Growth, survival, and metal content of marsh invertebrates fed diets of detritus from Spartina alterniflora Loisel. and Phragmites australis Cav. Trin. ex Steud. from metal-contaminated and clean sites

Marsh vegetation plays an important role in trophic ecology of estuaries. Once broken down to detritus, it is an important food source for many organisms. In Atlantic Coast marshes, the reed Phragmites australis has been invading many areas once dominated by smooth cordgrass, Spartina alterniflora. In this study we evaluated the growth of and trophic transfer of metals to estuarine invertebrates when fed diets of detritus from these different plant species. Decaying leaves from populations of Phragmites, natural Spartina, and restored Spartina from both the Hackensack Meadowlands, New Jersey, and the more pristine Accabonac Harbor of East Hampton, New York, were collected from the marsh surface in the spring. Decaying leaves were pureed and fed to the fiddler crabs Uca pugnax and U. pugilator, and to the grass shrimp Palaemonetes pugio. In fiddler crabs we monitored limb regeneration, molting and weight. U. pugilator regenerated limbs and molted equally well on all six diets. Most of the U. pugnax arrested growth midway through regeneration on all 6 diets. A repeat experiment with smaller crabs, which did complete the process, found no consistent differences among the six diets and control food, although control food and Phragmites detritus had higher N concentrations than the Spartina detritus. Grass shrimp fed all six diets did not survive beyond 3 weeks. In another experiment using HM sediments from each vegetation type (containing detritus, meiofauna, and microflora), survival was equally high among treatments and the shrimp fed sediments from the restored Spartina site or control food grew better than those fed sediments from the Phragmites or natural Spartina sites. Although metal concentrations in detritus varied between sites and plant species, the crabs of each group did not differ in metal concentrations after the feeding experiment. Our data do not support the general assumption that Phragmites leaf detritus is of poorer nutritional quality than Spartina alterniflora leaf detritus to estuarine consumers.