The Role of Tidal Salt Marsh as Essential Fish....
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GRANT NUMBER:  NA86FD0109           NMFS NUMBER:  96-NER-027

REPORT TITLE:  The Role of Tidal Salt Marsh as Essential Habitat in Production of Juvenile Weakfish (Cynoscion regalis)

AUTHOR:  Michael P. Weinstein, Sam C. Wainright, and Kenneth W. Able

PUBLISH DATE:  February 15, 2000

AVAILABLE FROM:  National Marine Fisheries Service, Northeast Region, One Blackburn Drive, Gloucester, MA 01930.  TELEPHONE:  (978) 281-9267


Stable isotope ratios of carbon, nitrogen, and sulfur in weakfish (Cynoscion regalis), bay anchovy (Anchoa mitchilli), and white perch (Morone americana) from Delaware Bay were a function of the relative position of the marsh restoration trajectory.  With one exception, weakfish captured in different zones of the open bay displayed significant differences in their isotope composition.  Fish captured in the upper bay had isotope signatures characteristic of Phragmites australis-dominated marshes, and weakfish from the lower bay had greater similarities to Spartina alterniflora-dominated marshes.   Weakfish collected in mid-bay were intermediate in their stable isotope composition.  Benthic microalgae also contributed to weakfish nutrition in the open bay.  Fish collected in tidal creeks--Mad Horse Creek in mid-bay and Dennis Creek in the lower bay--did not differ significantly from each other, nor did they differ from fish captured in the corresponding open-water zone.  White perch and bay anchovy collected in polyhaline restoration and reference (Moore's Beach) sites also had stable isotope signatures that reflected contributions from both benthic microalgae and Spartina alterniflora.  Isotope values from white perch captured at the reference site were slightly enriched compared to the restoration sites.  At mid-estuary, oligo-mesohaline locations, Phragmites australis contributed to the isotopic composition of both white perch and bay anchovy.  Although P. australis was not dominant at the reference marsh (Mad Horse Creek), it seemed to influence the flow of nutrients into all three species.  White perch were not collected in open waters of Delaware Bay, but weakfish and bay anchovy were abundant at offshore sampling stations.   A striking result of this study was the widespread occurrence of stable isotopes that originated in macrophytes and benthic microalgae of salt marshes in weakfish and bay anchovy collected several kilometers from shore.  This also was true of weakfish "staging" at the bay mouth just prior to their offshore emigration.   Interestingly, fish from Mad Horse Creek (a reference marsh where Phragmites were abundant only along creek banks) were intermediate at their isotopic composition.   Although benthic microalgal signature varied both within and among sites, the isotopic composition of weakfish bay anchovy and white perch were clearly influenced by these primary producers across all marsh types.

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