Embracing dynamic design for climate-resilient living shorelines

As natural marshes are lost to erosion, sea level rise, and human activity, small created marshes, (sometimes with ancillary stabilization structures, and frequently called living shorelines) have gained interest as a replacement habitat; providing both shoreline stabilization and restoration of important ecological functions. These living shorelines enhance ecological function while reducing erosion through the use of marsh plants (Table 1). In all but the lowest energy settings, oyster reefs, low rock structures, or other stabilizing material are frequently used to enhance marsh establishment. Due to their ability to stabilize the shoreline with minimal impact to the ecology, living shorelines are considered a method to increase coastal community resilience to sea level rise (e.g., Sutton- Grier, Wowk, & Bamford, 2015; Van Slobbe et al., 2013) but little consideration is being given to living shoreline resilience under changing climate. Although it has been stated that living shorelines have the capacity to adapt to rising sea levels (e.g., Moosavi, 2017; Sutton- Grier etal., 2015; Toft, Bilkovic, Mitchell, & La Peyre, 2017), their ability to fulfill this potential relies on being designed to incorporate all the processes occurring in natural systems. The extent to which living shorelines can mimic the resiliency of natural marshes and oyster reefs will depend on their setting, design and the type of human maintenance provided. Truly resilient projects will require engineers and ecologists to work together to describe the dynamics of shore line processes under sea level rise and translate this understanding into living shoreline desig

Ecosystem Approaches to Aquatic Health Assessment: Linking Subtidal Habitat Quality, Shoreline Condition and Estuarine Fish Communities

In the Chesapeake Bay, there is currently no comprehensive assessment of aquatic habitat heterogeneity or understanding of the effects of multiple stressors on the viability of these habitats. To assess the use of side-scan sonar technology with specially designed classification software, QTC SIDEVIEW developed by Quester Tangent Corporation as a tool to define subtidal nearshore habitat, two representative watersheds of the Chesapeake Bay were surveyed. Relationships between subtidal habitat and shoreline condition as well as linkages of habitat condition to fish community indices were assessed. Side-scan technology had the ability to image habitat at a resolution of less than 1 meter. Automated seabed classification shows promise as a delineation tool for broad seabed habitat classes. In the James River, relationships between shoreline condition and fish community indices were observed, while no association with bottom type was reflected in the data possibly due to the limited availability of vertical structure in this system. Observed relationships and habitat mapping protocols have the potential to be extrapolated to additional watersheds in the coastal plain, and become tools for future development of habitat indices and ecosystem management

Shallow Water Fish Communities and Coastal Development Stressors in the Lynnhaven River

Coastal development pressures in the Mid-Atlantic have been attributed to significant negative impacts to aquatic ecosystems. The Lynnhaven River watershed, located in the southernmost extent of the Chesapeake Bay and encompassing Virginia Beach, is an example of a shallow-water tidal system under intense development pressure that is confronted with multiple and often conflicting coastal management issues. Rapid development in and around the City of Virginia Beach over the past few decades has led to the loss of natural buffers and habitat (e.g. oyster, wetlands and seagrasses), increased sedimentation, and degraded water quality. The Lynnhaven Ecosystem Restoration Project, led by U.S Army Corps of Engineers, is an effort to collaborate with State and federal partners over a 5-year period to identify and implement the most effective strategies for improving water quality, restoring oysters and seagrasses, and managing siltation. Limited quantitative information exists on the nekton assemblages utilizing shallow water habitats, such as tidal creeks, within the Lynnhaven River restoration area. To document nekton composition, and to investigate potential effects of development stressors, such as dredging and shoreline modification, three sets of paired dredged and undredged tidal creeks were surveyed in the Western Branch of the Lynnhaven River. Fish communities were sampled with multiple gear types once per month for three months (August, September, October, 2006). Abundance, average length and weight, diversity, and fish community indices were estimated for each creek and time period, and dredged compared with undredged systems for resemblance in fish composition and abundance. Tidal creeks within Lynnhaven Bay support diverse and similar fish communities. Slight differences in community structure among creeks may be attributable to the location and size of watersheds. The effects of dredging were not apparent in fish community responses measured as abundance, biomass, diversity, and fish community indices. However, anthropogenic effects may be obscured in the shortterm by the background variability of physical and water quality features of Lynnhaven Bay estuary, and long-term or cumulative effects are not quantifiable due to the dearth of historic information on fish communities. Available historic information may indicate a shift in fish community structure that could be associated with coastal development pressures, such as shoreline alteration and habitat loss of wetlands and oyster reefs. Accordingly, restoration and preservation of critical nursery habitats may augment fish productivity in Lynnhaven Bay

