Terracing at Pierce Marsh in Galveston Bay 2001-2002

Marsh terracing is used to restore coastal wetlands by converting shallow nonvegetated bottom to intertidal marsh. Terraces are constructed from excavated bottom sediments, and are commonly arranged in a checkerboard pattern of square cells with open corners to form terrace fields. The project was located in shallow estuarine waters, and used bottom sediments or upland soils to construct intertidal areas planted with smooth cordgrass, Spartina alterniflora. We used a quantitative sampling device to compare nekton densities and biomass in habitat types of marsh terraces of three cell sizes at Pierce Marsh in Galveston Bay to a nearby reference marsh. Within terrace cells, density, biomass, and species richness were generally higher in marsh vegetation than over nonvegetated bottom. We also used Geographic Information System (GIS) and high-resolution aerial photography to classify areas into land (marsh vegetation) and water and applied fishery density models to assess fishery support. These models describe finescale distribution patterns for brown shrimp Farfantepenaeus aztecus, white shrimp Litopenaeus setiferus, and blue crab Callinectes sapidus across shallow estuarine habitat types (emergent marsh and shallow open water) of Galveston Bay. We show that populations of most fishery species increase as cell size decreases. However, as cell size decreases, the cost of terrace construction increases much faster than population size. Therefore, terrace fields constructed of medium or large cells would be more cost effective in providing fishery habitat than would terraces composed of small cells. Based on our modeling results, restored sites supported relatively high populations of fishery species compared to pre-restoration conditions. However, restoration sites did not support populations’ equivalent to a reference marsh system. Restoration projects should maximize the area of marsh vegetation and create a high degree of water-marsh interspersion to provide the most benefit for fishery species.