Narrow Depth Range Research Articles

Design optimisation of permanently installed monitoring system for polycrystalline materials

This article presents a design procedure for structural health monitoring systems based on bulk wave ultrasonic sensors for structures fabricated from polycrystalline materials. When designing a monitoring system, maximum coverage per transducer is a general requirement in order for the system to be economic. For coarse-grained polycrystalline materials, monitoring is often made challenging by low signal-to-noise ratios caused by grain scattering. Therefore, when designing a monitoring system for these materials, in addition to the economic requirement, it needs to be ensured that an adequate signal-to-noise ratio can be obtained throughout the monitoring volume. This typically introduces a trade-off between volume coverage per transducer and sensitivity that must be investigated. In this article, this trade-off is studied and a methodology using signal-to-noise maps is presented to design the system, that is, choose the optimal transducer parameters and placement. First, a combined analytical and numerical approach is used to generate a signal-to-noise map. Then, the influence of various factors on signal-to-noise ratio is investigated. Finally, two representative examples, with different criteria, are given to illustrate the methodology. In one example, the full surface area of the testpiece is covered with transducers and the optimum gives the deepest coverage. The other one aims to achieve the minimum fractional surface area that has to be covered with transducers to monitor a narrow depth range far from the surface, which has a potential application in weld monitoring. Results show that the optimum is likely to be at much lower frequency than typically used in inspection, as tracking signals with time gives sensitivity gains. Experiments were carried out to illustrate that higher volume coverage can be obtained at lower frequencies.

ROV’s Video Recordings as a Tool to Estimate Variation in Megabenthic Epifauna Diversity and Community Composition in the Guaymas Basin

Patterns in benthic megafauna diversity in littoral and intertidal zones in the Gulf of California has been associated as a function of habitat heterogeneity and substrate type. Current knowledge of invertebrate communities in hard bottom habitats at depths >200 m in the Gulf is poor due to the methodological limitations inherent in sampling deep habitats. Using benthic imagery recorded on video coupled with environmental data from the Remotely Operated Vehicle Doc Ricketts, we documented variation in the diversity and community composition of the benthos from 849-990 m depth in the NW limit of the Guaymas Basin in relation to dissolved oxygen and substrate characteristics. This area is affected by the incidence of an oxygen minimum zone where oxygen drops to levels <0.5ml L-1 and strong gradients in a narrow depth range occur. Dissolved oxygen varied along our benthic survey from 0.200 to 0.135 ml L-1. We observed a great taxonomic richness across an area of rocky outcrops through the lower transitional zone. This megafaunal pattern is different to that reported in other oxygen minimum zones where they are characterized by a great abundance of a few species. Taxonomic richness diminished at depths with reduced dissolved oxygen in the lower boundary of the oxygen minimum zone with increasing soft sediment cover. We found that rocky outcrops (including structure-forming organisms such as corals, sponges and oyster aggregations also provide a hard substrate for other fauna) supported a higher diversity (H’= 0.8) than soft sediment (H´=0.7) as have been observed in other habitats such as seamounts. Environmental variables that explained most of the megafaunal variation were substrate type (18.4%), depth (1.14%) and temperature (0.9%). Salinity (0.45%) and dissolved oxygen (0.3%) were less important factors to explain the megafaunal composition variance. Substrate type played a key role in the diversity and composition of benthic megafauna. These results broaden our understanding concerning the potential roles of substrate characteristics in the community composition of the deep-sea benthic megafaunal assemblages in the Gulf of California and oxygen minimum zones in general.

A novel low-cost, high-precision sea temperature sensor for coral reef monitoring

