Impact of common reed, Phragmites australis, on essential fish habitat:: Influence on reproduction, embryological development, and larval abundance of mummichog (Fundulus heteroclitus)

The invasion of Spartina marshes by the common reed, Phragmites australis, along the east coast of the United States over the last several decades has been well documented, although we know little about the impact of this invasion on the fish fauna and the few published papers seem contradictory. During 1999-2000 (May-September) we evaluated the fish response to vegetation type (Phragmites australis versus Spartina alterniflora) by monitoring several aspects of fish early life history (egg deposition, embryonic development, hatching success, and larval and juvenile abundance) in low salinity marshes in the Mullica River in southern New Jersey. The dominant fish species using the marsh surface, Fundulus heteroclitus (93% of total catch, n = 996 individuals), reproduced in both vegetation types with eggs deposited in leaf axils near the base of the plant in Spartina and in broken stems of Phragmites during both years. These eggs also undergo successful embryonic development to hatching in both vegetation types. Larval and juvenile (5-75 nun total length, but 95% < 34 mm TL) abundance of this species is much reduced on Phragmites-dominated (mean CPUE = 0.02, n = 7 ind) marsh surface relative to Spartina (mean CPUE = 2.31). These findings, and similar results for fish abundance in 1997 and 1998, indicate that the Spartina marsh surface is likely essential fish habitat for this species because it provides habitat for larvae and small juveniles, while Phragmites does not. The Phragmites invasion in brackish marshes may be having deleterious effects on fish populations and possibly on predators that prey upon F. heteroclitus, and as a result, marsh secondary production.