Surface Aggregations Research Articles

Nano-topographical surface engineering for enhancing bioactivity of PEEK implants (in vitro—histomorphometric study)

ObjectivesDental implants are currently becoming a routine treatment decision in dentistry. Synthetic polyetheretherketone (PEEK) polymer is a prevalent component of dental implantology field. The current study aimed to assess the influence of Nd:YAG laser nano-topographical surface engineering combined with ultraviolet light or platelet rich fibrin on the bioactivity and osseointegration of PEEK implants in laboratory and animal testing model.Materials and methodsComputer Aided Design-Computer Aided Manufacturing (CAD CAM) discs of PEEK were used to fabricate PEEK discs (8 mm × 3 mm) N = 36 and implant cylinders (3 mm × 6 mm) N = 72. Specimens were exposed to Nd:YAG laser at wavelength 1064 nm, and surface roughness topography/Ra parameter was recorded in nanometer using atomic force microscopy. Laser modified specimens were divided into three groups: Nd:YAG laser engineered surfaces (control), Nd:YAG laser/UV engineered surfaces and Nd:YAG laser/PRF engineered surfaces (N = 12 discs–N = 24 implants). In vitro bioactivity test was performed, and precipitated apatite minerals were assessed with X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM). In vivo histomorphometric analysis was performed in rabbits with BIC% calculation.ResultsRa mean value of PEEK laser engineered surfaces was 125.179 nm. For the studied groups, XRD patterns revealed distinctive peaks of different apatite minerals that were demonstrated by SEM as dispersed surface aggregations. There was a significant increase in the BIC% from control group 56.43 (0.97) to laser/UV surfaces 77.30 (0.78) to laser/PRF 84.80 (1.29) (< 0.0001).ConclusionsSuccessful engineered nano-topographical biomimetic PEEK implant could be achieved by Nd:YAG laser technique associated with improving bioactivity. The combination with UV or PRF could be simple and economic methods to gain more significant improvement of PEEK implant surface bioactivity with superior osteointegration.

Trichodesmium Around Australia: A View From Space

AbstractThe cyanobacterium Trichodesmium is responsible for approximately half of the ocean's nitrogen input through nitrogen fixation. Although it was first recorded near Australia in the 18th century, the knowledge of where and when large quantity of Trichodesmium around Australia could be found is still lacking. Here, using multi‐band satellite imagery acquired between 2012 and 2021, we fill this knowledge gap through the use of deep learning, designed to recognize both the spectral shapes of individual pixels and spatial morphology of surface aggregations (scums) of Trichodesmium. Trichodesmium scums were found nearly everywhere around Australia, with a cumulative footprint (i.e., where the 10‐year average density is &gt;0.001‰) exceeding 4.6 million km2. Strong seasonality was found, with peak months between September and November. Furthermore, temperature, iron‐rich dust and black carbon aerosols, with the latter being a result of frequent bushfires, play major roles in determining the spatial distributions and seasonality of Trichodesmium.

Assessing individual movement, habitat use, and behavior of non-breeding marine birds in relation to prey availability in the US Atlantic

Resource availability is a key factor driving marine bird movements and distributions, but direct information on prey availability is difficult to obtain at relevant scales. We present novel methods for describing multi-scale trophic associations, combining movement analyses of marine birds with estimates of forage fish surface aggregations from digital aerial survey data and species occupancy from bottom trawl survey data. We analyzed satellite telemetry data from northern gannets Morus bassanus, red-throated loons Gavia stellata, and long-tailed ducks Clangula hyemalis in the US Atlantic during the non-breeding period. Using discrete-time hidden Markov models to distinguish area-restricted (i.e. putative foraging) from transit movements, we examined how environmental factors influence movement, and how forage fish species distributions and surface aggregations influence habitat use by gannets and loons that have greater dietary reliance. Our results suggest that chlorophyll a concentration significantly affected movement behavior across species, highlighting the importance of higher-productivity areas around estuaries during colder months when regional productivity is low. Though variable across species and seasons, spatial cross-correlation analysis revealed that herring species (Family Clupeidae), including Atlantic menhaden Brevoortia tyrannus, may be important resources; it also showed positive spatial correlations with forage fish aggregations. This suggests that prey patch dynamics and factors driving aggregation formation may be as important as species composition. However, spatial patterns were generally low (&lt;0.3), suggesting a mismatch in spatiotemporal resolution, exemplifying the challenges in quantifying trophic relationships in marine systems. Disentangling predator-prey relationships is critical to understanding the mechanisms driving marine bird behavior in rapidly changing marine systems.

