temperature and dissolved oxygen), microspatial (depth, distance, and stem density), and macrospatial (salinity). In univariate analyses, differential patterns of microhabitat use were significant among several species. Among residents, Palaemonetes was different from Mysidopsis in temperature, depth, and stem density. Among the transients, Penaeus aztecus and the two Callinectes species differed in temperature, and the Callinectes species differed in stem density, salinity, and turbidity. There were generally more differences among transients than among residents. A tethering experiment was also conducted to examine differential day and night survival rates in the marsh edge. This was a preliminary examination of predation as an explanation for microhabitat selection. Aside from some confounding factors, analyses showed that some daytime survival rates were significantly lower