Late-Time Spectroscopy of SN 2002cx: The Prototype of a New Subclass of Type Ia Supernovae

We present Keck optical spectra of SN 2002cx, the most peculiar known Type Ia supernova (SN Ia), taken 227 and 277 days past maximum light. Astonishingly, the spectra are not dominated by the forbidden emission lines of iron that are a hallmark of thermonuclear supernovae in the nebular phase. Instead, we identify numerous P-Cygni profiles of Fe II at very low expansion velocities of about 700 km/s, which are without precedent in SNe Ia. We also report the tentative identification of low-velocity O I in these spectra, suggesting the presence of unburned material near the center of the exploding white dwarf. SN 2002cx is the prototype of a new subclass of SNe Ia, with spectral characteristics that may be consistent with recent pure deflagration models of Chandrasekhar-mass thermonuclear supernovae. These are distinct from the majority of SNe Ia, for which an alternative explosion mechanism, such as a delayed detonation, may be required.Comment: 18 pages, 5 figures, to appear in The Astronomical Journal; minor revisions to match accepted versio

Oyster Demographics in Harvested Reefs vs. No-Take Reserves: Implications for Larval Spillover and Restoration Success

Fishery species that reside in no-take, marine reserves often show striking increases in size and abundance relative to harvested areas, with the potential for larval spillover to harvested populations. The benefits of spillover, however, may not be realized if the populations or habitats outside of reserves are too degraded. We quantified oyster population density and demographics such as recruitment, growth, mortality, and potential larval output as a function of two types of oyster management strategies in Pamlico Sound, North Carolina, USA: (1) natural reefs + harvested and (2) restored reefs + harvested. We compared these data to demographic data collected as a function of a third type of management strategy, (3) restored reefs + protected from harvest. Mean oyster recruitment was ~12 times higher in restored + harvested reefs than in natural + harvested reefs. Mean total oyster density was ~8- to 72-times higher in restored + protected reefs than in restored + harvested or natural + harvested reefs, respectively. Moreover, harvested reefs exhibited truncated size structure, and few or no individuals greater than legal size (75 mm), whereas protected reefs typically had a polymodal size structure, including many large individuals. We estimate that restored + protected reefs have ~4 to 700 times greater potential larval output m−2 than restored + harvested or natural + harvested reefs, respectively. After accounting for total sound-wide areal coverage of each reef type, total potential larval output from restored + protected reefs was ~6 times greater than that from natural + harvested and restored + harvested reefs. Marine reserves can potentially subsidize harvested populations via larval spillover, however, in the case of oyster reefs in Pamlico Sound, the relatively degraded conditions of natural reefs (e.g., low vertical relief, low shell volume per square meter) may not provide much in the way of suitable settlement substrate to realize the benefits of larval spillover from reserves. Restoration of oyster reefs, even with a thin veneer of substrate, may improve settlement substrate to increase the benefits of larval spillover from reserves

Integrating ecosystem services considerations within a GIS-based habitat suitability index for oyster restoration.

Geospatial habitat suitability index (HSI) models have emerged as powerful tools that integrate pertinent spatial information to guide habitat restoration efforts, but have rarely accounted for spatial variation in ecosystem service provision. In this study, we utilized satellite-derived chlorophyll a concentrations for Pamlico Sound, North Carolina, USA in conjunction with data on water flow velocities and dissolved oxygen concentrations to identify potential restoration locations that would maximize the oyster reef-associated ecosystem service of water filtration. We integrated these novel factors associated with oyster water filtration ecosystem services within an existing, 'Metapopulation Persistence' focused GIS-based, HSI model containing biophysical (e.g., salinity, oyster larval connectivity) and logistical (e.g., distance to nearest restoration material stockpile site) factors to identify suitable locations for oyster restoration that maximize long-term persistence of restored oyster populations and water filtration ecosystem service provision. Furthermore, we compared the 'Water Filtration' optimized HSI with the HSI optimized for 'Metapopulation Persistence,' as well as a hybrid model that optimized for both water filtration and metapopulation persistence. Optimal restoration locations (i.e., locations corresponding to the top 1% of suitability scores) were identified that were consistent among the three HSI scenarios (i.e., "win-win" locations), as well as optimal locations unique to a given HSI scenario (i.e., "tradeoff" locations). The modeling framework utilized in this study can provide guidance to restoration practitioners to maximize the cost-efficiency and ecosystem services value of habitat restoration efforts. Furthermore, the functional relationships between oyster water filtration and chlorophyll a concentrations, water flow velocities, and dissolved oxygen applied in this study can guide field- and lab-testing of hypotheses related to optimal conditions for oyster reef restoration to maximize water quality enhancement benefits

Integrating Larval Dispersal, Permitting, and Logistical Factors Within a Validated Habitat Suitability Index for Oyster Restoration

