Responses of resident marsh fishes to stages of Phragmites australis invasion in three mid Atlantic estuaries

Modification of brackish marshes by nonindigenous Phragmites australis has occurred across a broad geographical area in eastern North America. Among its effects on marsh processes, Phragmites may be increasingly unfavorable to marsh surface fishes as its invasion progresses within an estuary. We assessed the effect of the Phragmites invasion on resident marsh surface fishes by examining the population response of Fundulus heteroditus (mununichog, 5-48 mm TL) and F. luciae (spotfin killifish, 5-41 mm TL) to four distinct invasion stages in three estuaries of the U.S. mid Atlantic region (New Jersey, Delaware, and Maryland). We documented precipitous declines in mean catch per unit effort of F. heteroditus in pit traps from natural marsh (51.6), through initial (33.8), early (12.3), and late invasion stages (2.4) across all sites. A similar pattern was documented for F. luciae, with mean catch per unit effort in pit traps declining from natural marsh (48.9), through initial (39.1), early (9.3), and late invasion stages (2.7). Population structure of both species also changed somewhat across invasion stages such that we collected a narrower size range of individuals of both species from late invasion stages. Patterns suggest that as the Phragmites invasion progresses, there is a decline in habitat function for larval and juvenile F. heteroditus and an increased risk of extirpation of F. luciae from brackish marshes along the east coast of the U.S.