Nekton of New Seagrass Habitats Colonizing a Subsided Salt Marsh in Galveston Bay, Texas

Subsidence and erosion of intertidal salt marsh at Galveston Island State Park, Texas, created new areas of subtidal habitat that were colonized by seagrasses beginning in 1999. We quantified and compared habitat characteristics and nekton densities in monospecific beds of stargrass Halophila engelmanni and shoalgrass Halodule wrightii as well as adjacent nonvegetated substrates. We collected 10 replicates per habitat type during April, July, October, and December 2001. Most habitat characteristics varied with season. Water temperature, salinity, and dissolved oxygen were similar among habitat types. Turbidity and depth were greatest in H. engelmanni beds and least in H. wrightii beds. H. engelmanni exhibited shorter leaves and higher shoot density and biomass core super(-1) than H. wrightii. Densities of almost all dominant species of nekton (fishes and decapods) were seasonally variable, all were higher in seagrass habitats than in nonvegetated habitats, and most were higher in one seagrass species than the other. Naked goby Gobiosoma bosc, code goby Gobiosoma robustum, bigclaw snapping shrimp Alpheus heterochaelis, and blue crab Callinectes sapidus were most abundant in H. engelmanni. Brown shrimp Farfantepenaeus aztecus, brackish grass shrimp Palaemonetes intermedius, and daggerblade grass shrimp Palaemonetes pugio were most abundant in H. wrightii. Pinfish Lagodon rhomboides and pink shrimp Farfantepenaeus duorarum were equally abundant in either seagrass. Most dominant nekton varied in size by month, but only two (L. rhomboides and C. sapidus) exhibited habitat-related differences in size. Nekton densities in these new seagrass habitats equaled or exceeded densities associated with historical and current intertidal smooth cordgrass Spartina alterniflora marsh. Continued seagrass expansion and persistence should ensure ecosystem productivity in spite of habitat change.