The role of elevated sea temperatures in coral bleaching has been well documented. Many of the sea temperature records utilized for purposes of widespread, multi-species bleaching predictions in recent publications have been acquired through satellite remote sensing. Satellites estimate sea temperatures at only a narrow range of depths near the surface of the ocean and may therefore not adequately represent the true temperatures endured by the world's coral ecosystems. To better characterize sea temperature regimes that coral reef ecosystems experience, as well as better define the individual thresholds for each species that bleaches, in situ sea temperature sensors are required. Commercial sensors are expensive in large quantities, however, reducing the capacity to conduct large- scale research programs to elucidate the range of significant scales of temperature variability. At the National Oceanic and Atmospheric Administration's (NOAA) Atlantic Oceanographic and Meteorological Laboratory (AOML), we designed a low-cost (roughly US$9 in parts) and high- precision sea temperature sensor that uses an Arduino microprocessor board and a high accuracy thermistor. This new temperature sensor autonomously records temperatures onto a memory chip and provides better accuracy (+0.05 °C) than a comparable commercial sensor (+0.2 °C). Moreover, it is not difficult to build; anyone who knows how to solder can build the temperature sensor. In March 2019, students at middle and high schools in Broward County, Florida, built close to 60 temperature sensors. During 2019, these sensors will be deployed by Reef Check, a global-scale coral reef monitoring organization, as well as by other programs to determine worldwide sea temperature regimes through the Opuhala Project (https://www. coral. noaa. gov/opuhala). This paper chronicles results from the initial proof-of-concept deployments for these AOML-designed sensors.

Evaluation of a geotechnical compaction model to estimate sediment deformation

AbstractA geoarchaeological and pedoarchaeological approach to compaction disturbance is necessary for successful archaeological interpretation of potentially compacted deposits. When surface ruts from vehicle activity occur above archaeological deposits, there is a potential for impact to the archaeological record to occur. While impacts to the soil surface are relatively straightforward to describe, sub‐surface disturbances are more difficult to quantify. Compaction disturbances to buried archaeological deposits can impact the superposition of artefacts, buried soil horizons, and stratigraphy across space, and make interpretation difficult or impossible. Deposits can be damaged by both movement through surface disturbances, and by translocation from compaction events. It is important to consider and take both impact types into account. Here, we present a geotechnical compaction model that can be used to assist with sub‐surface characterization under vehicle ruts formed during off‐road travel. The model is based on a Boussinesq analysis of stress increase below a surface load. The change in bulk density resulting from compaction is assumed to be proportional to the stress increase. The model results were compared against pilot‐scale tests conducted with homogeneous sediment and field‐scale in situ tests. The results indicate that the model generally agreed with measurements to within 20%, although only a single soil type was evaluated in these studies, with a narrow range of initial bulk densities and rut depths. While application of the model across a broader matrix of soil types, bulk densities and rut depths would increase confidence in the model, it appears that the model may be suitable for use in archaeological field investigations. Potential uses include both compliance and research‐based field applications.

Movements of a potential fishery resource, porcupine crab (Neolithodes grimaldii) in Northern Davis Strait, Eastern Canadian Arctic

Climate change is positioning deep-sea lithodid crab species to expand their distributions. In Canada's Eastern Arctic, there is additional interest in the lithodid crab, Neolithodes grimaldii, (or porcupine crab) as a potential fisheries resource, as high biomass has been observed through incidental bycatch in the Greenland halibut (Reinhardtius hippoglossoides) fishery. This study aimed to advance our knowledge of the biology of the porcupine crab by addressing undescribed aspects of the crabs' spatiotemporal distribution. We administered pop-up archival tags (mrPATs and miniPATs) on 18 porcupine crabs and tracked their movements in Davis Strait at ~900 m depth. The tags were programmed to release sequentially, providing the location of a crab every six days across the study period (July–October 2018). Of the 18 tags, 17 (94%) successfully reported locations and six of those (35%) popped-off on the programmed date. A systematic method was established to estimate the most accurate final location of each crab, considering error introduced by tag drift (horizontal and vertical) and by satellite location accuracy. Six crabs (35%) moved between 3.1 and 33 km away from the deployment site over the course of 19 - 66 days, while the rest remained highly site attached moving <1 km. Crabs moved in a southern direction away from the deployment site; however, the broad range of this directional movement (113.6° – 283.7°), provides little support for coordinated group movement. Crabs also remained within a narrow depth and thermal range for the study period. To our knowledge, this study is the first to administer pop-up archival tags on porcupine crabs revealing a new technique to investigate their spatiotemporal movements. We propose further telemetry work to support the development of an offshore porcupine crab fishery in the Canadian Arctic.

