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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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May 2021

Table of Contents

What Does Restoration Success Look Like?
Lessons From Two Decades of Native Oyster Restoration

Fishing in the City
Getting More Bang for the Buck in Marsh Restoration

What Does Restoration Success Look Like?
Comparing a dozen projects on the Upper Texas Coast

Coastal wetland restoration projects vary in terms of construction techniques, planting strategies, and a host of site-specific features, making it hard to draw generalizations based on an individual project. This study looked at data collected from 13 marsh restoration sites located in the Chenier Plain ecosystem on the Upper Texas Coast. Some of them used excavated sediment to form discrete mounds and terraces, while others used dredged material from a nearby port to build areas to the level of the marsh platform. Some were planted with native Spartina alterniflora, whereas others were left unplanted to be colonized naturally; some were close to developed areas and others were further away.

Although none of the restored areas had plant species assemblages that closely resembled reference conditions (which were dominated by Spartina patens), most of the sites attained reasonable levels of vegetation cover regardless of whether they were planted. Plant biomass and percent cover in marshes restored with dredged material were similar to reference conditions and up to 70% higher than those constructed with excavated sediment, suggesting that construction technique is important. Interestingly, proximity to roads, buildings, and other hardened boundaries did not influence success: Although anthropogenic alterations limit connectivity with neighboring waterways and wetlands, they did not substantially impede the development of plant communities.

The study brings up a number of salient questions regarding restoration success. Is a project successful if biomass and cover are similar to reference sites even if the plants are different? Will the outcomes change as the projects age? Is vegetation the only metric that should be evaluated? The author points out that labeling any of these individual restoration sites as successes or failures would be too simplistic. For example, the expansive intertidal areas in sites with lower plant cover made them potentially valuable as alternate habitat for aquatic wildlife. This shows that landscape context is important, and that even “failed” restoration projects can be valuable as they help to provide habitat heterogeneity.

Source: Armitage, A.R. 2021. Perspectives on Maximizing Coastal Wetland Restoration Outcomes in Anthropogenically Altered Ecosystems. Estuaries and Coasts. DOI: 10.1007/s12237-021-00907-4

Lessons From Two Decades of Native Oyster Restoration
A decision tree for effective oyster restoration

The Olympia oyster (Ostrea lurida) is a foundation species for estuaries along the west coast of North America, where it creates habitat for numerous other species. With populations at 1% of historic levels, their restoration has become a priority for maintaining ecosystem function of estuaries in a 2,500-kilometer stretch of the Pacific coast. To inform future efforts, researchers collected data and surveyed practitioners from all known Olympia oyster restoration projects from California to British Columbia over the past two decades.  

The combined funding for all 39 Olympia oyster projects was $8.2 million. By contrast, spending for recent eastern oyster (Crassostrea virginica) restoration projects on the Atlantic and Gulf coasts averaged $2.5 million per project. Although cost per area declined significantly with project footprint, larger and more cost-effective projects are relatively rare for this species. Restoration success was high overall, even though most monitoring was narrowly focused, lasted only a few years, and was spread unevenly across the species’ range. Sediment burial and lack of recruitment were the biggest challenges to restoration success.

The synthesis revealed contrasts among regions: Low profile biogenic beds were restored in Washington, for example, while high profile reefs often incorporating concrete were used in California. Aquaculture as a means of seeding restoration beds was used in a minority of projects, though it would enhance establishment of populations in areas with limited reproduction. To help guide practitioners, the team developed a decision support tool that helps local stakeholders determine appropriate approaches to providing conservation benefits to oyster populations and enhancing desired ecosystem services. They recommend that trade-offs among different habitat types and species should be explicitly considered before embarking on an oyster restoration project.

The authors also emphasize the importance of engaging local communities in the process, and point out that regional strategic planning can help prioritize restoration where it’s most needed and most likely to succeed.

