Natural resource conditions at Fort Pulaski National Monument: Findings and management considerations for selected resources

Struthers, Kim

doi:10.36967/2300064

The National Park Service (NPS) Water Resources Division’s Natural Resource Condition Assessment (NRCA) Program initiated an NRCA project with Fort Pulaski National Monument (FOPU) in 2022. The purpose of an NRCA is to synthesize information related to the primary drivers and stressors affecting natural resource conditions at a park and to report conditions for natural resource topics selected by park managers. Resource conditions are evaluated as either a condition assessment or a gap analysis, depending on data availability. For FOPU’s NRCA, managers selected salt marsh, shorebirds, Eastern oyster (Crassostrea virginica), and butterflies as the focal resources. FOPU is comprised of two islands in coastal Georgia, McQueens and Cockspur, which are separated by the Savannah River near its confluence with the Atlantic Ocean. Cockspur Island contains the 19th century masonry fort, Fort Pulaski, and the monument’s visitor services and facilities and is primarily constructed with dredge material from the Savannah River. McQueens Island is almost entirely salt marsh habitat and most of its area is eligible federal wilderness, containing one of Georgia’s oyster recreational harvest areas (RHAs), Oyster Creek RHA. Both McQueens and Cockspur islands are designated as a National Oceanic and Atmospheric Administration Marine Protected Area (MPA), underscoring FOPU’s natural resource significance. Riverine, freshwater, and estuarine wetlands cover 83.81% of FOPU, with the latter accounting for almost 99% of all monument wetlands. Persistently emergent vegetation of smooth cordgrasses (Spartina spp.) and unconsolidated shore represent the dominant wetland types. McQueens Island estuarine wetlands were evaluated for 11 functions and were rated primarily as high functioning, except for the wetland north of Highway 80, where the causeway has altered its ability to function properly. The wetland west of the Highway 80 bend is composed of unconsolidated material so was rated as moderately functioning in carbon sequestration, retention of sediments, and shore stabilization. In contrast, the unconsolidated shore wetland in the Oyster Creek RHA, where the highest concentration of FOPU’s oysters occurs, were rated high for all expected wetland functions. In 2013, over 75% of the total oyster area from within four of Georgia’s RHAs was in the Oyster Creek RHA. A spectral analysis of oyster density in Oyster Creek RHA, comparing 2013 and 2018 images, reported an increase in the high-density class, a decrease in the moderate-low class, and an increase in the no oyster class, with the latter likely a function of how oyster areas were drawn between the images. A successful 2013 enhanced reef project in Oyster Creek RHA reported a pre-enhancement oyster area of 2.68 m2 (28.8 ft2) that increased to 894.2 m2 (0.22 ac) of oysters by 2018. FOPU’s extensive salt marsh habitat and beaches provide critical food sources and habitat for shorebirds in the Atlantic Flyway, especially during the pre-breeding season. The American Oystercatcher (Haematopus palliates), Whimbrel (Numenius phaeopus), and the federally threatened rufa subspecies of Red Knot (Calidris canutus rufa) are identified as high priority species in the flyway and have been observed on Cockspur Island during the Manomet International Shorebird Surveys (2019–2022) at FOPU. The USFWS (2023) is seeking additional critical habitat designation, which will include Cockspur Island, for the rufa subspecies of Red Knot, whose estimated population abundance trend is declining throughout its entire range. FOPU’s non-wetland, upland habitat is primarily located on Cockspur Island and supports vegetation that can serve as host, roost and/or nectar plants for pollinators, especially butterflies. Cedar–Live Oak–Cabbage Palmetto (Juniperus virginiana var. silicicola–Q. virginiana–Sabal palmetto) Marsh Hammock and Cabbage Palmetto Woodland contain the most diversity of beneficial butterfly plants. While a comprehensive butterfly inventory is needed, fall migration surveys have recorded three target species of the Butterflies of the Atlantic Flyway (BAFA): monarch (Danaus plexippus), gulf fritillary (Agraulis vanillae), and cloudless sulphur (Phoebis sennae). Collectively, FOPU’s natural resources are affected by the sea level, which has risen by 0.35 m (1.15 ft) from 1935 to 2022. Hardened shorelines, such as causeways or armored structures, are identified as the greatest threat to the salt marsh habitat’s ability to migrate upland with continued sea level rise. Erosion along Cockspur Island’s north shore is an ongoing issue and FOPU managers have been working with the U.S. Army Corps of Engineers to develop solutions to address the erosion, while also creating habitat for shorebirds. Several agencies routinely monitor for water and sediment pollution in and around FOPU, which, if managed collectively, can inform landscape-level management actions to address drivers that are influencing resource conditions at the ecosystem level.

Natural resource conditions at Fort Pulaski National Monument: Findings and management considerations for selected resources

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