Quantifying wetland plant vertical root distribution for estimating the Interface with the anoxic zone

Plant roots control many important interactions in the wetland anoxic zone such as carbon deposition, gas exchange, and nutrient dynamics, yet few studies document the vertical depth distribution of fine roots which mediates these interactions. Excavated root systems of a wetland sedge and shrub were scanned. Utilizing Root System Analyzer, normalized root length per 5 cm depth interval were quantified for 10 samples of each species. Utilizing bootstrapping, root length per depth interval for each root class was fitted to a density distribution function and matched to water table depth. Vertical root length distributions varied by root class, with shrub fine roots constrained to a narrow depth range. Between 1999 and 2010, the interface with the anoxic zone can vary by a factor of four between wet and dry years. Compared to estimates of root vertical distribution based on biomass, this study indicates a considerably higher portion of the fine roots occur in anoxic soil. Accurately quantifying the spatial distribution of the fine roots, root tips, and other sites associated with exudation is crucial for determining the strength of root-methanogen interactions.

4He irradiation of zircon, ZrSiO4, using a micro-patterned, Si-based energy filter

The quantitative evaluation of alpha-particle damage in the mineral zircon, ZrSiO4, using 4He irradiation experiments is difficult because the vast majority of atomic knock-ons in the target are concentrated in a narrow depth range near the ends of the He-ion trajectories. Here we present a new concept to overcome this problem, namely, tailoring the depth profile of damage by means of a micromechanically fabricated “energy filter”. Lamellae of 1.5 μm thickness, prepared from ZrSiO4 using the focused-ion-beam technique, were subjected to irradiation with 8.8 MeV 4He ions. Five irradiations with ion fluences in the range 2.5 × 1015–1 × 1017 cm−2 have resulted in mild to severe damage, as monitored by the broadening and downshift of SiO4-stretching Raman bands. Our results may provide a means for quantifying the contribution of alpha particles to the total self-irradiation damage in zircon.

Longer mesocotyl contributes to quick seedling establishment, improved root anchorage, and early vigor of deep-sown rice

Dry direct seeding of rice (DDSR) is practiced as a technique to address drought in tropical Asia, as it requires less water than transplanting. However, rice has a narrow range of optimal sowing depth, and deep sowing often causes poor seedling emergence. The objective of this study was to elucidate differences among rice cultivars in their tolerance to deep sowing (i.e., the ability to show vigorous seedling emergence from deep soil) and the traits associated with this vigor. Two-year on-farm research in rainfed lowlands showed mean seeding depths of 16.1–35.0 mm (a coefficient of variation of 27%–49%). The deep-sowing tolerance differed significantly among 16 cultivars in research station field experiments. The emergence of seedlings from sowing at a depth of 85 mm was >80% in tolerant cultivars versus <1% in cultivars popular with farmers. Deep-sowing tolerance was attributable primarily to the elongation ability of the mesocotyl and, to a lesser extent, of the 1st internode. In a pot experiment that simulated drought around the time of sowing, seedlings that germinated from deeper soil had greater emergence and greater shoot and root growth than those that emerged from shallow soil, as the deeper seeds could acquire residual soil moisture. Our results suggest that improving the tolerance of rice to deep sowing should stabilize seedling establishment in DDSR. Cultivars that tolerate deep sowing will allow further development of the deep sowing technique and reduce the risk of sowing failure caused by drought during seedling emergence in water-scarce environments.

Field evidence for the lateral emplacement of igneous dykes

Seismological and geodetic data from modern volcanic systems strongly suggest that magma is transported significant distance (tens of kilometres) in the subsurface away from central volcanic vents. Geological evidence for lateral emplacement preserved within exposed dykes includes aligned fabrics of vesicles and phenocrysts, striations on wall rocks and the anisotropy of magnetic susceptibility. In this paper, we present geometrical evidence for the lateral emplacement of segmented dykes restricted to a narrow depth range in the crust. Near-total exposure of three dykes on wave cut platforms around Birsay (Orkney, UK) are used to map out floor and roof contacts of neighbouring dyke segments in relay zones. The field evidence suggests emplacement from the WSW towards the ENE, and that the dykes are segmented over their entire vertical extent. Geometrical evidence for the lateral emplacement of segmented dykes is likely more robust than inferences drawn from flow-related fabrics, due to the prevalence of ubiquitous ‘drainback’ events (i.e. magmatic flow reversals) observed in modern systems.

Quantifying shorebird habitat in managed wetlands by modeling shallow water depth dynamics.

