Aggregational behavior of the blue mussels Mytilus edulis and Mytilus trossulus: a potential pre‐zygotic reproductive isolation mechanism

The blue mussels Mytilus edulis and Mytilus trossulus occur sympatrically and are able to hybridize in populations on the eastern coast of Newfoundland, Canada, presenting an opportunity to study their aggregational behavior. Aggregation behavior may therefore provide insight into post‐settlement interactions and pre‐zygotic reproductive isolation between the species. Three treatments were designed using M. edulis and M. trossulus to investigate their intraspecific and interspecific spatial distribution patterns. With Ripley’s K‐function and Monte Carlo simulation analysis, we found that in the single‐species treatment, M. edulis aggregated significantly but not M. trossulus. Based on results of two‐way ANOVAs, both the number of aggregations and the moving distance were significantly affected by the treatments (single‐species or mixed‐species treatment) and times (24, 48, 72 and 96 h). In further pairwise comparisons using Tukey’s test, M. edulis aggregated differently with or without M. trossulus occupying the same tank, suggesting that the aggregational behavior of M. edulis could be driven by species‐specific chemical cues. The result that M. edulis aggregates intraspecifically may increase the probability of intraspecific fertilization of the spawned gametes and thus function as a pre‐zygotic reproductive isolation mechanism maintaining the blue mussel hybrid zone.     

Alternating Gaussian process modulated renewal processes for modeling threshold exceedances and durations

It is often of interest to model the incidence and duration of threshold exceedance events for an environmental variable over a set of monitoring locations. Such data arrive over continuous time and can be considered as observations of a two-state process yielding, sequentially, a length of time in the below threshold state followed by a length of time in the above threshold state, then returning to the below threshold state, etc. We have a two-state continuous time Markov process, often referred to as an alternating renewal process. The process is observed over a truncated time window and, within this window, duration in each state is modeled using a distinct cumulative intensity specification. Initially, we model each intensity over the window using a parametric regression specification. We extend the regression specification adding temporal random effects to enrich the model using a realization of a log Gaussian process over time. With only one type of renewal, this specification is referred to as a Gaussian process modulated renewal process. Here, we introduce Gaussian process modulation to the intensity for each state. Model fitting is done within a Bayesian framework. We clarify that fitting with a customary log Gaussian process specification over a lengthy time window is computationally infeasible. The nearest neighbor Gaussian process, which supplies sparse covariance structure, is adopted to enable tractable computation. We propose methods for both generating data under our models and for conducting model comparison. The model is applied to hourly ozone data for four monitoring sites at different locations across the United States for the ozone season of 2014. For each site, we obtain estimated profiles of up-crossing and down-crossing intensity functions through time. In addition, we obtain inference regarding the number of exceedances, the distribution of the duration of exceedance events, and the proportion of time in the above and below threshold state for any time interval.     

Between Environmental Change and Neoliberalism: The Effects of Oil Palm Production on Livelihood Resilience

Rural communities worldwide are increasingly confronted with the simultaneous impacts of environmental change dynamics and processes of economic restructuring that diminish traditional sources of state support while shifting investments toward large-scale intensive production models. A key question in this context is how livelihoods are affected by these interacting forces of change and whether new production models can contribute to resilience at the household and community scales. Here we examine the impacts of oil palm production on marginal rural communities in Mexico that have experienced both the economic changes associated with neoliberal policy reforms and the dynamics of environmental change. We find that oil palm production can contribute to livelihood resilience when community members participate in its management and governance and when production is associated with state support, but that the kinds of neoliberal policies promoting oil palm expansion may exacerbate existing community vulnerabilities in the face of environmental change.     

Mechanisms of ringwoodite formation in shocked meteorites: Evidence from L5 chondrite Dhofar 1970

