Relationships between sediment hydrocarbon concentration and salt marsh habitat use in Galveston Bay

Abstract

We sampled nekton, benthic infauna, and sediments in salt marsh habitats at ten locations in upper Galveston Bay, Texas to examine relationships between habitat use and sediment hydrocarbon concentration. Sample locations included marshes heavily oiled in the past as well as areas that were relatively clean. We estimated benthic infaunal densities at each sample site from three pooled 5-cm diameter cores. We also measured salinity, water temperature, dissolved oxygen concentration, water depth, marsh elevation, distance to marsh edge, plant stem density, and turbidity at each site; and sediments at each site were analyzed for grain size, organic content, and petroleum hydrocarbon concentration. Although most marsh sediment samples were contaminated with oil, most samples contained relatively low concentrations of weathered petroleum hydrocarbons. We found potential relationships between animal density and TPH concentration for very few animals. Of 63 abundant taxa (31 nekton and 32 infauna) examined, only six showed a significant negative relationship with sediment TPH levels. As evident from the low R super(2)'s for the models in each case, petroleum hydrocarbon levels in sediment could account for only a small portion of the variability in animal densities for these taxa. In Stepwise Multiple Regression Analyses, hydrocarbon concentration did not contribute significantly to the models for most taxa; and in most cases where TPH or MPH were important variables, the relationship was positive (i.e., animal densities increased with TPH values). The low hydrocarbon concentrations in the sediments of upper Galveston Bay marshes could have contributed to our results either because levels were too low to be toxic or levels were toxic but too low to be detected by most organisms. Our study provides essential baseline data on sediment TPH and animal densities in shoreline marshes of upper Galveston Bay that have a high probability of being impacted by oil spills in the future. The data from our study will be useful in assessing the impact of any future spills in this part of Galveston Bay