Over 50% of Western Hemisphere shorebird species are in decline due to ongoing habitat loss and degradation. In some regions of high wetland loss, shorebirds are heavily reliant on a core network of remaining human-managed wetlands during migration journeys in the spring and fall. While most refuges have been designed and managed to match the habitat needs of waterfowl, shorebirds typically require much shallower water (<10cm deep). Traditional static habitat modeling approaches at relatively coarse spatial and temporal resolution are insufficient to capture dynamic changes within this narrow water depth range. Our objectives were to (1) develop a method to quantify shallow water habitat distributions in inland non-tidal wetlands, and (2) to assess how water management practices affect the amount of shorebird habitat in Sacramento National Wildlife Refuge Complex. We produced water depth distributions and modeled optimal habitat (<10cm deep) within 23 managed wetlands using high-resolution topography and fixed-point water depth records. We also demonstrated that habitat availability, specifically suitable water depth ranges, can be tracked from satellite imagery and high-resolution topography. We found that wetlands with lower topographic roughness may have a higher potential to provide shorebird habitat and that strategically reducing water levels could increase habitat extent. Over 50% of the wetlands measured provided optimal habitat across <10% of their area at the peak of migration in early April, and most provided a brief duration of shallow water habitat. Reducing water volumes could increase the proportion of optimal habitat by 1-1,678% (mean=294%) compared to actual volumes measured at peak spring migration in 2016. For wetlands with a high habitat potential, beginning wetland drawdown earlier and extending drawdown time could dramatically improve habitat conditions at the peak of shorebird migration. Our approach can be adapted to track dynamic hydrologic changes at broader spatial scales as additional high-resolution topographic (e.g., lidar, drone imagery photogrammetry) and optical remote sensing data (e.g., planet imagery, drone photography) become available.

ON «STEP OF ALLOCATION» AND FORECASTING OF THE VEIN GOLD ORE BODIES

On the example of a number of domestic and foreign gold vein deposits it has been shown that the system of gold-ore bodies is located along some narrow local ore controlling displacements in a shape of veins. These veins are located at approximately equal distances from each other - at allocation step. This step varies from 30—70 m to 100— 250 m for different deposits. It allows forecasting of ore bodies at the flanks of the displacements and exploration by drilling. On the example of near-surface deposits it has been confirmed that such ore bodies can be formed at two vertical ore-bearing levels — upper and lower (deep). The upper level appears at very narrow vertical range of depths (100-300 m) near the paleosurface, presumably in the alumstone-adular-kaolinic metasomatites. Here the rhythmically-banded ores with low-grade gold are formed. At the lower (deep) level, the ore bodies can be formed in the interval of 600-1000 m and deeper from the paleosurface in the zones of tectonic breccia, crossing the metasomatites of the secondary quartzites type. They are more often to be the place of the localization of breccia structure ores with comparatively high-grade gold. So, at the near-surface deposits it is possible to explore the new (in particular, blind) ore bodies in allocation step distance from each other at two levels of mineralization, and, moreover, at the significant depth.

Deepest and hottest hydrothermal activity in the Okinawa Trough: the Yokosuka site at Yaeyama Knoll.

Since the initial discovery of hydrothermal vents in 1977, these ‘extreme’ chemosynthetic systems have been a focus of interdisciplinary research. The Okinawa Trough (OT), located in the semi-enclosed East China Sea between the Eurasian continent and the Ryukyu arc, hosts more than 20 known vent sites but all within a relatively narrow depth range (600–1880 m). Depth is a significant factor in determining fluid temperature and chemistry, as well as biological composition. However, due to the narrow depth range of known sites, the actual influence of depth here has been poorly resolved. Here, the Yokosuka site (2190 m), the first OT vent exceeding 2000 m depth is reported. A highly active hydrothermal vent site centred around four active vent chimneys reaching 364°C in temperature, it is the hottest in the OT. Notable Cl depletion (130 mM) and both high H2 and CH4 concentrations (approx. 10 mM) probably result from subcritical phase separation and thermal decomposition of sedimentary organic matter. Microbiota and fauna were generally similar to other sites in the OT, although with some different characteristics. In terms of microbiota, the H2-rich vent fluids in Neuschwanstein chimney resulted in the dominance of hydrogenotrophic chemolithoautotrophs such as Thioreductor and Desulfobacterium. For fauna, the dominance of the deep-sea mussel Bathymodiolus aduloides is surprising given other nearby vent sites are usually dominated by B. platifrons and/or B. japonicus, and a sponge field in the periphery dominated by Poecilosclerida is unusual for OT vents. Our insights from the Yokosuka site implies that although the distribution of animal species may be linked to depth, the constraint is perhaps not water pressure and resulting chemical properties of the vent fluid but instead physical properties of the surrounding seawater. The potential significance of these preliminary results and prospect for future research on this unique site are discussed.