Habitat suitability index (HSI) models are increasingly used to guide ecological restoration. Successful restoration is a byproduct of several factors, including physical and biological processes, as well as permitting and logistical considerations. Rarely are factors from all of these categories included in HSI models, despite their combined relevance to common restoration goals such as population persistence. We developed a Geographic Information System (GIS)-based HSI for restoring persistent high-relief subtidal oyster (Crassostrea virginica) reefs protected from harvest (i.e., sanctuaries) in Pamlico Sound, North Carolina, USA. Expert stakeholder input identified 17 factors to include in the HSI. Factors primarily represented physical (e.g., salinity) and biological (e.g., larval dispersal) processes relevant to oyster restoration, but also included several relevant permitting (e.g., presence of seagrasses) and logistical (e.g., distance to restoration material stockpile sites) considerations. We validated the model with multiple years of oyster density data from existing sanctuaries, and compared HSI output with distributions of oyster reefs from the late 1800's. Of the 17 factors included in the model, stakeholders identified four factors—salinity, larval export from existing oyster sanctuaries, larval import to existing sanctuaries, and dissolved oxygen—most critical to oyster sanctuary site selection. The HSI model provided a quantitative scale over which a vast water body (~6,000 km2) was narrowed down by 95% to a much smaller suite of optimal (top 1% HSI) and suitable (top 5% HSI) locations for oyster restoration. Optimal and suitable restoration locations were clustered in northeast and southwest Pamlico Sound. Oyster density in existing sanctuaries, normalized for time since reef restoration, was a positive exponential function of HSI, providing validation for the model. Only a small portion (10–20%) of historical reef locations overlapped with current, model-predicted optimal and suitable restoration habitat. We contend that stronger linkages between larval connectivity, landscape ecology, stakeholder engagement and spatial planning within HSI models can provide a more holistic, unified approach to restoration

Oyster IPM w/Positive Feedbacks - Code

Code used in: Moore, J.L., Puckett, B., and Schreiber, S.J. Restoration of Eastern oyster populations with positive density dependence. Submitted to Ecological Applications July 2017

Oyster IPM w/Positive Feedbacks - Metadata

Description of data and code used in: Moore, J.L., Puckett, B., and Schreiber, S.J. Restoration of Eastern oyster populations with positive density dependence. Submitted to Ecological Applications December 2017

Oyster IPM w/Positive Feedbacks - Data

Data used in: Moore, J.L., Puckett, B., and Schreiber, S.J. Restoration of Eastern oyster populations with positive density dependence. Submitted to Ecological Applications December 2017

Density-dependent role of an invasive marsh grass, <i>Phragmites australis</i>, on ecosystem service provision

<div><p>Invasive species can positively, neutrally, or negatively affect the provision of ecosystem services. The direction and magnitude of this effect can be a function of the invaders’ density and the service(s) of interest. We assessed the density-dependent effect of an invasive marsh grass, <i>Phragmites australis</i>, on three ecosystem services (plant diversity and community structure, shoreline stabilization, and carbon storage) in two oligohaline marshes within the North Carolina Coastal Reserve and National Estuarine Research Reserve System (NCNERR), USA. Plant species richness was equivalent among low, medium and high <i>Phragmites</i> density plots, and overall plant community composition did not vary significantly by <i>Phragmites</i> density. Shoreline change was most negative (landward retreat) where <i>Phragmites</i> density was highest (-0.40 ± 0.19 m yr^-1 vs. -0.31 ± 0.10 for low density <i>Phragmites</i>) in the high energy marsh of Kitty Hawk Woods Reserve and most positive (soundward advance) where <i>Phragmites</i> density was highest (0.19 ± 0.05 m yr^-1 vs. 0.12 ± 0.07 for low density <i>Phragmites</i>) in the lower energy marsh of Currituck Banks Reserve, although there was no significant effect of <i>Phragmites</i> density on shoreline change. In Currituck Banks, mean soil carbon content was approximately equivalent in cores extracted from low and high <i>Phragmites</i> density plots (23.23 ± 2.0 kg C m^-3 vs. 22.81 ± 3.8). In Kitty Hawk Woods, mean soil carbon content was greater in low <i>Phragmites</i> density plots (36.63 ± 10.22 kg C m^-3) than those with medium (13.99 ± 1.23 kg C m^-3) or high density (21.61 ± 4.53 kg C m^-3), but differences were not significant. These findings suggest an overall neutral density-dependent effect of <i>Phragmites</i> on three ecosystem services within two oligohaline marshes in different environmental settings within a protected reserve system. Moreover, the conceptual framework of this study can broadly inform an ecosystem services-based approach to invasive species management.</p></div

Sampling locations.

<p>A) Location of Currituck Banks and Kitty Hawk Woods Reserves (stars), components of the North Carolina Coastal Reserve and National Estuarine Research Reserve system, in Currituck Sound, North Carolina, USA. B) Location of sampled Low, Medium, and High <i>Phragmites</i> Density sites (stars) within Kitty Hawk Woods Reserve. C) Location of sampled Low and High <i>Phragmites</i> Density sites (stars) within Currituck Banks Reserve—note that no Medium <i>Phragmites</i> density sites were present within Currituck Banks Reserve. All satellite imagery was derived from United States Geological Survey, High Resolution Orthoimagery Dataset.</p