THE IMPORTANCE OF EDGE FOR NATANT MACROFAUNA IN A CREATED SALT-MARSH

The relationship between marsh edge and animal use was examined in a planted Spartina alterniflora marsh located in the Galveston Bay system of Texas. A completely randomized block experimental design was used with each of four blocks containing a control and experimental sector. Marsh edge was increased through the construction of channels in experimental sectors. Channel construction had no detectable effect on marsh surface elevation. Effects of these simulated tidal creeks on habitat use were examined by sampling nekton at high tide with,drop enclosures both on the marsh surface and within the channels. Crustaceans dominated the nekton, and use of the marsh surface in experimental sectors was significantly higher than in controls; densities of brown shrimp Penaeus aztecus, white shrimp P. setiferus, and daggerblade grass shrimp Palaemonetes pugio were 4.6 to 13 times higher near the channels. Polychaete densities in marsh sediments were also significantly higher near channels, and densities of decapod predators were positively correlated with densities of these infaunal prey. Thus, channel effects on natant decapods may have been related to the distribution of prey organisms. However, increased densities of natant fauna along the channel edge may simply reflect a requirement for departure from the marsh surface at low tide. Marsh-surface densities of small bait fishes,bay anchovy Anchoa mitchilli and the inland silverside Menidia beryllina, also increased near channels, but highest densities of these fishes were in the creeks themselves. The abundance and distribution of juvenile blue crabs Callinectes sapidus and gulf marsh fiddler crabs Uca longisignalis were not affected by the addition of experimental channels. Overall, the study results indicate that habitat value of created salt marshes can be enhanced by incorporating tidal creeks into the marsh design.