Seismic scatterers in the mid-lower mantle beneath Tonga-Fiji

We analyze deep and intermediate-depth earthquakes at the Tonga-Fiji region in order to reveal the distribution of scattering objects in the mid-lower mantle. By array processing waveform data recorded at regional seismograph stations in the US, Alaska, and Japan, we investigate S-to-P scattering waves in the P coda, which arise from kilometer-scale chemically distinct objects in the mid-lower mantle beneath Tonga-Fiji.With ten scatterers previously reported by the author included, twenty-three mid-lower mantle scatterers have been detected below 900 km depth, while scatterers deeper than 1900 km have not been identified. Strong mid-lower mantle S-to-P scattering most frequently occurs at the scatterers located within a depth range between 1400 km and 1600 km. The number of scatterers decreases below 1600 km depth, and the deeper objects tend to be weaker. The scatterer distribution may reflect diminishing elastic anomalies of basaltic rocks with depth relative to the surrounding mantle rocks, which mineral physics has predicted to occur. The predominant occurrence of strong S-to-P scattering waves within a narrow depth range may reflect significant reduction of rigidity due to the ferro-elastic transformation of stishovite in basaltic rocks.Very large signals associated with mid-mantle scatterers are observed only for a small portion of the entire earthquake-array pairs. Such infrequent observations of large scattering signals, combined with quite large event-to-event differences in the scattering intensity for each scatterer, suggest both that the strong arrivals approximately represent ray theoretical S-to-P converted waves at objects with a plane geometry. The plane portions of the strong scatterers may often dip steeply, with the size exceeding 100 km. For a few strong scatterers, the range of receivers showing clear scattered waves varies substantially from earthquake-array pair to pair. Some of the scatterers are also observed at different arrays that have significantly different directions of incident waves to the scatterers. Furthermore, weak but coherent P-to-P scattered waves as well as S-to-P waves are observed for a few of the scatterers. These observations indicate that the locally plane scatterers also possess substantial topography.

Microhabitat estimation of an imperiled headwater fish, the Yazoo darter (Etheostoma raneyi), in coastal plain streams

Headwater fishes in the southeastern United States make up much of the fish biodiversity of the region yet many are imperiled. Despite this, the specific habitat requirements of imperiled headwater fishes in lowland Coastal Plain streams have rarely been quantified. Using data collected over three years of seasonal sampling we provide estimates of the microhabitat requirements of the imperiled Yazoo darter (Etheostoma raneyi Suttkus and Bart), a small benthic insectivore. Our results indicate that the species is a microhabitat specialist and that optimum microhabitat within degraded contemporary streams consists of a narrow range of water depths (about 20–30 cm), current velocity ≥ 0.25 m·s−1, complex stable debris piles, rooted macrophytes, and likely coarse substrate. No pronounced or generalized seasonal shifts in microhabitat use occurs, and no evidence exists for intraspecific partitioning of microhabitat. Though stable and complex instream cover is one of the most important variables explaining variation in microhabitat use by Yazoo darters, such cover is rare in the degraded streams within the range of the species. Current conservation classifications of the Yazoo darter by governmental agencies and nongovernmental organizations as well as associated management plans that are based on the assumption that Yazoo darters are habitat generalists should be reviewed in recognition of the increased risk of decline because Yazoo darters are microhabitat specialists. These considerations should also be extended to other closely related imperiled species of snubnose darters.

Idealized Tropical Cyclone Responses to the Height and Depth of Environmental Vertical Wind Shear

Abstract Three sets of idealized, cloud-resolving simulations are performed to investigate the sensitivity of tropical cyclone (TC) structure and intensity to the height and depth of environmental vertical wind shear. In the first two sets of simulations, shear height and depth are varied independently; in the third set, orthogonal polynomial expansions are used to facilitate a joint sensitivity analysis. Despite all simulations having the same westerly deep-layer (200–850 hPa) shear of 10 m s−1, different intensity and structural evolutions are observed, suggesting the deep-layer shear alone may not be sufficient for understanding or predicting the impact of vertical wind shear on TCs. In general, vertical wind shear that is shallower and lower in the troposphere is more destructive to model TCs because it tilts the TC vortex farther into the downshear-left quadrant. The vortices that tilt the most are unable to precess upshear and realign, resulting in their failure to intensify. Shear height appears to modulate this tilt response by modifying the thermodynamic environment above the developing vortex early in the simulations, while shear depth modulates the tilt response by controlling the vertical extent of the convective vortex. It is also found that TC intensity predictability is reduced in a narrow range of shear heights and depths. This result underscores the importance of accurately observing the large-scale environmental flow for improving TC intensity forecasts, and for anticipating when such forecasts are likely to have large errors.