Large Projected Population Loss of a Salt Marsh Bivalve (Geukensia demissa) from Sea Level Rise

Salt marshes and their inhabitants are being displaced by climate change and human development along the coastline. One inhabitant, the ribbed mussel (Geukensia demissa), forms a mutualistic relationship with smooth cordgrass, Sporobolus alterniflorus, along the US Atlantic Coast. Ribbed mussels stabilize the marsh, remove particulate matter from the water column, and promote denitrification, thereby improving local water quality. To quantify the potential effects of SLR on ribbed mussel abundance and resulting impacts on water quality functions, we compared the current and projected future (2050) spatial distributions of ribbed mussels in Chesapeake Bay assuming an intermediate SLR for the region. We found that ribbed mussel abundance was reduced by more than half due to a combination of drowning marshes, coastal squeeze, and a shift from higher to lower quality habitat. Mussel losses were greatest along the mainstem of the Chesapeake Bay, with modest gains in the headwaters. Our results highlight the importance of permeable land cover (including living shorelines) in the future tidal extent to promote marsh transgression for future mussel populations. The projected mussel abundance reductions will result in a \u3e 50% reduction in mussel-mediated filtration and nitrogen processing, ultimately reducing the resilience of marshes in the system

Examining derelict pot impacts on harvest in a commercial blue crab Callinectes sapidus fishery

Pot fisheries occur worldwide with a significant proportion of the gear becoming derelict. Derelict pots induce detrimental ecological and economic impacts, and more recently were found to reduce blue crab harvests in the Chesapeake Bay commercial fishery. We simulated the presence of derelict pots near actively fished pots in seasonal field experiments to quantify the effect derelict pots have on blue crab harvest. Derelict pots reduced harvests by 30% during the summer, but not during the fall. Female blue crab capture rates were consistently lower when derelict pots were present; while capture rates of the less abundant males were not negatively affected by derelict pots. Variable responses to derelict pots may be due to seasonal differences in female and male blue crab behavior and movements. The costly effect that derelict pots have on harvest should be investigated in other pot fisheries to recognize the magnitude and mechanisms behind these impacts

Changes in plant communities of low-salinity tidal marshes in response to sea-level riselow-salinity tidal marshes in response to sea-level rise

As sea-level rises, low-salinity tidal marshes experience greater flooding with more saline water. In the Chesapeake Bay estuary, we compared the 1980 and 2014 tidal marsh inventories (TMIs) of plant communities from James City County, Virginia, USA, with respect to the spatial distribution of two species—the invasive reed Phragmites australis and native salt marsh grass Spartina alterniflora–plus overall species richness. Since the 1980 TMI, the total area of low-salinity tidal marshes in which P. australis occurred increased from 0.46 km2 to 6.30 km2 in 2014. Between TMIs, however, the total area of low-salinity marshes occupied by S. alterniflora increased by only 0.02 km2. Species richness in low-salinity tidal marshes decreased from 41 to 25 between TMIs. To assess seedling emergence under increased flooding and salinity, we completed two seed bank germination experiments using soil samples collected from six low-salinity marshes containing established P. australis stands. In the first experiment, more seedlings emerged in the two low-salinity (0 vs. 5 ppt) treatments after seven weeks, irrespective of flooding (water 3.75 cm below vs. at soil surface), but no P. australis or S. alterniflora germinated. For the second experiment, we added seeds of P. australis and S. alterniflora to soils exposed to the same flooding and salinity treatments to test the impact of these plant competitors on seedling emergence. No difference in number of seedlings was detected among treatments, but the number of species and their relative abundance was significantly affected by flooding (ANOSIM, R = 0.138, P \u3c 0.001). The presence of P. australis and S. alterniflora seedlings appeared to shift the physical factor more influential on seedling emergence from salinity to flooding. For both seed bank experiments, more seedlings but not more species emerged from soils collected from marshes where P. australis coverage was P. australis and S. alterniflora—a trend expected to continue here and in other riverine estuaries of the Atlantic and Gulf Coasts

The application of oyster reefs in shoreline protection: Are we over-engineering for an ecosystem engineer?

