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PIs: Lawrence P. Rozas, Thomas J. Minello,
Roger J. Zimmerman, and Philip Caldwell
We used data from 1,984 samples taken
approximately monthly over eleven years
(1982-1992) with a 2.6-m2 drop sampler to
quantify and compare nekton densities in
Spartina alterniflora marsh edge and
over adjacent shallow non-vegetated bottom (SNB)
within a cove of the Galveston Bay estuary.
We also used a Geographic Information System
(GIS), aerial photography, and population
models to track changes in wetland area and
trends in fishery populations over time.
Decapod crustaceans were less speciose than
fishes (35 vs. 60 species) in our samples,
but this taxonomic group accounted for most
(91%) of the animals we collected. Most
species peaked in abundance during either
spring or fall, and were absent or occurred
in low densities during winter. Inter-annual
variability in animal abundance was high,
and most species were taken in greatest
densities either in 1982 and 1983 or from
1989-1991. Mean densities of all abundant
decapod crustaceans and half of the most
abundant fishes in our study were
significantly greater in marsh vegetation
than over SNB. Based on our GIS analysis, we
estimated that 61% of the wetlands in the
study area were converted to open water
between 1982 and 1995; marsh edge (marsh
within 1m of the shoreline) was reduced by
70% during the same period.
Our fishery models showed that brown shrimp,
Farfantepenaeus aztecus, white
shrimp, Litopenaeus setiferus, and
blue crab, Callinectes sapidus
populations also declined substantially
during this period as the area of wetlands
and marsh edge was reduced. A
marsh-terracing project in 1999 replaced
some open water with marsh, and our models
show that populations of these fishery
species rebounded in response to this recent
restoration effort. Publication:
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