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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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March 2020

Table of Contents

The End of "Statistical Significance"?
It's Complicated: Constructed Oyster Reefs and Wave Height
Not Too Shallow, Not Too Deep: Helping Seagrass to Shine
A Regional Model for Wetlands Restoration

The End of "Statistical Significance"?
An analysis of scientific reliance on p-values

In most peer-reviewed scientific publications, findings are considered sound if researchers can demonstrate “statistical significance” by showing that a probability value – referred to as the p-value – for their data is above a certain threshold. Yet in recent years, researchers have begun to question the value of the p-value, with the American Statistical Association and many others weighing in on the subject. In a perspective paper, statistician Eric Smith examined this ongoing debate by reviewing papers in Estuaries and Coasts to evaluate whether authors show an over-reliance on the use of statistical significance.

Smith makes a series of recommendations for authors, reviewers, and publishers seeking to judge and improve research publications. These recommendations range from avoiding the use of the term “statistical significance” altogether to providing p-values with more precision – up to three or four digits. For reviewers and editors, he suggests discontinuing the practice of evaluating conclusions solely on the basis of p-value.
Overall, the paper makes a compelling case that researchers should have a more consistent framework for reporting quantitative evidence, without necessarily eliminating inferential statistics altogether. For those who rely on sound science to inform their decision-making, this perspective article is worth a look.

Source: Smith, E.P. 2019. Ending Reliance on Statistical Significance Will Improve Environmental Inference and Communication. Estuaries and Coasts. DOI: 10.1007/s12237-019-00679-y

It's Complicated: Constructed Oyster Reefs and Wave Height
Reefs can both reduce and amplify waves

Constructed oyster reefs are increasingly considered as a potential natural way to protect shorelines from wind waves and swell. But do these reefs always help? A two-month study in the upper Delaware Bay produced results that suggest the protection offered by constructed oyster reefs (CORs) is not so straightforward.

The study deployed wave sensors on both the landward and seaward side of a segmented COR, measuring wave energy over the course of two months in 2018 – including during four nor’easters. To their surprise, the researchers found that the reefs reduce wave height under some conditions, but can amplify wave height under others. And although emergent reefs (those that are above water during some parts of the tide) blocked wind waves, swell energy could transmit through CORs without dampening, regardless of the reef’s height.

The authors found that wave attenuation across constructed oyster reefs depended on a number of factors, including the configuration of the reef, the wave environment (i.e., dominated by swells vs. by wind waves), and local bathymetry – which, in the upper Delaware Bay, is complicated. Indeed, complicated seems to be the word of choice for the relationship between oyster reefs and waves. In contrast to this study, which was conducted in a high-energy environment, a different study we highlighted in 2019 showed how oyster reefs can significantly affect wave attenuation in a low-energy environment.  

Source: Zhu, L. et al. 2020. Field Observations of Wind Waves in Upper Delaware Bay with Living Shorelines. Estuaries and Coasts. DOI: 10.1007/s12237-019-00670-7

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Not Too Shallow, Not Too Deep: Helping Seagrass to Shine
Knowing where to plant seagrass makes for smarter restoration

Seagrass meadows are beneficial ecosystems that clarify water, provide habitat, and help to protect the shoreline. But globally, about a third of historic seagrass meadows have been lost since the late 1800s, with losses accelerating through the end of the 20th century.

To determine the best conditions for seagrass rehabilitation, a team of researchers seeded eelgrass (Zostera marina) in Virginia’s Hog Island Bay in 2006 and monitored shoot densities for 12 years. Eelgrass seeds were placed at varying densities in plots of different sizes at water depths ranging from 0.8 to 1.6 meters. A seagrass die-off occurred in July 2012 due to a severe heat wave, allowing the researchers to track long-term recovery from a high-temperature disturbance as part of the project.

The study found that planting depth, and its interaction with light and water temperature, was the key factor in seagrass success and resilience: At depths greater than 1.4 meters, sediment suspended by wind and waves blocked out the light, whereas at shallow depths of a meter or less, plants were damaged by warm water temperatures of 28 degrees Celsius or higher. In these coastal bays, the sweet spot occurred at depths of 1.0 to 1.3 meters.

Marine heat waves of sustained elevated temperatures are becoming an increasingly common phenomenon, and sea level rise affects the distribution of habitable areas. Both of these factors have the potential to affect seagrass. The good news here is that seagrass densities in more than a third of the restoration plots have now recovered. So by considering depth, managers can better identify areas likely to be resilient – which could ultimately help improve water quality and provide a bulwark against future climate-driven impacts.

Source: Aoki, L.R. et al. 2020. Depth Affects Seagrass Restoration Success and Resilience to Marine Heat Wave Disturbance. Estuaries and Coasts. DOI: 10.1007/s12237-019-00685-0

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A Regional Model for Wetlands Restoration
Categorizing wetlands can facilitate analysis

Restoring individual wetlands in the face of complex landscape-level stressors like sea level rise is a daunting task, especially since estuaries and coastal wetlands come in all sorts of shapes, sizes, and background stories. A recent study shows that grouping wetlands by type and synthesizing information across larger regions can help to prioritize restoration actions.

To help develop regional recommendations to guide restoration for the next several decades, researchers in California examined wetlands along the Southern California Bight, from Point Conception to Mexico. The team grouped 105 individual wetlands – down from 331 in 1850 – into seven categories based on characteristics like size, the estuary’s history of fragmentation, and how often the system is flushed by tides. The researchers applied a simple model to evaluate how changes in sea level, accretion of sediments, and estuary mouth dynamics would affect each wetland and summed it for the region. When data didn’t exist for a particular system, they were able to substitute information from others in the same category.

They found that sea level rise affected different wetland types differently, with large losses of vegetated area predicted for lagoons and fragmented river valley estuaries. The model showed that facilitating wetland migration into undeveloped areas will offset vegetated wetland losses to some extent, and that gains from additional management actions – such as reconnecting fragmented systems – could result in a net positive.

Many coastal regions have a diversity of small to medium-sized wetlands, and this study shows the value of generalizing across different categories and managing for a mix of wetlands types across a whole region.

Source: Stein, E.D. et al. 2019. Establishing Targets for Regional Coastal Wetland Restoration 
Planning Using Historical Ecology and Future Scenario Analysis: The Past, Present, Future Approach.
Estuaries and Coasts. DOI: 10.1007/s12237-019-00681-4

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