American Oystercatcher Habitat Loss in the Big Bend
The Big Bend is home to Florida’s largest concentration of nesting American oystercatchers in Florida. Because the region has no barrier islands or large shell and marsh rakes, the breeding habitat for oystercatchers here is different and more limited than along the Atlantic and other parts of the Gulf coast. Currently, the greatest threat to nesting birds in the area is habitat degradation and loss. Overwash has been the largest known contributor to nest loss in the region since 2011 and habitat loss has been directly observed.
For example, biologists documented a historically productive breeding site, Derrick Key, erode and disappear over ten years. To better understand the factors limiting nesting success in this area, the Florida Fish and Wildlife Conservation Commission and the University of Florida set out to quantify breeding habitat loss in the region and lay the foundation for high-priority habitat restoration to benefit American oystercatchers.
Derrick Key Erosion between 2007 to 2017. Photo on left includes an American oystercatcher nest in the lower right corner (taken by Pat Leary).
Two breeding areas along the Nature Coast were the focus of the study – The Cross Florida Barge Canal spoil islands in Citrus County and small islands around Cedar Key in Levy County. The Barge Canal spoil islands consist of a chain of 10 islands that were artificially created in the late 1960s. In contrast, Cedar Key islands consist of seven naturally occurring islands. The Barge Canal islands are a mix of limestone and shell. Shell derived from oyster reefs and offshore shoals line the small offshore islands around Cedar Key. Due to the karst nature of this region, there is no significant sediment transport suitable for beach development or maintenance.
Using aerial images from the past 40 years, island size and changes in the shoreline of the nesting islands in the two study areas were analyzed. Results showed that oystercatcher nesting habitat in both study areas has declined. In both areas, erosion is the primary factor contributing to habitat loss.
Despite being constructed mostly of limestone rock, the Barge Canal spoil islands have slowly eroded over time losing 55% of the total area between 1979 and 2017. Several of the smallest islands have completely eroded away since they were created.
Significant erosion of the Cedar Key islands was also observed and happened much faster. Between 1974 and 2016 the total area decreased by 39%. Additionally, the two most important nesting islands in Cedar Key showed the greatest habitat loss. Derrick Key disappeared and Gomez Key is rapidly losing area and elevation. In addition to the islands getting smaller, many of the islands have become highly susceptible to overwash events.
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Photo on left is an American oystercatcher pair on a nest at Gomez Key. The photo on the right shows the pair at the nest site during an overwash event.
Recent studies on oysters in the Big Bend offer an answer to this sudden increase in erosion. Researchers documented a 66% loss of the extent of oyster reefs in the area over 30 years. Oyster reefs provide many important services to the Big Bend coastal ecosystem, including shoreline stabilization and protection from wave energy. When the oyster reefs disappear, this service is lost and the areas they previously protected are subject to increased erosion. In Cedar Key, 85% of the erosion occurred after 1995. The timing of oystercatcher habitat loss closely follows that of the oyster reef declines, indicating the two are connected.
Gomez Key erosion between 1982 and 2017.
The results of this study indicate that all nesting habitat in the study area is decreasing. Oystercatchers are long-lived, extremely faithful to nesting sites and there are no additional potential nesting habitats in the area, so birds continue to use the nesting habitat that remains. Because the habitat is decreasing and what remains is poor quality, these islands may be acting as an ecological trap for the oystercatchers. Climate change, sea-level rise, and loss of oyster reefs are likely to continue to drive oystercatcher habitat loss, thus habitat creation and restoration is likely needed for this breeding population to persist.
The results of this research were recently published in the Journal Estuaries and Coasts. Scientists and land managers are working on ways to create and enhance habitat for nesting American oystercatchers in the Big Bend and statewide. Stay tuned for an article about what is being done to gain new ground for nesting American oystercatchers.
Vitale, N., Brush, J. & Powell, A. Loss of Coastal Islands Along Florida’s Big Bend Region: Implications for Breeding American Oystercatchers. Estuaries and Coasts (2020). https://doi.org/10.1007/s12237-020-00811-3
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