Nekton use of marsh-surface habitats in Louisiana (USA) deltaic salt marshes undergoing submergence

We used lift nets from April through November 1991 in Louisiana (USA) deltaic marshes to compare nekton densities in 3 marsh-surface habitats undergoing submergence and having different surface elevations (Distichlis spicata marsh = high elevation; intact Spartina alterniflora marsh = intermediate elevation; and hummocky S. alterniflora marsh = low elevation). Daggerblade grass shrimp Palaemonetes pugio, gulf killifish Fundulus grandis, sheepshead minnow Cyprinodon variegatus, diamond killifish Adinia xenica, striped mullet Mugil cephalus, blue crab Callinectes sapidus, brown shrimp Penaeus aztecus, and white shrimp P. setiferus numerically dominated samples from all 3 marsh types and accounted for 93% of the total catch. These dominant species exhibited 3 distinct patterns of spatial distribution among habitats. Gulf killifish and diamond killifish were most abundant on D. spicata marsh, whereas high densities of brown shrimp and white shrimp were found on hummocky S. alterniflora marsh. Densities of daggerblade grass shrimp, sheepshead minnows, striped mullet, and blue crabs were similar among the 3 marsh types. Although in an advanced state of deteriorarion, hummocky S. alterniflora marsh did not lose its habitat function. Submergence of coastal Gulf of Mexico marshes may benefit marsh nekton, especially penaeid shrimp, by increasing the percentage of time the marsh surface is available for use. However, these benefits will be short-lived in regions where rapid submergence leads to a significant decrease in total marsh habitat.