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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 3

Table of Contents

Macroinfauna Recovery After the Deepwater Horizon Spill

Heavily oiled marshes will likely require more than a decade to recover, if at all

In 2010, the Deepwater Horizon oil spill released 4.1 million barrels of crude oil and contaminated more than 1,000 kilometers of coastal wetlands in Louisiana. This impacted a wide range of plants and animals, including macroinfauna—macroinvertebrates living within the sediment—which often serve as indicators of marsh health, productivity, and resilience following disturbance. Researchers monitored macroinfaunal response to the spill in Louisiana’s Barataria Bay during early (2011–2012), middle (2013–2017), and late (2017–2018) stages of recovery in seven heavily oiled areas, seven moderately oiled areas, and seven lesser-impacted reference sites that experienced no visible oiling.

Diversity and abundance of macroinfauna were low in the early recovery stage across all marshes. Community structure at heavily oiled sites was much different than both reference and moderately oiled sites in all three stages, particularly during the middle recovery period when abundance and diversity peaked. In contrast, community structure at moderately oiled sites differed from reference sites during the middle recovery period, but not by the late recovery period.

The authors suggest that macroinfaunal communities in moderately oiled sites can recover in terms of species composition and abundance (relative to reference sites) in about eight years post-spill. However, macroinfauna in heavily oiled sites will take more than a decade. In fact, three of the heavily oiled sites were along the marsh edge in places that experienced severe oil-induced erosion and were permanently lost to open water. Changes in macroinfaunal communities likely affected ecosystem-level processes, particularly given that plants suffered near-complete mortality in heavily oiled marshes and exhibited reduced above- and belowground biomass in moderately oiled marshes.

Source: Pant, M. et al. 2025. Recovery of Saltmarsh Macroinfauna After the Deepwater Horizon Oil Spill. Estuaries and Coasts. DOI: 10.1007/s12237-025-01520-5

Image: Sampling the plots / David Johnson

Where Else Can Living Shorelines Be Useful?

An experimental comparison of shoreline designs 

Creating oyster-supporting habitat close to the marsh edge is a nature-based option for shoreline stabilization in areas such as the southeastern US, where oysters grow in intertidal areas. Once established, the reefs can help reduce marsh loss (or even support its expansion) while also providing additional benefits such as improving water quality.

To help guide the creation of oyster reef habitat, researchers in South Carolina investigated the performance of four types of living shoreline materials: bagged oyster shell reefs, cement-coated manufactured wire reefs (MWRs, modeled after crab traps), and two natural fiber treatments including coir logs made of coconut fibers and blocks composed of aspen fibers encased in a knit fabric. These were deployed at a dozen sites encompassing a broad range of shoreline conditions along the state’s coast—including previously avoided areas with steep banks, very fine substrate, or high wave exposure. The sites were monitored for six years.

The fiber-based treatments performed poorly, getting lost or becoming deteriorated at all the sites within two years. The bagged oyster shells and wire reefs largely persisted and supported oysters, with bagged shells performing the best while requiring the least amount of maintenance. Protected marsh areas behind those oyster-supporting treatments increased in elevation, experienced less marsh erosion than controls, and, in some cases, exhibited lateral marsh expansion. The best-performing treatments were in areas with moderately steep bank slopes, in substrates that were less than 85% silt and clay, and installed within three meters of the marsh edge and above the bottom of the tidal frame. Sites meeting all of these criteria showed several meters of marsh expansion within five years.

Site selection, material choice, and the placement of materials within the tidal frame all influence the effectiveness of living shorelines. Additionally, the results from this work showed that oyster reefs could thrive under a broader range of bank slopes than initially thought. Side-by-side comparisons are extremely useful, and these results have already been used to provide installation guidance and in the development of new regulations adopted by the state.

