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Coastal & Estuarine Science News (CESN)

Coastal and Estuarine Science News (CESN) is an electronic publication providing brief summaries of select articles from the journal Estuaries and Coasts that emphasize management applications of scientific findings. It is a free electronic newsletter delivered to subscribers on a bi-monthly basis.

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November 2018

Table of Contents

Healthy Habitat at Restored Reefs
Can Salt Marshes Keep Up with Rising Seas?
Tracking Marsh Response to the Deepwater Horizon Oil Spill
Proving the Worth of Living Shorelines

No difference in nekton between natural and created reefs

Oyster reefs provide a host of ecosystem services, including habitat for nekton—motile animals such as fishes and shrimp. However, oyster reefs have been dramatically depleted throughout the East and Gulf Coasts due to overharvesting, pollution, and disease. State agencies and other coastal managers have been working to restore oyster reefs in many places, but long-term monitoring of these “created” reefs is often lacking. Using seine nets and passive fishing devices called Breder traps, the authors of a new study compared the nekton communities of four naturally occurring intertidal oyster reefs with those found at four created intertidal reefs in a North Carolina estuary. They found no significant difference between the natural and created reefs in nekton abundance, species richness, or size, and both reef types hosted a similar range of species.

The created reefs were ten years old at the time of the study, and a decade of growth and development likely contributed to their robust nekton communities. The authors speculate that other factors included the created reefs’ relatively small size and close proximity to natural reefs, allowing them to be easily colonized, and their location in the intertidal zone, where fish and shrimp are forced to be less choosy about where they forage during the brief period of submergence. Further research would be helpful to learn more about how factors such as choice of building materials affect the nekton communities that created reefs attract, but this study provides encouraging results for managers engaged in oyster reef restoration.

Source: Rutledge, K.M., T. Alphin, and M. Posey. 2018. Fish Utilization of Created vs. Natural Oyster Reefs (Crassostrea virginica). Estuaries and Coasts. DOI: 10.1007/s12237-018-0433-4

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Can Salt Marshes Keep Up with Rising Seas?

"Elevation capital" an indicator of marsh resilience to sea level rise

Sea level rise and human impacts to coastal areas are threatening the ability of salt marshes around the world to maintain their elevation relative to the tide and support vegetation. The authors of one recent study tracked elevation change and accretion at five sites spread across salt marshes in New York City’s Jamaica Bay, and their results show that “elevation capital”—the marsh's elevation relative to the growth range of vegetation—is a fundamental key to whether a saltmarsh is resilient to climate change.

The study found that two marshes with high elevation capital maintained their relative position high within the tidal range throughout the study, keeping pace with local sea level rise. A marsh located low in the tidal frame, on the other hand, did not support continuous coverage of marsh vegetation and gained no elevation over the course of the 14–year study. Dredged sediment was deposited on a portion of this marsh near the beginning of the study period to raise the elevation in an effort to restore it, and the restored marsh supported continuous vegetation cover. Although elevation gain in the restored marsh initially lagged behind sea level rise, it caught up during the last five years of the study.

The authors of the study point out that a marsh becomes vulnerable to degradation when its elevation gain begins to lag behind sea level rise, which can happen long before changes to its vegetation become visible thanks to high elevation capital. However, their results show that restoration efforts can stabilize a degrading marsh. Even if the restored marsh doesn’t keep up with sea level rise forever, they argue, practices such as dredged sediment deposition can boost its resilience by building up its elevation capital—essentially making a deposit in the marsh’s elevation bank account.

Source: Cahoon, D.R., J.C. Lynch, C.T. Roman, J.P. Schmit, and D.E. Skidds. 2018. Evaluating the Relationship Among Wetland Vertical Development, Elevation Capital, Sea-Level Rise, and Tidal Marsh Sustainability. Estuaries and Coasts. DOI: 10.1007/s12237-018-0448-x

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Tracking Marsh Response to the Deepwater Horizon Oil Spill

Benthic infauna recovery associated with Spartina and benthic algae

While other studies have examined the recovery of salt marshes in the wake of the Deepwater Horizon oil spill, a new project used multivariate statistics to measure the response of the benthic infaunal community—the small invertebrates that live in the mud—in relation to a suite of environmental characteristics.

The salt marshes of Barataria Bay, Louisiana, received some of the worst oiling from the Deepwater Horizon spill. From 2–6.5 years after the spill, researchers collected soil cores from more than 20 sites around the bay to monitor the infaunal community’s recovery. The communities at sites that experienced less intensive oiling had begun to resemble un-oiled sites by two years after the spill. Heavily oiled sites, in contrast, remained distinct at the end of the study even though a number of benthic taxa recovered within the 6.5-year period; it will likely take more than a decade for the communities at heavily oiled sites to fully recover. The biomass of Spartina (which provides crucial habitat) and benthic algae (an important food source for the infaunal community) were the strongest indicators of recovery. Juncus (a second foundational marsh plant) recovered more slowly than Spartina, however, as did multiple environmental factors (belowground biomass, dead biomass, bulk density and pH), and a few infauna species lagged behind overall recovery in step with these factors.

The researchers behind the study recommend planting Spartina to speed up ecosystem recovery.  However, planting alone will not quickly foster recovery of infaunal species that respond to soil quality. One possibility would be to fertilize initial plantings to promote a more rapid buildup of belowground biomass. Such strategies may help damaged salt marshes bounce back faster in the wake future destructive events.

Source: Fleeger, J.W., M.R. Riggio, I.A. Mendelssohn, Q. Lin, D.R. Deis, D.S. Johnson, K.R. Carman, S.A. Graham, S. Zengel, and A. Hou. 2018. What Promotes the Recovery of Saltmarsh Infauna after Oil Spills?. Estuaries and Coasts. DOI: 10.1007/s12237-018-0443-2

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Proving the Worth of Living Shorelines

Living shorelines reduce erosion rates in North Carolina

Hard structures such as revetments and bulkheads are popular tools for stabilizing shorelines, but they have a wide range of undesirable side effects, including habitat loss and altered sediment transport. Although “living shorelines” that incorporate vegetation and native material are one alternative, hard data on how well they actually stabilize eroding shorelines is lacking. To remedy this, researchers in North Carolina examined how sill-type living shorelines that encompassed a range of techniques and materials had changed since installation.

The researchers surveyed shoreline positions at 17 living shoreline sites and nine adjacent control sites, comparing current conditions with aerial photos from before the living shorelines were installed. Of the 17 living shoreline sill segments, 12 showed reduced rates of erosion after installation, six of which had begun accreting. Sites where erosion had increased since installation tended to be newer, and the authors believe that some sites may simply need more time to realize their potential. Overall, living shoreline sites experienced significantly less erosion than control sites. Two sites where erosion was greater than at adjacent control sites had specific problems associated with the design of the structural segments of the living shoreline.

More research comparing living shorelines to other shoreline stabilization methods and looking at the effects of different design characteristics would be useful for guiding coastal management strategies in the future. However, the results of this study show that living shorelines not only preserve habitat as compared to shoreline hardening structures—they’re also effective at slowing the erosion of vulnerable estuary habitat.

Source: Polk, M.A. and D.O. Eulie. 2018. Effectiveness of Living Shorelines as an Erosion Control Method in North Carolina. Estuaries and Coasts. DOI: 10.1007/s12237-018-0439-y

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