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Coastal & Estuarine Science News (CESN)

The mission of Coastal & Estuarine Science News (CESN) is to highlight the latest research in the journal Estuaries and Coasts that is relevant to environmental managers. It is a free electronic newsletter delivered to subscribers on a bi-monthly basis. Sign up today!

2025 Issue 6

Table of Contents

Including Seagrass Beds in Shoreline Stabilization

Remember to consider the subtidal slope in living shoreline designs

Seagrass beds provide multiple benefits, but they are not generally incorporated into living shoreline designs. Understanding the relationship between natural shorelines, stabilized shorelines, and seagrass beds will help managers design more connected projects with potentially greater ecosystem function and resilience.

Working in Florida’s Mosquito Lagoon, researchers examined factors that affect the presence and persistence of seagrass beds, as well as the effects of living shorelines on adjacent seagrass beds. They coupled modeling with geospatial analyses of aerial imagery taken between 2011 and 2021. In 2023, they measured shoot density in naturally recruiting seagrass beds growing adjacent to both intact shorelines and living shorelines stabilized two to three years prior with recycled oyster shell, oyster shell metal gabions, and biodegradable cement­–jute cones.

Overall, across all shoreline types, the model predicted that seagrass will be present for longer at sites with shallower nearshore depths and wider intertidal zones. The living shorelines at Mosquito Lagoon were successful in reducing shoreline erosion and attenuating wave energy, both of which are important for maintaining seagrass persistence. However, field monitoring found greater seagrass density at natural, uneroded shorelines with gradual subtidal slopes, compared to any of the living shoreline designs within three years of deployment. Natural shorelines with high seagrass persistence also experienced reduced rates of shoreline retreat. Of note, when depth and slope were held at mean values, the model did not predict differences in seagrass density between shoreline types—whether natural or stabilized. The observed difference was attributed to preexisting differences in shoreline morphologies.

The findings highlight the importance of preserving slowly erodingshorelines with low subtidal slope angles for supporting seagrass meadows. The authors recommend incorporating seagrass beds into living shoreline projects—either directly through co-restoration, or indirectly through designs that are conducive to natural seagrass recruitment.

Source: Benson, G.W. et al. 2025. Examining the Relationship Between Nearshore Seagrass and Living Shorelines in a Subtropical Estuary. Estuaries and Coasts. DOI: 10.1007/s12237-025-01595-0

Are Hard Clams and Restored Seagrass Fighting for Bottom Space?

A new predictive model for seagrass distribution

There are growing conflicts between the use of nearshore habitat for marine aquaculture versus conservation of natural habitat. This issue is of concern in coastal lagoons on the east coast, where bottom-use conflict is potentially brewing between hard clam (Mercenaria mercenaria) aquaculture and restored eelgrass (Zostera marina) meadows. Currently, direct interaction can be avoided by not leasing areas for aquaculture where seagrass is present, but eelgrass restoration and hard clam aquaculture have similar requirements and few studies have examined their overlap.

To fill this data gap, researchers analyzed 20 years of aerial imagery of shallow lagoons along the coast of the Delmarva Peninsula in Virginia. They evaluated trends in eelgrass cover, clam aquaculture, and their spatial overlap with each other, as well as their distribution relative to an array of environmental variables. The team then used the resulting dataset to construct predictive models to examine potential future spread of seagrass and overlap with clam aquaculture.  

From 2001 to 2021, both seagrass area and the area used for clam farming increased significantly. Seagrass generally occurred deeper than aquaculture and in areas with greater frequency of warm sea surface temperature, higher fetch, and sediments with a lower sand fraction. The model also suggested that both seagrass area and clam farms could continue to expand with relatively minimal direct overlap under current conditions.

Despite the perception of growing bottom-use conflict between aquaculture and seagrass, that may not be the case, and especially when assessed on a regional scale. Evaluating interactions between different bottom uses at these broad scales is important for implementing useful management policy.

