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Coastal & Estuarine Science News (CESN)

Coastal & Estuarine Science News (CESN) is an electronic publication providing brief summaries of select articles from the journal Estuaries & 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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2017 November

Contents

Healthy Oyster Reefs, Healthy Sediment
Bulkheads No Good for Birds
Bad News for Bay’s Aquatic Vegetation
Open the Gates for Fish


Healthy Oyster Reefs, Healthy Sediment

Restored oyster reefs rapidly become biogeochemical hotspots

Managers worldwide are interested in the restoration of oyster reefs, not only for their direct benefit in terms of human food but also for the ecosystem services they provide. But while we know a lot about how healthy intertidal oyster reefs benefit water quality, their effects on the biogeochemical processes of the seabed—the chemical properties of sediments, nutrient cycling, and the activity of microbes—is less well-studied. A new study tackles this question and reveals that restored reefs quickly become biogeochemical hotspots.

Researchers collected sediment cores from dead reefs, natural reefs, and one-, four-, and seven-year-old restored reefs in Florida’s Canaveral National Seashore, part of Mosquito Lagoon in the northern Indian River Lagoon, where a community-based effort has restored 77 patch reefs since 2007. Their analysis showed that the presence of live oysters, whether on a restored or natural reef, significantly decreased sediment bulk density and increased the concentration of several key nutrients. The activity of microbial enzymes involved in carbon, nitrogen, and phosphorous cycling also increased. These effects became apparent within a single year of a reef’s restoration and remained fairly stable as reefs aged, making restored reefs key hotspots for nutrient cycling.

Even among reefs of the same type and age, however, these characteristics sometimes varied significantly. The researchers suggested that this was due to variability in oyster recruitment and/or reef thickness, which can be affected by oyster harvesting. If factors such as harvesting can affect outcomes, then the task of managing the biogeochemical processes in oyster reef sediments doesn’t end with restoration—monitoring will also be an important part of for assessing whether restoration efforts are successful.

Source: Chambers, L.G., S.A. Gaspar, C.J. Pilato, H.E. Steinmuller, K.J. McCarthy, P.E. Sacks, and L.J. Walters. 2017. How Well Do Restored Intertidal Oyster Reefs Support Key Biogeochemical Properties in a Coastal Lagoon?. Estuaries and Coasts. DOI: 10.1007/s12237-017-0311-5

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Bulkheads No Good for Birds

Shoreline hardening decreases waterbird community integrity

Shoreline hardening through the construction of bulkheads and other structures is a common practice to protect coastal homes, businesses, and infrastructure. Although a number of studies have documented changes in the marine life of estuaries and bays with hardened shorelines, few have examined their effects on waterbirds. A new study used an index of waterbird community integrity (IWCI) to evaluate this based on the sensitivity of different bird species, such as ducks, wading birds, and shorebirds, to anthropogenic disturbance.

The study consisted of waterbird surveys in 21 sub-estuaries in the Chesapeake Bay over the course of 5 years, done in both late summer (post-breeding) and late fall (migrating and wintering) to capture different populations. The researchers looked at effects of factors at three scales—local shoreline type, land use in local sub-estuary up to 500 meters inland, and watershed-scale land use more than 500 meters from the shoreline. They found significant negative relationships between the extent of hardened shoreline and the IWCI in both seasons. The best statistical model based on the data showed significant factors only at the local scale: the percentage of shoreline bulkhead in both summer and fall, and the percentage of Phragmites-dominated shoreline in fall. The effects likely resulted from deeper water and reduced prey availability.

The pressure to expand shoreline armoring in response to rising sea levels does not bode well for the future of waterbirds in coastal regions. However, the researchers see potential in preliminary research on “living shorelines,” which incorporate vegetation and natural materials and keep many ecological functions intact. Although more research is needed on their ability to support waterbird communities, living shorelines may be able to mitigate many of the negative impacts of traditional shoreline armoring.

Source: Prosser, D.J., J.L. Nagel, S. Howlin, P.R. Marbán, D.D. Day, and R.M. Erwin. 2017. Effects of Local Shoreline and Subestuary Watershed Condition on Waterbird Community Integrity: Influences of Geospatial Scale and Season in the Chesapeake Bay. Estuaries and Coasts. DOI: 10.1007/s12237-017-0288-0

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Bad News for Bay’s Aquatic Vegetation

Shoreline hardening negatively affects health and resilience of SAV habitat

Submerged aquatic vegetation, or SAV, provides a wide range of ecosystem services in estuarine waters, from supporting an array of economically important species to sequestering carbon. Coastal development, which tends to decrease water clarity, is seen as the most important threat to healthy SAV communities, but shoreline hardening structures such as riprap are increasingly recognized as a direct hazard as well. New research has documented this effect on the Mid-Atlantic Coast.

The authors of the study surveyed 24 estuarine sites in the Chesapeake and Mid-Atlantic Coastal Bays with a diverse range of salinities and land use types, comparing SAV adjacent to natural shorelines with that adjacent to riprap-hardened shorelines. They found that species diversity, species evenness, and percent cover—all characteristics associated with habitat quality and resilience—were significantly lower where riprap was present. Long-term monitoring of a subset of sites also showed that SAV adjacent to natural shorelines was able to recover faster from the effects of severe storms.

The region’s growing population, along with worsening coastal flooding due to climate change, are likely to further accelerate the use of shoreline hardening and put SAV in the area at greater risk. According to the study’s authors, some of the stress put on SAV by riprap could be mitigated by improving water quality and clarity. It will also be crucial to maintain natural shorelines and forested watersheds and to restore armored shorelines to a natural state wherever possible, which will facilitate natural coastal retreat as sea level rise continues.

Source: Landry, J.B., and R.R. Golden. 2017. In Situ Effects of Shoreline Type and Watershed Land Use on Submerged Aquatic Vegetation Habitat Quality in the Chesapeake and Mid-Atlantic Coastal Bays. Estuaries and Coasts. DOI: 10.1007/s12237-017-0316-0

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Open the Gates for Fish

Floodgate operations affect fish communities

Floodgates help prevent the flooding of coastal areas by regulating the flow of water between river mainstems and tidal creeks. However, they can influence fish communities by physically restricting fish passage and altering upstream water quality. These types of changes have been documented worldwide, but few studies have examined how specific floodgate operation practices influence fish communities—until now.

A new study from the lower Fraser River region in British Columbia, which is home to over 2.7 million people and over 400 floodgates, used time-lapse photography to monitor how often 18 floodgates were open. Researchers sampled fish above and below the floodgates in late summer and measured the water’s dissolved oxygen, salinity, conductivity, and temperature, as well as collecting the same data from four floodgate-free tidal creeks for comparison.

The less time a floodgate spent open, the greater the differences between the upstream and downstream fish communities. Reductions in time open were also correlated with fewer native species and lower dissolved oxygen concentrations upstream. Some species, such as the prickly sculpin, seemed more sensitive to floodgate operations than others.

This study demonstrates that it should be possible to modify floodgate operations to minimize their negative impacts—particularly by increasing how much time floodgates spend open, especially in systems in which they are currently open only rarely. The Lower Fraser region is currently undergoing a strategic flood management planning processes due to aging infrastructure and increasing flood risk due to sea level rise, and these results can contribute to the development of a new management plan that takes these results into account.

Source: Seifert, R.E., and J.W. Moore. 2017. Floodgate Operations and Fish Communities in Tidal Creeks of the Lower Fraser River (British Columbia, Canada). Estuaries and Coasts. DOI: 10.1007/s12237-017-0313-3

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