NMFS NUMBER: 96-NER-027
The Role of Tidal Salt Marsh as Essential Habitat in Production
of Juvenile Weakfish (Cynoscion regalis)
Michael P. Weinstein, Sam C. Wainright, and Kenneth W.
National Marine Fisheries Service, Northeast Region, One
Blackburn Drive, Gloucester, MA 01930. TELEPHONE:
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.