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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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2020 November

Table of Contents

Derelict Crab Traps Continue to Kill for Years
How Plants Influence the Resilience of Wetlands to Sea Level Rise
10 Questions to Ask About the Future of Tidal Marshes
A New Technique for Mapping Hard-Bottom Habits


Derelict Crab Traps Continue to Kill for Years
The benefits of removing unused traps from the Gulf of Mexico

Despite being abandoned or lost in a storm, derelict fishing gear continues to catch wildlife in a process known as ghost fishing. Blue crab traps made of galvanized metal or vinyl-coated wire can capture and kill crabs and finfish alike for more than a year (three years in some cases). To calculate the benefits of trap removal, researchers used published data and fishery surveys to estimate ghost fishing mortality rates in the Gulf of Mexico. Based on this analysis, 25 percent of traps—for a total of 223,000—are lost every year across 28 shallow, estuarine waterbodies in five states, with the highest numbers and densities found in Louisiana. The team estimated mortality rates at about 26 crabs and 8 fish per trap per year.

According to their results, a Gulf-wide removal program targeting just 10 percent of derelict traps would save 391,000 kilograms of crabs and 300,000 kilograms of finfish over the course of five years. If all of the captured blue crabs were harvestable, that biomass would be valued at more than $978,000 in Louisiana alone based on 2016 prices. Removing traps could also offer additional benefits: reducing entanglement hazards for marine wildlife and the smothering of seagrass habitats and coral reefs, improving beach aesthetics, and potentially increasing harvestable catches.

Funding is currently available to address trap removal as part of ongoing efforts to restore the Gulf of Mexico after the Deepwater Horizon incident, and the model developed in this analysis could help managers locate and target hotspots that would benefit most from removal programs. Fishery managers could use similar methods to calculate the benefits of other options that lessen the impact of derelict traps, such as requiring degradable panels that allow trapped organisms to escape unharmed.

Source: Arthur, C. et al. 2020. Estimating the Benefits of Derelict Crab Trap Removal in the Gulf of Mexico. Estuaries and Coasts. DOI: 10.1007/s12237-020-00812-2

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How Plants Influence the Resilience of Wetlands to Sea Level Rise
Salt marshes and mangrove forests trap sediment and contribute organic matter

To keep pace with sea level rise, coastal wetlands must maintain sufficient elevation by accumulating sediment and fostering the upward expansion of the soil surface. Plants, in addition to physical processes, play a key role in how wetlands maintain this optimum vertical position and should be factored into predictions about the vulnerability—or resilience—of coastal wetlands.

A team of researchers synthesized recent studies on how plants in salt marshes and mangrove forests influence both biological and physical processes including sediment accretion, elevation adjustments, and compaction or erosion of deposited material. Although they occupy different latitudes, the plants in both habitats stabilize emergent mudflats as they become vegetated wetlands. They help to sustain their position relative to sea level by controlling soil elevation in three ways. First, plants contribute belowground biomass in the form of roots, rhizomes, and shoot bases. Second, they trap and retain mineral sediment by slowing down water flow and reducing turbulence. Finally, although less understood, plants also increase soil shear strength by binding sediment in root masses, thereby reducing compaction and erosion.

Salt marshes and mangroves occur along a continuum from sediment-rich to sediment-lacking environments, so each setting will require a different management approach. Habitat stability in settings with high sediment supply can be maintained by sustaining mineral sedimentation. In these environments, such as Brant Pass at the mouth of the Mississippi River, plants can enhance sediment retention by approximately 10 percent. Conversely, systems with little or no mineral sediment available will benefit from focusing more on vegetation health. For example, Twin Cays in Belize is a mangrove ecosystem that has kept pace with the rising seas for millennia through the accumulation of organic matter.

