Geology topics

Thuy-Vy D. Bui

Publications and source records attributed to Thuy-Vy D. Bui.

6 recordsLinked to original sources

USGS2017

Are coastal managers ready for climate change? A case study from estuaries along the Pacific coast of the United States

A key challenge for coastal resource managers is to plan and implement climate change adaptation strategies inlight of uncertainties and competing management priorities. In 2014, we held six workshops across estuaries along the Pacific coast of North America with over 150 participants to evaluate resource managers' perceived level of understanding of climate change science, where they obtain information, how they use this knowledge, and their preparedness for incorporating climate change into their management decisions. We found that most resource managers understood the types of climate change impacts likely to occur in their estuaries, but often lacked the scientific information to make decisions and plan effectively. Managers stated that time, money, and staff resources were the largest obstacles in their efforts. Managers identified that they learned most of their information from peers, scientific journals, and the Internet and indicated that sea-level rise was their greatest concern. There was, however, variation in managers' levels of readiness and perceived knowledge within and among workshop locations. The workshops revealed that some regions don't have the information they need or the planning capacity to effectively integrate climate change into their management, with eight out of fifteen site comparisons showing a significant difference between their level of preparedness (F 5,26 = 6.852; p = 0.0003), and their willingness to formally plan (F 5,26 = 12.84; p = 0.000002). We found that Urban estuaries were significantly different from Mixed Use and Rural estuaries, in having access to information and feeling more prepared to conduct climate change planning and implementation (F 2,29 = 17.34; p = 0.00001). To facilitate climate change preparedness more comprehensive integration of science into management decisions is essential.

Ocean and Coastal Management↗

USGS2016

A century of landscape disturbance and urbanization of the San Francisco Bay region affects the present-day genetic diversity of the California Ridgway’s rail (Rallus obsoletus obsoletus)

Fragmentation and loss of natural habitat have important consequences for wild populations and can negatively affect long-term viability and resilience to environmental change. Salt marsh obligate species, such as those that occupy the San Francisco Bay Estuary in western North America, occupy already impaired habitats as result of human development and modifications and are highly susceptible to increased habitat loss and fragmentation due to global climate change. We examined the genetic variation of the California Ridgway’s rail ( Rallus obsoletus obsoletus ), a state and federally endangered species that occurs within the fragmented salt marsh of the San Francisco Bay Estuary. We genotyped 107 rails across 11 microsatellite loci and a single mitochondrial gene to estimate genetic diversity and population structure among seven salt marsh fragments and assessed demographic connectivity by inferring patterns of gene flow and migration rates. We found pronounced genetic structuring among four geographically separate genetic clusters across the San Francisco Bay. Gene flow analyses supported a stepping stone model of gene flow from south-to-north. However, contemporary gene flow among the regional embayments was low. Genetic diversity among occupied salt marshes and genetic clusters were not significantly different. We detected low effective population sizes and significantly high relatedness among individuals within salt marshes. Preserving genetic diversity and connectivity throughout the San Francisco Bay may require attention to salt marsh restoration in the Central Bay where habitat is both most limited and most fragmented. Incorporating periodic genetic sampling into the management regime may help evaluate population trends and guide long-term management priorities.

California↗

USGS2016

Endangered species management and ecosystem restoration: Finding the common ground

Management actions to protect endangered species and conserve ecosystem function may not always be in precise alignment. Efforts to recover the California Ridgway’s Rail ( Rallus obsoletus obsoletus ; hereafter, California rail), a federally and state-listed species, and restoration of tidal marsh ecosystems in the San Francisco Bay estuary provide a prime example of habitat restoration that has conflicted with species conservation. On the brink of extinction from habitat loss and degradation, and non-native predators in the 1990s, California rail populations responded positively to introduction of a non-native plant, Atlantic cordgrass ( Spartina alterniflora ). California rail populations were in substantial decline when the non-native Spartina was initially introduced as part of efforts to recover tidal marshes. Subsequent hybridization with the native Pacific cordgrass ( Spartina foliosa ) boosted California rail populations by providing greater cover and increased habitat area. The hybrid cordgrass ( S. alterniflora × S. foliosa ) readily invaded tidal mudflats and channels, and both crowded out native tidal marsh plants and increased sediment accretion in the marsh plain. This resulted in modification of tidal marsh geomorphology, hydrology, productivity, and species composition. Our results show that denser California rail populations occur in invasive Spartina than in native Spartina in San Francisco Bay. Herbicide treatment between 2005 and 2012 removed invasive Spartina from open intertidal mud and preserved foraging habitat for shorebirds. However, removal of invasive Spartina caused substantial decreases in California rail populations. Unknown facets of California rail ecology, undesirable interim stages of tidal marsh restoration, and competing management objectives among stakeholders resulted in management planning for endangered species or ecosystem restoration that favored one goal over the other. We have examined this perceived conflict and propose strategies for moderating harmful effects of restoration while meeting the needs of both endangered species and the imperiled native marsh ecosystem.

