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A Regional Approach to Multiple Stresses in Mid-Atlantic Shoreline Habitats

blue crab and white perch
Healthy tidal marshes and other natural shoreline habitats are essential to estuarine species such as the Chesapeake blue crab (left) and white perch (right, photo from Maryland Saltwater Sportfisherman’s Association).

NOAA’s Center for Sponsored Coastal Ocean Research has recently initiated a large-scale research project in the Chesapeake Bay and Delmarva Coastal Bays to evaluate the regional living resource impacts of extensive modification of shoreline habitats driven by climate change, pollution and other stressors. The information produced by this project is intended to help transform management from the current “parcel by parcel” approach to one in which regional ecosystem impacts provide a strong component of the decision-making process.

Issue

The Mid-Atlantic region benefits from a wealth of resources and activities that depend on healthy coastal habitats. However, these habitats are being degraded by multiple stresses including extensive hardening of shorelines due to climate-driven sea level rise, increasing shoreline development, land use changes in coastal watersheds, pollution, and invasions of non-native species.

Coastal development has been intense along the Chesapeake Bay and the Delmarva Coastal Bays, threatening important habitats such as wetlands and seagrass beds. Up to 80% of shoreline in some Chesapeake Bay tributaries may be altered with bulkheads and riprap (structure made of different kinds of rock or rubble), in a process called shoreline hardening. Increased inputs of nutrients, sediments and contaminants from the watershed, and invasive species crowding out native plants and animals, also threaten these habitats. Resource managers need sound science to fill significant gaps in our understanding of the local and regional impacts of shoreline hardening and thereby enable shoreline use policies that are protective of valuable living resources in these coastal environments.

Management/Policy Issues

hard shoreline structures and riprap
Hard shoreline structures such as bulkhead (left) and riprap (right) disrupt natural shoreline habitats.

Management agencies are struggling to balance the pressures of coastal development with the conservation and protection of the coastal environment. Predictions of climate change and sea level rise can encourage the use of bulkheads and riprap to protect shoreline structures, but these impede the natural processes necessary for near-shore ecosystems.

Often, one project that creates a bulkhead or riprap will have a negligible effect on the overall estuarine system. But multiple projects can have a cumulative impact or can exceed a “tipping point” that could be catastrophic for regional populations of living resources. Is there a minimum amount of natural shoreline needed to sustain estuarine habitats and species? What is that minimum threshold, and what are the consequences if natural shorelines decline past the threshold? Can the system recover if natural habitats are restored? All of these questions require a comprehensive, multi-disciplinary regional ecosystem-scale approach.

Working in partnership with management agencies, this project will develop and apply models that predict the cumulative impacts of these multiple stressors, test for threshold effects, estimate losses of economically important species, and support more informed and proactive environmental management decisions.

Approach

The overall goal of this project is to improve the capability of predicting the combined effects of shoreline hardening, watershed land use and Phragmites invasion of tidal wetlands on habitat quality for seagrasses and estuarine animal species. Studies will relate the presence and condition of sub-tidal seagrasses and estuarine animals to watershed land use (dominated by forest, agriculture, or developed land) and other factors such as wave energy, sediment supply, and water oxygen levels. Abundances of estuarine fauna such as blue crabs, white perch, mummichog and waterfowl will be related to adjacent shoreline type (natural, riprap, bulkhead, or shallow beach). The project will also compare estuarine habitats and fauna in tidal wetlands with or without the invasive species Phragmites. The project scientists will determine the effects of shoreline changes through before and after comparisons, including the conversion of natural to hardened shoreline, the restoration of hardened shoreline back to natural shoreline, and the eradication of Phragmites stands to allow regrowth of native wetland plants.

Phragmites and Spartina
The invasive marsh plant Phragmites (left) has replaced much of the native Spartina marshes (right).

Once relationships are determined between these multiple factors and the health of estuarine habitats and species, then predictions can be made about the impacts of future watershed and shoreline development.

Expected Outcomes

Project scientists will work with relevant management agencies throughout the course of the project to develop predictive models and other tools that can be used to better inform decision-making related to shoreline habitats. For example, mathematical models can be used to synthesize complex information and predict impacts of wave energy and underwater light limitation on submerged aquatic vegetation (SAV), and relate SAV presence and abundance to watershed and estuarine characteristics, especially land use and shoreline hardening. An improved model of factors and thresholds contributing to Phragmites invasion of wetlands will help to identify appropriate areas for marsh restoration and protection. Enhanced models will predict future habitat suitability for blue crabs, white perch, mummichogs, and other species, and integrate the effects of altered shorelines into predictions of fisheries and ecosystem productivity. These models can be used by the project’s management partners to better protect and restore the vital shorelines of the Mid-Atlantic region.

Research Partners

This project is led by Dr. Tom Jordan of the Smithsonian Environmental Research Center (SERC) and includes other researchers from SERC, the Virginia Institute of Marine Sciences, the University of Maryland, the University of Delaware, Pennsylvania State University, the Maryland Department of Natural Resources, and the U.S. Geological Survey.

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