Habitat-specific differences in mercury concentrations of Mississippi grass shrimp from Caddo Lake, Texas

Total and methylmercury concentrations were measured in Mississippi grass shrimp (Palaemonetes kadiakensis) that were collected from river, wetland, and open-water habitats in Caddo Lake, Texas. Because grass shrimp are short-lived and relatively immobile, their mercury concentrations are representative of the mercury levels at the location from which they are collected. The highest concentrations of mercury are in grass shrimp collected from the river and the lowest were from open-water habitats. Mercury levels in shrimp collected in the wetland are intermediate between river and open-water habitats but exhibit a large amount of variation suggesting the wetlands of Caddo Lake are quite heterogeneous and require further study to understand their spatial variation. Methylmercury is strongly correlated to total mercury and constitutes 94% of the total mercury regardless of the habitat from which they were collected. This suggests total mercury concentrations are a useful proxy for predicting methylmercury concentrations.