Mechanisms of marsh habitat alteration due to phragmites:: Response of young-of-the-year Mummichog (Fundulus heteroclitus) to treatment for Phragmites removal

In recent decades, marshes naturally dominated by Spartina spp. have been replaced by Phragmites australis throughout the northeastern United States. We suggest that early in this invasion there was little effect on the fish fauna. As the invasion proceeds, the marsh surface habitat became more altered (i.e., elevated, flattened, reduced water-fined depressions, and reduced standing water), which resulted in a reduction of feeding, reproduction, and nursery function for fishes, especially Fundulus spp. These potential changes in marsh habitat and function have resulted in numerous attempts to remove Phragmites and restore Spartina spp. To evaluate the response of marsh surface fishes to Phragmites treatment, we examined fish use in the brackish water reaches of Alloway Creek in the Delaware Bay estuary. Reference Phragmites habitats were compared with reference Spartina alterniflora-dominated habitats and sites treated (1996-1998) to remove Phragmites to restore former vegetation (i.e., restored, now comprised of 100% Spartina). Fish were sampled with an array (n = 9 at each site) of shallow pit traps (rectangular glass dishes, 27.5 x 17.5 x 3.7 cm). Small individuals (mean = 17.5, 5-45 rnm TL) dominated all pit trap collections. Fish abundance was highest at the restored (catch per unit effort [CPUE] = 2.16) and Spartina (CPUE = 0.81) sites with significantly lower values at Phragmites (CPUE = 0.05) habitats. Samples were dominated by young-of-the-year mummichog, Fundulus heteroditus (98% of total fish, n = 631). The only other fish species collected was spotfin killifish, Fundulus luciae (2% of total catch, n = 14), which was only present in restored and Spartina habitats. These observations suggest that the restored marsh is providing habitat (water-filled depressions on the marsh surface) for young-of-the-year Fundulus spp. These marshes are responding favorably to the restoration based on the much greater abundance of fish in restored versus Phragmites habitats and the overall similarity between restored and Spartina habitats.