The formation of the high‐pressure compositional equivalents of olivine and pyroxene has been well‐documented within and surrounding shock‐induced veins in chondritic meteorites, formed by crystallization from a liquid‐ or solid‐state phase transformation. Typically polycrystalline ringwoodite grains have a narrow range of compositions that overlap with those of their olivine precursors, whereas the formation of iron‐enriched ringwoodite has been documented from only a handful of meteorites. Here, we report backscattered electron images, quantitative wavelength‐dispersive spectrometry (WDS) analyses, qualitative WDS elemental X‐ray maps, and micro‐Raman spectra that reveal the presence of Fe‐rich ringwoodite (Fa_44‐63) as fine‐grained (500 nm), polycrystalline rims on olivine (Fa_24‐25) wall rock and as clasts engulfed by shock melt in a previously unstudied L5 chondrite, Dhofar 1970. Crystallization of majorite + magnesiowüstite in the vein interior and metastable mineral assemblages within 35 μm of the vein margin attest to rapid crystallization of a superheated shock melt (>2300 K) from 20─25 GPa to ambient pressure and temperature. The texture and composition of bright polycrystalline ringwoodite rims (Fa_44‐63; MnO 0.01─0.08 wt%) surrounding dark polycrystalline olivine (Fa_8‐14; MnO 0.56─0.65 wt%) implies a solid‐state transformation mechanism in which Fe was preferentially partitioned to ringwoodite. The spatial association between ringwoodite and shock melt suggests that the rapidly fluctuating thermal regimes experienced by chondritic minerals in contact with shock melt are necessary to both drive phase transformation but also to prevent back‐transformation.     

The influence of vegetation cover on evapotranspiration atop waste rock piles,Elk Valley,British Columbia

Surface mining in the Elk Valley, British Columbia, involves removing vegetation, soil, and rock to access underlying metallurgical coal. Subsequent waste rock is placed into adjacent valleys, frequently burying headwater streams. Due to their coarse texture, waste rock piles increase infiltration and percolation, increasing solute transport and concentration of geochemicals in downstream surface waters. Previous research suggests that weathering solutes are transport limited, and it is hypothesized that revegetation will enhance evapotranspiration (ET) and reduce percolation through the waste rock, potentially reducing loading. This study examined the surface‐atmosphere water and energy exchanges using the eddy covariance technique for three waste rock surfaces with different levels of reclamation: (a) an ~25‐year‐old mixed coniferous forest, (b) a grass site, and (c) bare waste rock. Measurements were taken from May to October in 2013 and 2014. Soil moisture and matric suction were measured to 1‐m depth. Sap flow at the forested site was measured to partition transpiration from total ET. In all years, ET rates were greatest at the forested site, followed by the grass cover and lowest at the bare waste rock site. Growing season ET rates at the forest were 56% higher than grass in 2013 and 35% higher in 2014. At the vegetated sites, climate was the main driver of ET, with high radiation, and warm and dry conditions enhancing fluxes. Maximum ET at these sites corresponded with peak growing season, with vegetation increasing both transpiration and rainfall interception. At the bare rock site, ET was weakly related to atmospheric conditions, and ET rates briefly increased during periods following rainfall when near‐surface soil moisture was enhanced. Transpiration comprised 29% of overall ET at the forest site from late July to early October. Results suggest that vegetation establishment can be incorporated into mine reclamation plans to enhance ET rates and limit percolation, potentially reducing downstream geochemical loads.     

Mineralogical characterization of Baptistina Asteroid Family: Implications for K/T impactor source

Bottke et al. [Bottke, W.F., Vokrouhlicky, D., Nesvorný, D., 2007. Nature 449, 48–53] linked the catastrophic formation of Baptistina Asteroid Family (BAF) to the K/T impact event. This linkage was based on dynamical and compositional evidence, which suggested the impactor had a composition similar to CM2 carbonaceous chondrites. However, our recent study [Reddy, V., Emery, J.P., Gaffey, M.J., Bottke, W.F., Cramer, A., Kelley, M.S., 2009. Meteorit. Planet. Sci. 44, 1917–1927] suggests that the composition of (298) Baptistina is similar to LL-type ordinary chondrites rather than CM2 carbonaceous chondrites. This rules out any possibility of it being related to the source of the K/T impactor, if the impactor was of CM-type composition. Mineralogical study of asteroids in the vicinity of BAF has revealed a plethora of compositional types suggesting a complex formation and evolution environment. A detailed compositional analysis of 16 asteroids suggests several distinct surface assemblages including ordinary chondrites (Gaffey SIV subtype), primitive achondrites (Gaffey SIII subtype), basaltic achondrites (Gaffey SVII subtype and V-type), and a carbonaceous chondrite. Based on our mineralogical analysis we conclude that (298) Baptistina is similar to ordinary chondrites (LL-type) based on olivine and pyroxene mineralogy and moderate albedo. S-type and V-type in and around the vicinity of BAF we characterized show mineralogical affinity to (8) Flora and (4) Vesta and could be part of their families. Smaller BAF asteroids with lower SNR spectra showing only a ‘single’ band are compositionally similar to (298) Baptistina and L/LL chondrites. It is unclear at this point why the silicate absorption bands in spectra of asteroids with formal family definition seem suppressed relative to background population, despite having similar mineralogy.     