Source: Tweel, A. et al. 2025. Investigating the Effects of Site Characteristics and Installation Material Type on Intertidal Living Shoreline Performance in Coastal South Carolina, USA. Estuaries and Coasts. DOI: 10.1007/s12237-025-01515-2

Image: (A) Manufactured wire reef, (B) bagged shell reef, (C) blocks of aspen fibers, (D) coir log treatment / The Authors

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The Blob is a Harbinger of Things to Come

Using a marine heatwave to understand habitat responses 

An unusual marine heatwave, known as the “Blob,” was observed on the Pacific coast beginning in late 2013, followed by a strong El Niño event in 2015 to 2016. One of the consequences of these anomalous events was increased flooding of tidal marshes—which provided researchers with an opportunity to directly observe the potential effects of increased sea level on marsh plant communities. They studied three California estuaries where sea levels increased an average of 15 centimeters: Tijuana Estuary, Carpinteria Salt Marsh, and Elkhorn Slough. Using a combination of field work, remote sensing imagery, and existing long-term monitoring data, the team examined responses of the ecotone between the succulent perennial pickleweed (Salicornia pacifica, the common mid-marsh dominant) and plants or mudflats in the lower marsh.

Despite spanning 600 kilometers, all three estuaries showed a rapid, sharp decline in Salicornia, particularly at lower elevations. In the Tijuana River Estuary, areas of Salicornia dieback were initially colonized by the low-marsh dominant, California cordgrass (Spartina foliosa). In the other two systems, which did not have Spartina, low Salicornia marsh areas were converted to mudflat. Although Salicornia began to recover after tidal inundation decreased, it did not reach pre-Blob levels in any of the estuaries before the end of the study period.

These case studies revealed how sensitive tidal marshes are to sea–level changes. They also show the value of long-term monitoring for detecting ecotone shifts along with other habitat responses to sea level changes.

Source: Uyeda, K.A. et al. 2025. Increases in Sea Level Associated with a Marine Heatwave Drive Tidal Marsh Habitat Shifts. Estuaries and Coasts. DOI: 10.1007/s12237-025-01530-3

Image: Salicornia pacifica and Spartina foliosa in the low marsh at the Tijuana Estuary / Kellie Uyeda

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How Juvenile Bull Sharks Respond to Freshwater Input

Implications for flow restoration in Florida 

Juvenile bull sharks (Carcharhinus leucas) are top predators in their subtropical estuarine nurseries, but their presence depends on many factors likely linked to climate change and upstream modification of their watersheds. To better understand what influences the presence and abundance of bull sharks in their nurseries, researchers examined 20 years of shark sampling data (which includes 1,186 immature bull sharks) collected monthly from Southwest Florida’s Ten Thousand Islands Estuary. They focused on three bays with differences in freshwater input—one with restricted flow, one with enhanced flow, and one with little human alteration—as well as differences in a suite of abiotic and biotic factors.

The abundance of juvenile bull sharks was most strongly associated with salinity. The highest abundances were observed during the wet season, especially in the bay with the artificially enhanced freshwater flow and lowest minimum salinity. Juvenile sharks were most abundant at salinities around 5 PSU and decreased with increasing salinity up to 10 PSU. Temperature affected abundance but to a lesser degree; catch rates were higher with rising temperatures, peaking at 27^oC. Restoration will likely raise salinity in the artificially freshwater enhanced bay, potentially reducing its appeal.

These findings show that identifying and then managing for factors such as salinity can help drive species abundance—in this case, determining suitability for juvenile bull sharks based on freshwater flow. More generally, they provide support for the need to assess impacts of large-scale ecosystem restoration projects on wide varieties of taxa, as there could be unexpected consequences for species outside the restoration’s initial scope. This is particularly important for upper trophic level species that may not be considered in initial restoration outcomes. Because large predators can have cascading impacts on their prey and ecosystems, understanding how they’re impacted by climate change and human actions will help make better predictions about how to manage these systems.

Source: Zikmanis, K. et al. 2025. Legacies of Ecosystem Modification: Factors Affecting Long‑Term Variation in the Abundance of Juvenile Bull Sharks in a Subtropical Estuary. Estuaries and Coasts. DOI: 10.1007/s12237-025-01508-1

Image: Bull shark sampling / Kristine Zikmanis