Source: Breitenbeck, G.A. et al. 2025. Bottom-Use Conflicts in Shallow Coastal Zones: Hard Clam (Mercenaria mercenaria) Aquaculture and Restored Seagrass (Zostera marina). Estuaries and Coasts. DOI: 10.1007/s12237-025-01593-2 

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Automated Detection of Boat Scarring in Seagrass Beds with ArcGIS

A deep learning tool to help monitor seagrass disturbance 

Seagrasses are found in shallow areas, making them vulnerable to boat propellers. In fact, much of the remaining seagrass along the U.S. southeastern coast exhibits substantial scarring from boat traffic. Although identifying the location and abundance of seagrass scarring is needed to guide management interventions, quantifying the amount of seagrass scarring is time-consuming, as it is usually done by manual digitizing. New machine learning tools have the potential to detect seagrass scars, but these deep learning tools can be inaccessible to natural resource managers.

A team of researchers wanted to develop a more efficient method for quantifying the extent of seagrass scarring that did not rely on manual digitization. They used aerial imagery from 2020 and digitized maps of continuous seagrass cover to manually identify a subset of seagrass scars in select regions of Tampa Bay. Then, with the new Deep Learning toolset in ArcGIS Pro 3.0, the team used the training data to develop a model that detects all seagrass scars in the bay using data from remote sensing.

The model detected 23,488 seagrass scars across continuous seagrass imagery with minimal false positive and false negative results. Using the scarring identified from the model, the team was able to create a map that identifies priority areas for management and public outreach campaigns.

Seagrass scarring hasn’t received a lot of attention, primarily because of the difficulty of quantifying the extent and trends over time. By utilizing ArcGIS Pro, this new deep learning tool provides a potentially efficient and cost-effective approach to characterize the extent of scarring. The model can help managers prioritize hotspots in need of intervention or evaluate the relative role of scarring compared to other threats. This can lead to a more complete approach that considers how multiple stressors influence seagrass cover.

Source: Lawson, K.M. & Q.M. Tuckett. 2025. Semi-automated Detection of Seagrass Scars in Tampa Bay from Aerial Imagery: An Application for ArcGIS Pro Deep Learning. Estuaries and Coasts. DOI: 10.1007/s12237-025-01606-0

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Seagrass Can Be Restored in Open-Coast Habitats Too

Broadening the scope of seagrass recovery 

Seagrasses function as ecosystem engineers, forming habitats that support diverse fish and invertebrate assemblages. In Southern California, most seagrass restoration work has been conducted in shallow, sheltered estuarine environments. Although open-coast seagrass systems do occur along the exposed coastlines of the Channel Islands, there has been little investigation of restoration in these higher-energy environments.

Researchers wanted to track the survivorship of transplanted seagrass and assess restoration success at the open-coast site of Button Shell on Catalina Island. They transplanted mature eelgrass (Zostera marina) shoots from a nearby donor meadow and compared shoot density, fish abundance, and community structure at the transplant site to seven nearby reference sites from 2021 to 2024.

Restoration of the eelgrass meadow was a success. The meadow created by transplanted shoots expanded in area, and after only two years, seagrass at the transplant site resembled (and even exceeded) that at nearby reference sites in terms of shoot density and blade length. Furthermore, the restoration site supported a similar fish community as reference sites.

Overall, the authors conclude that restoring seagrass and creating new meadows is feasible even at open-coast sites that are environmentally much different than typical estuarine restoration sites. They recommend expanding efforts beyond conventional restoration spaces towards these often isolated and overlooked open-coast locations. These areas offer far more available space, which will be increasingly important as climate change and human impacts continue to threaten seagrasses and reduce the availability of suitable habitat for future restoration projects in bays and estuaries.

Source: Sanders, R.D. et al. 2025. Open-Coast Eelgrass (Zostera marina) Transplant Catalyzes Rapid Mirroring of Structure and Function of Extant Eelgrasses. Estuaries and Coasts. DOI: 10.1007/s12237-025-01609-x

Image: Adam Obaza