The distribution, abundance, and potential prey of a marsh resident fish:
Phragmites australis versus Spartina alterniflora
Diana L. Raichel, Fish and Wildlife Biologist, U.S. Fish and Wildlife Service, New Jersey Field Office, Pleasantville, NJ, Diana_Raichel@fws.gov
The invasive plant Phragmites australis characterizes the Hackensack Meadowlands landscape, largely due to a long history of ecological disturbance. Given the current and planned restorations in the Meadowlands to replace this plant with the native salt marsh grass Spartina alterniflora, information regarding fish response to these vegetation types is particularly relevant. However, this information is presently limited and contradictory. This study, conducted at Mill Creek in Secaucus, compares Phragmites-dominated marsh and Spartina-dominated marsh as habitat for the various life history stages of the resident marsh fish the common mummichog. These fish are integral to the transfer of energy from the marsh surface to adjacent subtidal waters and thus estuarine food webs. The objectives of this two-year study (1999 and 2000) were to 1) compare the distribution and abundance of the eggs, larvae, juveniles and adults of mummichog and their invertebrate prey inhabiting Spartina-dominated marshes with Phragmites-dominated marshes, and 2) experimentally investigate the influence of marsh surface microtopography on larval fish abundance within Phragmites-dominated marshes. In 2000, we verified that egg deposition does occur in Phragmites-dominated marshes. However, for both years, the abundance of larval/small juveniles (4 - 20 mm) in Spartina was significantly greater than in Phragmites-dominated marshes, while larger juveniles and adults (>20 mm) were similarly abundant in both habitat types. The overall abundance of larvae/small juveniles was significantly greater in experimental Phragmites plots in which microtopography was manipulated to resemble that of Spartina marshes, than in Phragmites control plots. Major groups of invertebrate taxa differed between marsh types, with potential larval fish prey significantly more abundant in Spartina marshes. Based on these findings, Phragmites-dominated marshes may not provide suitable habitat for the early life history stages of resident fishes such as the mummichog. The low abundance of larvae and small juveniles in Phragmites marshes is probably due to inadequate larval habitat and perhaps decreased prey availability for these early life history stages.