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Philip Caldwell, Geoffrey Matthews, and Thomas Minello
The value of coastal wetlands for fishery resources in the northern Gulf of Mexico is highly dependent on the small-scale spatial configuration of these habitats. The amount of fragmentation and marsh-water edge is positively related to the abundance and productivity of juvenile brown shrimp, white shrimp, blue crabs, spotted seatrout, and red drum. Unfragmented marsh systems, those without open water, ponds, and creeks, are less productive. Available map products do not provide information at an appropriate spatial resolution to identify the fragmentation and relative complexity of wetlands or the amount of marsh edge habitat, and thus, are unable to provide the relative habitat value of wetlands for fishery species. This proposed effort will use currently available coastal imagery to map marsh edge vegetation and will determine the relative value of coastal wetlands for fishery species.
DOQQ of regularly flooded salt marsh.
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Marsh vegetation and water are classified in the aerial image (DOQQ's).
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1-m distance grids used in population density estimation
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This is a new initiative that is based on NMFS research documenting the value of marsh edge habitats for fishery resources. Over one half of the coastal wetlands in the United States are found in the northern Gulf of Mexico. Access to the marsh surface is a critical factor determining the value of these wetlands for important fishery species such as penaeid shrimps, blue crabs, and many fishes, and a recent summary of 16 years of research on habitat use in estuaries of Texas and Louisiana has documented the value of marsh edge habitats for these species. Much of the productivity of coastal wetlands is derived from the marsh vegetation found immediately adjacent (within about 5 m) to open water, ponds, and creeks. Available map products of coastal wetlands such as the USGS National Wetland Inventory (NWI) or NOAA's Coastal Change Analysis Program (C-CAP) initiative do not provide information at an appropriate spatial scale to identify this valuable habitat characteristic. We have used ArcView's Image Analyst and Spatial Analyst extensions along with readily available digital images (Digital Ortho Quarter Quads from USGS) at 1 m resolution to classify selected coastal marshes in Galveston Bay, Texas into shallow open water, marsh edge, and inner marsh habitats. In one DOQQ, and area of about 500 hectares of salt marsh was composed of 37% shallow open water, 34% marsh edge (0-5 m from open water), and 29% inner marsh. We are extending this approach to map the NWI polygons for regularly flooded emergent estuarine vegetation in the Galveston Bay area.
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