Oyster reef living shorelines have been proposed as an effective alternative to traditional coastal defence structures (e.g. bulkheads, breakwaters), with the benefit that they may keep pace with sea-level rise and provide co-benefits, such as habitat provision. However, there remains uncertainty about the effectiveness of shoreline protection provided by oyster reefs, which limits their broader application. We draw evidence from studies along the east and gulf coasts of the United States, where much research and implementation of oyster reef restoration has occurred, to better define the existing gaps in our understanding of the use of restored oyster reefs for shoreline protection. We find potential disconnects between ecological and engineering functions of reefs. In response, we outline how engineering and ecological principles are used in the design of oyster reef living shorelines and highlight knowledge gaps where an integration of these disciplines will lead to their more effective application. Synthesis and applications. This work highlights the necessary steps to advance the application of oyster reef living shorelines. Importantly, future research should focus on appropriate designs and conditions needed for these structures to effectively protect our coasts from erosion, while supporting a sustainable oyster population, thereby providing actionable nature-based alternatives for coastal defence to diverse end-users

Targeted “Hotspot” Removal of Derelict Blue Crab Traps (VA, MD)

In the winter of 2019/2020, five commercial watermen spent a cumulative total of 120 removal days on the water and collected 971 derelict blue crab traps which contained 985 blue crabs, 239 fish (oyster toad fish, black sea bass, flounder, pig fish, striped bass, speckled trout, perch, butterfish), 31 diamond back terrapin (a listed “species of concern”), and one duck. A majority of the traps removed were metal as opposed to vinyl coated (83% and 17%, respectively). Bycatch was present in 43% (346) of metal traps and 44% (72) of vinyl coated traps removed. On average, the instantaneous capture rates were similar for both trap types with an average of 1.0 crab captured per trap and 0.25 fish captured per trap. In addition, 10 abandoned eel traps were removed which contained 2 blue crabs, 3 fish, and 1eel

Diamondback Terrapin Bycatch Reduction Strategies for Commercial and Recreational Blue Crab Fisheries

Diamondback terrapin (Malaclemys terrapin) is considered a keystone species for its influence on community structure of tidal marshes. Terrapins exhibit strong habitat and nest site fidelity, and have relatively small home ranges (\u3c 2 km), so that sub-populations tend to be spatially discrete. Terrapins rely on open water, wetlands, and adjacent uplands at various stages of their life-cycle, so the quality and connectivity of these habitat patches is critical to population persistence. Terrapin is listed in Virginia as a species of Very High Conservation Need based on threats due to nest predation and drowning of adults in crab pots. Terrapin population declines, reduced growth, and changes in sex ratios have been directly attributed to bycatch mortality in commercial crab pots. Our overall project goal was to characterize essential terrapin habitats toward development of bycatch reduction strategies for managing commercial and recreational blue crab fisheries. In a pilot study area surrounding the mouth of the York River, Virginia, our approach was to 1) geospatially define suitable terrapin habitat based on natural features, 2) integrate spatial datasets to develop a Vulnerability Index of terrapin habitats and define potential resource conflict areas where crab pots correspond to essential terrapin habitat, and 3) conduct terrapin and crab pot counts in habitats with varying suitability to test predictions. Suitable terrapin habitat (full connectivity among habitat metrics) accounted for over 50% of all terrapin observations, and another 45% of observations occurred in areas where only one habitat metric was absent. In 96% of these cases, the absent metric was SAV presence. In contrast, full habitat connectivity was determined for only 5% of areas where terrapins were absent. Within the pilot study area during a two year retrieval program, 2872 derelict pots were removed. Of these, 22% were within shallow waters (≤ 2 m) where terrapins typically reside. Of the suitable terrapin habitat (70km2 ), 21% (15 km2 ) was considered vulnerable to crabbing pressures (10% highly and 11% moderately vulnerable). Approximately 15% of the study area was considered to be potential resource conflict areas for terrapin and crabbing. Candidate zones for the targeted application of blue crab fishery management actions to reduce terrapin bycatch include the Severn River, Perrin River, Guinea Marshes, and south of Gwynn Island. The integration of spatial information on terrapin habitat and crabbing pressure in a single framework will allow managers to identify areas where terrapins are most likely to encounter threats and target conservation efforts in those areas. In resource conflict areas, there are several management options that can be used in combination 1) Require use of bycatch reduction devices (BRDs) on commercial & recreational crab pots 2) Avoid particular habitats (e.g. small tidal creeks) or establish fishing exclusion zones 3) Educate – design public education programs to • promote the voluntary use of BRDs, and • communicate to recreational boaters the ramifications of severing buoy lines of active crab pots 4) Promote proper use of gear (e.g. retrieving pots regularly to minimize terrapin mortality). With further refinement to improve the predictability of terrapin occupancy, the terrapin habitat vulnerability model is transferable to all coastal areas where diamondback terrapins occur and where blue crabs are commercially and recreationally fished—from southern New England to Texas