Arctic charr exploit restricted urbanized coastal areas during marine migration: Could they be in harm’s way?

Human and industrial activities in Arctic areas are increasing, as are global water temperatures. Combined, these factors can result in altered conditions for species living in these, until recently, pristine areas. Of the anadromous salmonids, Arctic charr may be particularly vulnerable to these changes, as this species is adapted to cold waters and exploits restricted areas at sea. In order to test to what extent Arctic charr utilized coastal areas with anthropogenic interference versus more pristine waters, the marine area use of a population in northern Norway was documented over three consecutive years by use of acoustic telemetry. Their depth utilization, temperature preference and survival was also recorded. The tagged fish spent a minimum of half of their marine residency time within 5 km of the river outlet proximate to urbanized coastal areas. The fish also resided within a narrow temperature and depth range and spent a very limited period at sea. The marine habitat available to Arctic charr should be carefully considered in coastal development and management plans, as human activities and coastal water temperatures increase in the Arctic regions. The current study illustrates the importance of species and population-specific knowledge during development of management strategies for anadromous salmonids.

A high-resolution record of Southern Ocean intermediate water radiocarbon over the past 30,000 years

The circulation of intermediate waters plays an important role in global heat and carbon transport in the ocean and changes in their distribution are closely tied to glacial–interglacial climate change. Coupled radiocarbon and U/Th measurements on deep-sea Desmophyllum dianthus corals allow for the reconstruction of past intermediate water ventilation. We present a high-resolution time series of Antarctic Intermediate Water radiocarbon from 44 corals spanning 30 ka through the start of the Holocene, encompassing the transition into the Last Glacial Maximum (LGM) and the last deglaciation. Corals were collected south of Tasmania from water depths between 1430 and 1950 m with 80% of them between 1500 and 1700 m, giving us a continuous record from a narrow depth range. The record shows three distinct periods of circulation: the MIS 3–2 transition, the LGM/Heinrich Stadial 1 (extending from ∼22 to 16 kyr BP), and the Antarctic Cold Reversal (ACR). The MIS 3–2 transition and the ACR are characterized by abrupt changes in intermediate water radiocarbon while the LGM time period generally follows the atmosphere at a constant offset, in support of the idea that the LGM ocean was at steady state for its 14C distribution. Closer inspection of the LGM time period reveals a 40‰ jump at ∼19 ka from an atmospheric offset of roughly 230‰ to 190‰, coincident with an observed 10–15 m rise in sea level and a southward shift of the Subantarctic and Polar Fronts, an abrupt change not seen in deeper records. During the ACR time period intermediate water radiocarbon is on average less offset from the atmosphere (∼110‰) and much more variable. This variability has been captured within the lifetimes of three individual corals with changes of up to 35‰ over ∼40 yr, likely caused by the movement of Southern Ocean fronts. This surprising result of relatively young and variable intermediate water radiocarbon during the ACR seems to go against the canonical idea of reduced circulation and ventilation in the south during this time period. However comparisons with other records from the Southern Ocean highlight zonal asymmetries, which can explain the deviation of our Tasmanian record from those in Drake Passage and the eastern Pacific. These signals seen in Tasmanian intermediate water Δ14C can also be found in Greenland ice core δ18O and East Asian monsoon strength. Throughout the LGM and the deglaciation, our Tasmanian intermediate water record is sensitive to times when the upper and lower cells of the meridional overturning circulation are more or less interconnected, which has important implications for the global climate system on glacial–interglacial time scales.