Unraveling the importance between electronic intensity and oxygen vacancy on photothermocatalytic toluene oxidation over CeO2

• CeO 2 with different electron density is obtained via regulation on facet and oxygen vacancy. • High electron density plays more important role than oxygen vacancy in photothermocatalytic toluene oxidation. • Toluene conversion rate can achieve 93% at 145 °C under GHSV of 60,000 mL·g −1 ·h −1 . • Decrement of electron density and increase of oxygen vacancy are responsible for the decline of activity. Developing low-temperature, high-efficiency and anti-poisoning catalysts is crucial for VOCs removal. CeO 2 materials with different electron density are prepared via regulation on facets and oxygen vacancies. It reveals that high electron density of materials plays a decisive role in the production of reactive oxygen species, reducibility of surface lattice oxygen and improvement of photothermocatalytic activity for toluene oxidation compared with highly concentrated oxygen vacancies and large special surface area. Photothermocatalytic conversion rate for 1500 ppm of toluene over the optimized defective CeO 2 could reach 93 % at 145 °C under the gas hourly space velocity of 60,000 mL·g −1 ·h −1 . H 2 -TPR result shows that excessive oxygen vacancies are detrimental to the appearance of mobile reactive oxygen species due to the strong chemical interaction and the escape probability of surface lattice oxygen of CeO 2 . It is also found that the decrement of electron density of the recovered sample can account for the slight catalyst deactivation, accompanied by the increasement of bulk oxygen vacancies in the recovered sample, exclusive of disappearance of surface oxygen vacancies, aggregations and deposition of organic carbon. This work provides an insight into the design of high-efficiency non-noble catalysts applied to VOCs removal.

Surface aggregations ofCalanus finmarchicusduring the polar night

AbstractWhile marine ecosystems in polar areas were thought to be mostly inactive during the polar night, recent observations in the Arctic highlight that dynamic biological interactions occur across all trophic levels. One particularly interesting observation made repeatedly is the occurrence of Calanus finmarchicus, a key species at the base of the food web, in the upper part of the water column in early January. This contrasts with the confirmed life cycle of this copepod, which predicts descent to overwintering depths in autumn and ascent at the end of the winter. Here, we compiled 6 years of data from the polar night to explore this unusual behaviour and to investigate the underlying mechanisms that may cause these surface aggregations. Highest abundance of C. finmarchicus in surface waters was closely related to Polar Surface Water in the vicinity of the sea ice edge. A total of six hypotheses are assessed to explain this distribution pattern, which includes passive transport and active behaviour as a way to improve survival chances or food access. In the context of climate change and sea ice decrease, the presence of lipid-rich copepods in cold surface waters could be a key parameter in driving the spatial distributions of top predators in the Arctic.

Remote sensing of brine shrimp cysts in salt lakes

Using laboratory and field experiments as well as spectral analysis of satellite images, we demonstrate that surface aggregations of brine shrimp (Artemia) cysts (BSC) in salt lakes can be identified unambiguously in satellite imagery. This is because of the unique reflectance spectral shapes of the BSC image slicks, where a sharp and monotonic increase in reflectance is found at wavelengths >550 nm and two inflection points are found around ~550 nm and ~ 650 nm. Such spectral characteristics differentiate BSC slicks from other floating matters. Based on this principle, a deep learning model is developed to extract BSC features from MERIS (Medium Resolution Imaging Spectrometer, 2002–2012) and OLCI (Ocean and Land Color Instrument, 2016 - present) satellite images to quantify BSC abundance, spatial distribution patterns, and their temporal changes in the Great Salt Lake (GSL), the world's largest contributor of BSC commercial products. A clear seasonality is found in BSC abundance, with the primary peak in April – May and secondary peak in October – November. The two peaks may be explained by food availability to brine shrimp. The inter-annual variability and the recent increasing trend in BSC abundance, on the other hand, are difficult to explain by fluctuations in wind, temperature, or salinity, while recent increase in commercial harvest does not appear to be associated with the variability in BSC abundance estimated by satellites. Because many salt lakes around the world, for example the Aral Sea, Lake Urmia, and the Dead Sea, also show BSC slicks in satellite imagery, this study suggests that it is possible to perform a systematic evaluation of BSC abundance and possibly brine shrimp populations in all major salt lakes, especially under a changing climate and increased human activities.

Biocrust islands enhance infiltration, and reduce runoff and sediment yield on a heavily salinized dryland soil

