Nekton use of salt marsh, seagrass, and nonvegetated habitats in a south Texas (USA) estuary

We quantified nekton densities to estimate relative nursery values of Spart ina alterniflora salt marsh, seagrass dominated by Ruppia maritima and Halo dule wrightii, and shallow (<1 m deep) nonvegetated habitat in the Aransas National Wildlife Refuge in Texas. In each of two seasons of high nekton ab undance, fall (September 1993) and spring (May 1994), we took 100 quantitat ive samples using a 1-m(2) drop sampler. We collected a total of 38 species of fishes and 19 species of decapod crustaceans. Vegetated habitats suppor ted significantly higher densities of most numerically dominant species. De nsities of total crustaceans, daggerblade grass shrimp Palaemonetes pugio, blue crabs Callinectes sapidus, and brackish grass shrimp Palaemonetes inte rmedius were significantly higher in salt marsh than seagrass. However, den sities of total fishes, naked gobies Gobiosoma bosc, spotted seatrout Cynos cion nebulosus, pinfish Lagodon rhomboides, gulf pipefish Syngnathus scovel li, brown shrimp Farfantepenaeus aztecus (fall), white shrimp Litopenaeus s etiferus, and pink shrimp Farfantepanaeus duorarum were not significantly d ifferent in salt marsh and seagrass. In spring, brown shrimp densities were higher in seagrass than salt marsh. In contrast to other abundant species, mean densities of bay anchovies Anchoa mitchilli were higher over nonveget ated bottom than in vegetated habitats in both seasons. Nekton size also di ffered among habitats, and organisms generally were smaller in seagrass bed s than in marsh habitat. Our results provide further documentation that sha llow vegetated habitats are important nurseries for many estuarine species. Furthermore, our study showed that where salt marsh and seagrass co-occur, most decapod crustaceans either selected for marsh habitat or showed no pr eference between these two vegetated habitats.