Source: Cahoon, D.R. et al. 2020. How Plants Influence Resilience of Salt Marsh and Mangrove Wetlands to Sea-Level Rise. Estuaries and Coasts. DOI: 10.1007/s12237-020-00834-w

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10 Questions to Ask About the Future of Tidal Marshes
How does the combination of climate change and urbanization affect marsh function?

The capacity of tidal marshes to support important ecosystem services—such as providing fisheries habitat, carbon sequestration, and shoreline protection—is increasingly jeopardized by human actions. Climate change causes species redistribution, alters weather patterns, and increases the risk of coastal erosion through sea level rise. At the same time, the effects of urbanization—habitat loss, eutrophication, overfishing, and the spread of invasive species—interact with each other and with climate change to alter the structure and function of tidal marshes on local and global scales, and across temporal scales too. However, research into the full effects of these multi-scaled, interacting stressors on tidal marshes is just beginning.

A large interdisciplinary team of researchers identified key knowledge gaps and posed 10 priority research questions that should be addressed to understand the consequences of human actions on tidal marshes.

  1. How will climate change and variability affect ecological functions?
  2. What is the impact of climate change on species distribution?
  3. What effect will invasive species have?
  4. What controls the impacts of nutrient loading?
  5. How does urbanization change ecosystems around tidal marshes?
  6. How do changes in tidal marsh composition affect ecological functions?
  7. How will the long-term storage of carbon in tidal marshes change?
  8. How will climate change interact with local stressors to modify food webs and fisheries?
  9. What restoration designs will optimize ecological functions and ecosystem services?
  10. How will human impacts affect the capacity for nutrient sequestration?

There is a clear link between anthropogenic impacts, the condition and extent of tidal marshes, and their capacity to deliver key ecosystem services. To optimize interventions, we need accurate predictions about the effects of a combination of these factors at both the habitat and seascape scales.  

Source: Gilby, B.L. et al. 2020. Human Actions Alter Tidal Marsh Seascapes and the Provision of Ecosystem Services. Estuaries and Coasts. DOI: 10.1007/s12237-020-00830-0

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A New Technique for Mapping Hard-Bottom Habitats
Mapping glacial moraine deposits aids in studying the effects of offshore wind farms

Offshore wind farms are a rapidly growing component of ocean infrastructure, which may affect the connectivity of marine populations by altering both biological communities and sedimentary environments. Several projects are underway along the Atlantic coast in areas encompassing glacial moraine deposits—structurally complex, hard-bottom habitats that are critical to ecologically and economically important species including the American lobster. However, most seafloor-sampling devices and assessment techniques were developed for soft-sediment environments.

To detect and document the effects of wind farms and their related anchoring activity on hard-bottom habitats, researchers combined underwater video and still imagery with high-resolution acoustic geophysical data. They developed and tested their approach at the Block Island Wind Farm off Rhode Island. Its southernmost wind turbine generator is located near one of several shallow ridges formed by glacial moraine deposits. The team conducted surveys before and after construction, assembling baseline data on abiotic and biotic habitat features in order to detect anchoring disturbance.

The diverse habitats near the wind farm range from rippled, gravelly sand with sparse biotic cover to nearly continuous fields of cobbles and boulders supporting diverse and abundant life. In habitats with mixed, patchy topography, the team detected evidence of anchoring disturbance as a result of the initial installation—parallel lines, or furrows, three to five meters across, 32 to 145 meters long. However, recolonization from nearby communities was swift: Although anchor marks remain, the biotic cover of anchor furrows resembled nearby habitats within a year.

The large, seascape scale provided by the geophysical data allowed the team to then target hard-bottom areas of impact for sampling with cameras. This type of multi-scale approach will help assess benthic habitats for offshore wind development plans and environmental studies, particularly in New England where moraine habitats are found.

Source: Guarinello, M.L. and D.A. Carey. 2020. Multi-modal Approach for Benthic Impact Assessments in Moraine Habitats: a Case Study at the Block Island Wind Farm. Estuaries and Coasts. DOI: 10.1007/s12237-020-00818-w

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