Factors affecting restoration of Halodule wrightii to Galveston Bay, Texas

Abstract

Experimental restoration of Halodule wrightii (shoalgrass) to its former range on Galveston Island, texas, began in April 1994. We tested the effects of site, planting density, water depth, and fertilizer addition on survival and growth through June 1996. Temperature, salinity, light transmittance, turbidity, and sediment properties at two restoration sites, Redfish Cover and Snake Island Cove, were similar to those in naturally occurring grassbeds in nearby Christmas Bay. Halodule survival, coverage, and new shoot densities were affected by site (significantly higher at Redfish Cover than at Snake Island Cover, which eventually failed), by planting density (significantly higher when planted on 0.25-m or 0.5-m centers rather than on 1.0-m centers), and by water depth (significantly higher when planted in relatively shallow water). Propagation (spreading from transplant units) was significantly greater from 0.25-m or 0.5-m center planting but was not consistently affected by site or water depth. Fertilizer enhanced propagation but not survival. After two years, Redfish Cover produced belowground biomass similar to that observed in Christmas Bay, but aboveground biomass remained significantly less. Snake Island Cove plant mortality in September 1995 may have been presaged by low root-rhizome carbohydrate levels observed in October 1994, but causes remain unknown. Further restoration of Halodule to Galveston Bay is possible at selected sites, but structural equivalency will take longer than two growing seasons to achieve.