How effective are ecological traits against drilling predation? Insights from recent bivalve assemblages of the northern Red Sea

Biotic interactions, especially predation, have drawn considerable attention in recent times as an important agent of natural selection. Drilling predation is often used as a model system by paleobiologists to evaluate evolutionary and ecological effects of such predatory interaction on the composition of molluscan communities. Using drilling frequencies, it is possible to test quantitatively specific predictions that postulate the effectiveness of ecological traits against predation in present-day environments. The high frequency of drilling (DF) in a diverse recent bivalve assemblage from shallow water environments of the northern Red Sea enables us to test such evolutionary hypotheses, predicting low DF in large-sized bivalves, in infaunal bivalves, in siphonate and mobile bivalves, lower DF in bysally attached than in other epifaunal bivalves, and high DF in bivalves occurring in shallow habitats. We evaluate these predictions on the basis of more than 15,000 bivalve specimens collected at stations with meter-scale spatial resolution using three different methods to calculate DF, namely 1) per-species per-station DF, 2) per-species DF by pooling all stations, and 3) per-station DF by pooling all species. The results are not always consistent among these three methods. Among morphological attributes, we found size and shape of a species to be a good predictor of drilling frequency. However, life habit shows a pattern contrary to our prediction because infaunal groups show the highest DF. Although we did not find any significant correlation between predator abundance and DF at small spatial (station) scales, the dominance of naticid gastropods and low abundance of muricid gastropods at regional scales can explain the much higher DF observed in infauna than in epifauna. Characteristics of the siphon or mobility did not always play a major role in dictating the DF. Attachment type of epifauna does not always show a predictable pattern in deterring drilling predation; however, bysally attached bivalves sometimes show a slightly lower DF compared to cemented bivalves. Although water depth has no significant effect on DF, it might be influenced by the relatively narrow depth range of the stations. We did not find significant variation in DF between groups adapted to different habitats (i.e, substrate types); however, DF seems to differ between groups with different feeding mode. Our study demonstrates that some ecological traits (such as infaunalization or predator avoidance by choosing deeper habitat) that are claimed to be anti-predatory, do not offer effective defense against drilling predation in present-day environments—a result consistent with the idea of ever escalating predator-prey dynamics.

Optimized real-time monitoring of glutathione redox status in single pyramidal neurons in organotypic hippocampal slices during oxygen-glucose deprivation and reperfusion.

A redox-sensitive Grx1-roGFP2 fusion protein was introduced by transfection into single pyramidal neurons in the CA1 subfield of organotypic hippocampal slice cultures (OHSCs). We assessed changes in the GSH system in neuronal cytoplasm and mitochondria during oxygen-glucose deprivation and reperfusion (OGD/RP), an in vitro model of stroke. Pyramidal cells in a narrow range of depths below the surface of the OHSC were transfected by gene gun or single-cell electroporation with cyto- or mito-Grx1-roGFP2. To mimic the conditions of acute stroke, we developed an optimized superfusion system with the capability of rapid and reproducible exchange of the solution bathing the OHSCs. Measurements of pO2 as a function of tissue depth show that in the region containing the transfected cells, the pO2 is well-controlled. We also found that the pO2 changes on the same time scale as changes in intracranial pressure, cerebral blood flow, and pO2 during acute stroke. Determining the reduction potential, EGSH, from the ratiometric fluorescence signal requires an absolute intensity measurement during calibration of the Grx1-roGFP2. Using the signal from cotransfected tdTomato as an internal standard during calibration improves quantitative measurements of Grx1-roGFP2 redox status and allows EGSH to be determined. EGSH becomes more reducing during OGD and more oxidizing during RP in mitochondria while changes in cytoplasm are not significant compared with controls.

Female stickleback prefer shallow males: Sexual selection on nest microhabitat

Sexual selection is most often thought of as acting on organismal traits, such as size or color. However, individuals' habitat use may also affect mating success. Here, we show that, in threespine stickleback, nest depth can be a target of sexual selection. In postglacial lakes in British Columbia, male threespine stickleback nest in a narrow range of depths. Prior studies revealed heritable variation in males' preferred nest microhabitat. We surveyed four natural populations, finding that male stickleback with shallower nests were more successful at breeding. Indeed, nest depth was a much stronger predictor of male mating success than more commonly studied targets of sexual selection in stickleback (size, condition, shape, color, infection status). This selection on nest depth means that variance in fitness changed predictably across microhabitats, altering the opportunity for sexual selection to act on other traits. Accordingly, we show that sexual selection on other male traits is strongest where variance in nesting success is highest (at intermediate nest depths in some lakes). We conclude that males' choice of nesting microhabitat is an especially important target of sexual selection, resulting in fine-scale spatial variation in sexual selection on other traits.