California↗

USGS2016

Depredation of the California Ridgway’s rail: Causes and distribution

We studied the causes of mortality for the California Ridgway’s rail at multiple tidal marshes in the San Francisco Bay Estuary, California. We radio-marked 196 individual rails and examined the evidence from 152 recovered California Ridgway’s rail mortalities from our radio-marked sample and determined plausible cause of death from a wide array of evidence. We also included 10 additional California Ridgway’s rail mortalities (unmarked) that we encountered during our normal field operations. We assigned a likely cause of death to 130 of the recoveries, of which 127 were determined to be caused by predation. Of those, 103 could be divided into class of cause (avian or mammalian), and avian predators were responsible for 64% of those events. Primary predators identified include domestic or feral cats, red fox, owl, and northern harrier. We did find seasonal differences between avian and mammalian predation rates, with higher proportions of avian predation in the winter and early spring. Time of day and tide height were correlated with predation events, with a greater proportion of known mortalities found during periods of high tides (over 60% marsh inundation) and during daylight hours. Predation is the primary source of mortality for California Ridgway’s rail. Management actions that try to reduce avian predation may be the most effective at improving rail survival rates, given the proportion of avian predation detected.

Conference Paper↗

USGS2015

Movements of radio-marked California Ridgway's rails during monitoring surveys: Implications for population monitoring

The California Ridgway's rail Rallus obsoletus obsoletus (hereafter California rail) is a secretive marsh bird endemic to tidal marshes in the San Francisco Bay (hereafter bay) of California. The California rail has undergone significant range contraction and population declines due to a variety of factors, including predation and the degradation and loss of habitat. Call-count surveys, which include call playbacks, based on the standardized North American marsh bird monitoring protocol have been conducted throughout the bay since 2005 to monitor population size and distribution of the California rail. However, call-count surveys are difficult to evaluate for efficacy or accuracy. To measure the accuracy of call-count surveys and investigate whether radio-marked California rails moved in response to call-count surveys, we compared locations of radio-marked California rails collected at frequent intervals (15 min) to California rail detections recorded during call-count surveys conducted over the same time periods. Overall, 60% of radio-marked California rails within 200 m of observers were not detected during call-count surveys. Movements of radio-marked California rails showed no directional bias ( P = 0.92) irrespective of whether or not playbacks of five marsh bird species (including the California rail) were broadcast from listening stations. Our findings suggest that playbacks of rail vocalizations do not consistently influence California rail movements during surveys. However, call-count surveys may underestimate California rail presence; therefore, caution should be used when relating raw numbers of call-count detections to population abundance.

Journal of Fish and Wildlife Management↗

USGS2015

Sea-level rise and refuge habitats for tidal marsh species: Can artificial islands save the California Ridgway's rail?

Terrestrial species living in intertidal habitats experience refuge limitation during periods of tidal inundation, which may be exacerbated by seasonal variation in vegetation structure, tidal cycles , and land-use change. Sea-level rise projections indicate the severity of refuge limitation may increase. Artificial habitats that provide escape cover during tidal inundation have been proposed as a temporary solution to alleviate these limitations. We tested for evidence of refuge habitat limitation in a population of endangered California Ridgway's rail ( Rallus obsoletus obsoletus ; hereafter California rail) through use of artificial floating island habitats provided during two winters. Previous studies demonstrated that California rail mortality was especially high during the winter and periods of increased tidal inundation, suggesting that tidal refuge habitat is critical to survival. In our study, California rail regularly used artificial islands during higher tides and daylight hours. When tide levels inundated the marsh plain, use of artificial islands was at least 300 times more frequent than would be expected if California rails used artificial habitats proportional to their availability (0.016%). Probability of use varied among islands, and low levels of use were observed at night. These patterns may result from anti-predator behaviors and heterogeneity in either rail density or availability of natural refuges. Endemic saltmarsh species are increasingly at risk from habitat change resulting from sea-level rise and development of adjacent uplands. Escape cover during tidal inundation may need to be supplemented if species are to survive. Artificial habitats may provide effective short-term mitigation for habitat change and sea-level rise in tidal marsh environments, particularly for conservation-reliant species such as California rails.

California↗