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 Spartina alterniflora salt marsh, seagrass dominated by Ruppia maritima and Halodule wrightii, and shallow (<1 m deep) nonvegetated habitat in the Aransas National Wildlife Refuge in Texas. In each of two seasons of high nekton abundance, fall (September 1993) and spring (May 1994), we took 100 quantitative 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 supported significantly higher densities of most numerically dominant species. Densities of total crustaceans, daggerblade grass shrimp Palaemonetes pugio, blue crabs Callinectes sapidus, and brackish grass shrimp Palaemonetes intermedius were significantly higher in salt marsh than seagrass. However, densities of total fishes, naked gobies Gobiosoma bosc, spotted seatrout Cynoscion nebulosus, pinfish Lagodon rhomboides, gulf pipefish Syngnathus scovelli, brown shrimp Farfantepenaeus aztecus (fall), white shrimp Litopenaeus setiferus, and pink shrimp Farfantepanaeus duorarum were not significantly different 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 nonvegetated bottom than in vegetated habitats in both seasons. Nekton size also differed among habitats, and organisms generally were smaller in seagrass beds than in marsh habitat. Our results provide further documentation that shallow 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 preference between these two vegetated habitats.