A comparison of intertidal species richness and composition between Central California and Oahu,Hawaii

The intertidal zone of tropical islands is particularly poorly known. In contrast, temperate locations such as California's Monterey Bay are fairly well studied. However, even in these locations, studies have tended to focus on a few species or locations. Here we present the results of the first broadscale surveys of invertebrate, fish and algal species richness from a tropical island, Oahu, Hawaii, and a temperate mainland coast, Central California. Data were gathered through surveys of 10 sites in the early 1970s and again in the mid‐1990s in San Mateo and Santa Cruz counties, California, and of nine sites in 2001–2005 on Oahu. Surveys were conducted in a similar manner allowing for a comparison between Oahu and Central California and, for California, a comparison between time periods 24 years apart. We report a previously undocumented richness of intertidal species in both locations: 516 for Oahu and 801 for Central California. Surprisingly, when differences in search efforts are controlled, overall (alpha) diversity appears to be similar between locations, although site level (beta) diversity is much higher in California. Species richness in California generally increased along a wave exposure gradient and distance from an urban area. Much higher numbers of both invasive and endemic species were found on Oahu. In California, more invertebrate species were found in the 1990s, likely due to an improvement in taxonomic resources since the 1970s, and species composition was different in the two surveys due to the high incidence of rare species. Although some southern species increased in number between the two time periods and some northern species decreased, we detected little evidence of change favoring southern or northern species. These results are in line with recent findings that water temperatures in the Monterey Bay have been in a cooling trend since the 1980s, in contrast to many locations elsewhere in the world.     

Modeling River Connectivity Using the Barrier Assessment Tool and Available Data on Registered Dams in the Guadalupe–San Antonio River System,Texas

The rate of dam building has declined in the United States, but dam building is still considered an integral part of water supply management, particularly in arid and semiarid regions. Understanding how dams affect river connectivity is a key component of river basin management. This study analyzed the spatial and temporal patterns of fragmentation in the Guadalupe–San Antonio River System (GSARS) and how these patterns were related to dam size, age, and purpose. Using a shapefile of registered dams and the National Hydrography Dataset High Resolution (NHD-HR) as input data for the Barrier Assessment Tool (BAT), six successive connectivity models were created. The average length of functional river networks (FRNs) decreased over time but the number of FRNs over 100?km stayed relatively stable. Fragmentation in the GSARS was concentrated around urban centers, and the majority of fragmentation occurred gradually as dams separated small FRNs along tributaries and headwaters. This gradual decline in longitudinal connectivity was punctuated by sporadically large separations of river networks by particular dams based on their location and time of commissioning. The methodology presented here provides a way to analyze both the extent and the temporal evolution of fragmentation in a river system. Key Words: Barrier Assessment Tool (BAT), fragmentation, functional river networks, river connectivity.     

Enantioselectivity of polychlorinated biphenyl atropisomers in sediment and biota from the Turtle/Brunswick River estuary, Georgia, USA

To investigate the potential for enantioselective transformation and accumulation, the enantiomer distributions of seven polychlorinated biphenyl (PCB) atropisomers were measured in the sediment and biota from a sub-tropical estuary heavily contaminated with Aroclor 1268, a technical mixture of highly chlorinated PCB congeners. Enantiomer fractions (EFs) of PCBs 91, 95, 136, 149, 174, 176, and 183 in marsh sediment, invertebrate, forage and predatory fish species, and bottlenose dolphins were determined. Non-racemic EFs greater than 0.75 were found in sediments for PCBs 136 and 174, likely the result of microbial dechlorination. Although enantiomer fractions in grass shrimp (Palaemonetes spp.) mirrored those of sediment, fish species had EFs that differed significantly from sediment or grass shrimp. Similarly, bottlenose dolphins were also found to contain non-racemic quantities of PCBs 91, 136, 174, 176, and 183. Non-racemic EFs in these biota were likely a result of both uptake of non-racemic proportions of PCBs from the diet and enantioselective biotransformation.