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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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October 2021

Table of Contents

Culverts Alter Habitats in an Urbanized Setting
The differences between a tidal bay and an adjacent lagoon

Structures like culverts can provide hydrologic control in wetlands—facilitating road crossings, boat navigation, flood control, and waterfowl management—but they also create barriers that may increase patchiness among previously interconnected habitats. To better understand the potential impacts of these hydrologic manipulations, researchers compared habitat conditions between a tidally restricted urban lagoon and a large, heavily utilized tidal bay—Los Angeles County’s Colorado Lagoon and Alamitos Bay—which are connected by a 268-meter-long concrete box culvert that was constructed in the 1960s. The team analyzed abiotic conditions including water chemistry and sediment characteristics as well as the abundance, species richness, and diversity of the biotic communities on both sides of the barrier.

Their results indicate that the presence of the culvert changes conditions in the lagoon by dampening the tidal amplitude, restricting flow, and acting as a barrier for the movements of organisms. The lagoon had more extreme temperature differences, decreased dissolved oxygen and salinity, and lower zooplankton abundance than the bay. The composition of the zooplankton, benthic macroinvertebrate, and small fish communities also differed between the two sites, suggesting limited habitat connectivity despite their proximity.

Restoration efforts since 2009 have significantly improved conditions in the lagoon by rerouting storm water runoff, removing contaminated sediment, clearing debris within the culvert, and restoring native salt marsh and coastal sage scrub plant communities. The next phase of restoration will include removing the culvert and restoring full tidal influence. This will create an open water channel, which the study authors anticipate will decrease fragmentation and habitat heterogeneity, such that the faunal communities will once again be interconnected.

Source: Burdick-Whipp, M.K. et al. 2021. Understanding Habitat Fragmentation Between a Full Tidal Bay and a Tidally Restricted Urban Lagoon. Estuaries and Coasts. DOI: 10.1007/s12237-021-00948-9


Fluid Look at Estuarine Aquatic Habitat

SAV distribution in the Gulf of Mexico

Submerged aquatic vegetation can occur along the entire estuarine salinity gradient, where it provides critical habitat for many fish and wildlife species. Although many programs use emergent marsh vegetation to classify habitat zones in estuaries, SAV distribution can provide added insight into environmental conditions.

Researchers working in the northern Gulf of Mexico compiled information on water quality and SAV species assemblages and biomass at 384 sites across the entire salinity gradient in estuaries that occurred between Alabama’s Mobile Bay and San Antonio Bay in Texas. They found a total of 15 species, with the highest biomass in fresh areas. Although there was some evidence for shifts over time, coast-wide SAV occurrence and biomass were remarkably consistent over the three years of study, with SAV covering approximately 16% of the bottom and supporting an average of 25 grams of biomass per meter squared.

Cluster analysis of these results showed that particular combinations of salinity, turbidity, and depth were associated with unique SAV assemblages—which may be the result of differences in hydrology (due to precipitation, freshwater input, and water depth) and exposure (due to wave and wind energy). Because emergent wetland communities may be slower to shift than SAV, marsh zone classifications based on emergent vegetation do not fully capture these types of differences. The researchers suggest that SAV distributions could be used to develop aquatic habitat zones that are sensitive to environmental change and can be used to inform ecosystem-based assessments and restoration plans.

Source: DeMarco, K.E. et al. 2021. Defining Aquatic Habitat Zones Across Northern Gulf of Mexico Estuarine Gradients Through Submerged Aquatic Vegetation Species Assemblage and Biomass Data. Estuaries and Coasts. DOI: 10.1007/s12237-021-00958-7

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Making Conservation Choices
Decision analysis can help clarify trade-offs in coastal resilience objectives

Prioritizing investments in coastal resilience can be challenging, given limited time and money and potential conflicts between achieving ecological and socioeconomic goals. It would be useful to have an approach that makes the decision process transparent and allows managers to see trade-offs when optimizing multiple objectives.

Using decision analysis, researchers from The Nature Conservancy evaluated conservation planning units across Maryland’s Lower Eastern Shore, an area where sea-level rise threatens both intertidal wetlands and some of the state’s poorest communities. Their two objectives were to minimize habitat loss in the wetlands and reduce flood impacts on communities. The area was divided into seven planning units (one bay and six peninsula communities) that contain important ecological and cultural heritage areas. The team identified a series of relevant attributes for each objective, including the presence of focal species and migration space as metrics to consider for habitat protection and the presence of flood-prone areas and critical infrastructure for flooding impacts. Attribute information was then combined into an overall value for each objective, which could be compared across units.

The seven units had a range of scores, highlighting clear trade-offs between habitat and flood protection. The unit that ranked the highest in terms of minimizing community flood impacts, for example, did not fare as well in terms of minimizing habitat loss. Seeing it laid out this way allowed the team to identify the units that did fairly well with both objectives, making these high priorities for conservation investment. For example, the analysis was helpful for making a determination regarding the purchase of a conservation easement.

This approach increases transparency in decision-making and makes assumptions explicit using value-based data. Knowing how results are derived and the trade-offs among objectives provides a useful framework for making informed conservation decisions.

Source: Martin, D.M. et al. 2021. Using Decision Analysis to Integrate Habitat and Community Values for Coastal Resilience Planning. Estuaries and Coasts. DOI: 10.1007/s12237-021-00970-x

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Water Quality in Tidal Creeks
An open science dashboard in southwest Florida

Despite the abundance of tidal creeks and their key role as pathways for nutrients, water quality in these tributaries is not as well understood in comparison to larger estuaries. Part of this is due to limited information on creek condition, making it difficult to identify which creeks are in need of management actions. To address this data deficit, researchers worked with three contiguous National Estuary Programs along the Gulf Coast of Florida to develop a tidal creek water quality assessment framework for the region. This enabled them to create a report card on tidal creek health and prioritize creeks for additional action.  

The framework includes commonly collected water quality and creek attribute data from a variety of available sources including the USDA, hydrography datasets, and watershed loading models. To this baseline, the team added their own measurements sampled from 16 tidal creeks between Tampa and Estero bays. The information was used to develop indicators of creek condition and to classify each creek as No Data, Monitor, Caution, Investigate, or Prioritize. A host of plots show the relationships between the various categories of data in order to offer water managers a snapshot of each creek’s health.

The data used for this assessment are displayed online in an openly available, continually updated tidal creeks dashboard. This screening and prioritization tool allows managers to identify potential problem areas and see which creeks should be targeted for intervention. The value of the report card was highlighted even when data were limited. For example, one creek was placed in the “Investigate” category based on only four samples from a historical database, triggering follow-up with local resource managers, who identified additional data that had not been included in the statewide data repository. This type of project demonstrates the value of open science.

Source: Wessel, M.R. et al. 2021. Developing a Water Quality Assessment Framework for Southwest Florida Tidal Creeks. Estuaries and Coasts. DOI: 10.1007/s12237-021-00974-7

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