Source: Ridlon, A.D. et al. 2021. Conservation of Marine Foundation Species: Learning from Native Oyster Restoration from California to British Columbia. Estuaries and Coasts. DOI: 10.1007/s12237-021-00920-7

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Fishing in the City
The unique ecology of urban estuarine fisheries

Many cities and other urban centers are located near estuaries, where they currently support more than half the world’s population. These urban areas are variously impacted by habitat loss, eutrophication, contamination and pollution, high boat traffic, and the presence of infrastructure—they are also places where people like to fish. The ecology of these aquatic habitats is necessarily intertwined with the social aspects of urban fisheries, both of which must be considered in the management of these unique systems.

A team of researchers synthesized existing literature on exploited species in urbanized estuaries and developed the “urban estuarine fisheries ecology” paradigm, which considers the socio-economic motivations of urban fishers and the unique attributes that affect the productivity of the species they exploit in modified urban estuaries.

Urban marine ecosystems offer an abundance of hard structures suitable for adult finfish, however, they’re also characterized by absence of spawning by exploited species, reduced larval supply, and loss of nursery habitats for juveniles. These fisheries have often shifted away from commercial fishing toward recreational fishing, and the preferential harvest of more predatory sportfish leads to a comparative increase in organisms at lower trophic levels, such as prawns, detritivores, and planktivores.

The team turned to mulloway in Sydney as a case study to illustrate the importance of considering the socio-ecological context of urban fisheries. These highly sought-after sportfish are currently at historically low abundances: Major estuaries for the area lack freshwater inputs important for reproduction and recruitment, and high levels of acoustic noise further impairs reproduction. On the other hand, their food sources, as well as artificial and natural habitats, are abundant throughout. And while pollutants in the sediment accumulate in mulloway, catch-and-release minimizes exposure risk to fishers. Managers responded to these ecological and social factors by supporting the ongoing stocking of juvenile mulloway: Not only does that support mulloway populations, it also supports the needs of the urban angling community.

Source: Taylor, M.D. & I.M. Suthers. 2021. The Socio-ecological System of Urban Fisheries in Estuaries. Estuaries and Coasts. DOI: 10.1007/s12237-021-00916-3

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Getting More Bang for the Buck in Marsh Restoration
A mobile tide gate pays for itself

Engineered defenses such as levees, floodgates, and culverts are built to mitigate floods and protect coastal infrastructure from rising seas—but often to the detriment of marshes. Such practices have degraded highly productive wetland ecosystems, reducing fish and crustacean passage, changing faunal assemblages, and altering food webs. However, the protection of people and the protection of tidal wetlands do not need to be mutually exclusive. Although they come at an additional cost, small and simple infrastructure enhancements that restore flows could be both ecologically sound and economically beneficial over the long term.  

To explore the relative costs and benefits of enhancing flood mitigation and wetland functions simultaneously, researchers turned to three levees installed for protection against 10-year storms on the northern Delaware Bay shoreline of New Jersey. These levees, which restrict tidal flows, have degraded upstream wetlands by reducing salinity, creating standing water, and supporting invasive Phragmites. The study authors considered what would happen if mobile tide gates were installed to allow for unrestricted tidal flow except during extreme weather events that may threaten houses and other properties. In this scenario, up to 226 hectares of tidal wetlands would be potentially restored to a Spartina-dominated landscape due to increased flushing.

Using existing literature, the team estimates that the total economic value of the goods and services provided by those 226 hectares of restored wetlands range from $2.1 to $2.4 million per year. (These are likely underestimates since not all goods and services for tidal wetlands can be valued.) The associated engineering cost for including a mobile gate system is $1.9 million a year—which results in a benefit-cost ratio range of 0.9 to 1.1 over 50 years. Including a cost-effective mobile gate system in engineering designs (or adding one during future maintenance) would improve long-term flood resilience while also preserving and enhancing ecosystem values.

Source: Weinstein, M.P. et al. 2021. Protecting People and Property While Restoring Coastal Wetland Habitats. Estuaries and Coasts. DOI: 10.1007/s12237-021-00900-x

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