Salinity and sodicity are major forms of land degradation in drylands worldwide, reducing soil function, and threatening pastoral livelihoods. Dryland soils are often dominated by biocrusts, surface aggregations of lichens, bryophytes, fungi and other minute organisms that stabilize surface soils. Biocrusts could have a role in maintaining hydrological functions in heavily salinized areas, but there have been few studies, and the mechanisms are poorly understood. We tested whether biocrust mosses and lichens enhanced infiltration, and reduced runoff and sediment yield, on biocrusted islands scattered among extensive patches of bare highly saline soils in northeaster Iran. Biocrusted soils had greater cumulative infiltration and hydraulic conductivity, less runoff, which commenced later, and lower sediment yields than bare soils. The water content of biocrusted soils was greater than bare soils, but only at low matric potentials. Biocrusted surfaces were alkaline, more sandy, had lower levels of sodium, chloride, and calcium-plus-magnesium ions, and a lower sodium absorption ratio than bare soils. Structural equation modelling showed that increasing salinity was associated with a suppression of the negative effect of biocrusts on runoff. Potential mechanisms for reduced runoff likely relate to enhanced soil aggregation and porosity of biocrusted soils leading to greater retention of soil water content at low matric potentials, as well as an ability of mosses and lichens to capture and store surface water or to permit infiltration into the uppermost surface layers. Overall, our findings reveal a strong association between moss- and lichen-dominant biocrusts and soil hydrological processes, and suggest that these crusts play an important role in maintaining hydrological function in heavily salinized soils.

Salmon lice nauplii and copepodids display different vertical migration patterns in response to light

Light is a fundamental environmental cue which influences the migration of many marine organisms. For the salmon louse Lepeophtheirus salmonis, light is believed to drive the diel vertical migration behaviour of their planktonic larvae. Salmon lice are of critical importance to the salmonid industry due to the damage they cause to wild and farmed hosts. Salmon lice larvae have an eyespot and are positively phototactic, yet how light intensity alters their vertical distribution remains unclear. Here, we tested how light intensity (0, 0.5, 10 and 80 µmol m-2 s-1), dispersal duration (1, 4 and 12 h) and release point (surface or bottom) influenced the vertical migration of salmon lice nauplii and copepodids under controlled conditions in experimental columns. Overall, higher light intensity increased the proportion of nauplii that aggregated at the surface. Copepodid behaviour differed from that of nauplii, as they swam upwards in both light and fully dark conditions, and surface aggregations increased with dispersal duration. Results from the experiments did not support the existing view that light strongly influences the vertical position of copepodids in the water column. Combined with previous work, our results reveal that salmon lice larval stages display different vertical responses to light, temperature and salinity, which may be explained by the different strategies of nauplii (maximise survival and dispersal) and copepodids (maximise host-finding success). Our results have implications for salmon lice dispersal models, where responses of copepodids and nauplii to light are currently parametrised by the same equations. Implementing stage-specific behaviours towards light may improve the outputs of dispersal models.

A report of unusual aggregation behaviour in Bullsnakes (&lt;i&gt;Pituophis catenifer sayi&lt;/i&gt;) near a nest site in Saskatchewan

We describe an unusual aggregation of Bullsnakes (Pituophis catenifer sayi) near a nest site in Saskatchewan. Bullsnake is a wide-ranging oviparous colubrid that reaches the northern tip of its continental range on the prairies and badlands of Canada. At that location, it is considered a species of Special Concern, but, until recently, has been the subject of relatively few natural history reports. This is significant, because, at the northern edge of their range, Bullsnakes may behave differently than elsewhere due to thermal limitations experienced at high latitudes. On 29 June 2019, we observed a mass of five adult Bullsnakes in a Silver Sagebrush (Artemisia cana) shrub on a slope in southwestern Saskatchewan. Aggregations of Bullsnakes are known to occur at hibernacula, during mating, and inside nest chambers before and after oviposition. However, we are unaware of the occurrence of surface aggregations in any other situation. We suggest that these Bullsnakes may have been exhibiting communal gestation, a behaviour thought to be rare in oviparous snakes whereby gravid females congregate before parturition or oviposition for thermal stability or protection from predators.

Probiotic Characteristics and Antifungal Activity of Lactobacillus plantarum and Its Impact on Fermentation of Italian Ryegrass at Low Moisture

The study aimed to investigate probiotic characteristics, and low moisture silage fermentation capability of selected lactic acid bacteria (LAB) isolated from Alfalfa (Medicago sativa L). Morphological and physiological properties, carbohydrates fermentation, enzymes, and organic acids production, anti-fungal activity, antibiotic sensitivity patterns, and probiotic characteristics (acidic and bile salt tolerances, hydrophobicity and aggregations natures) of LAB were examined. 16SrRNA sequencing was carried out to identify isolated strains. The identified strains Lactobacillus plantarum (KCC-37) and Lactobacillus plantarum (KCC-38) showed intense antifungal activity, survival tolerant in acidic and bile salt environments, cell surface and auto aggregations ability, enzymes and organic acids productions. At ensiled condition, KCC-37 and KCC-38 enhanced acidification of Italian ryegrass silages by producing a higher amount of lactic acid, a key acid for indicating silage quality with less extent to acetic acid and succinic acid at low moisture level than non-inoculated silages. Notably, the addition of mixed strains of KCC-37 and KCC-38 more potentially enhanced acidification of silage and organic acid productions than the single-culture inoculation. The overall data suggested that these strains could be used as an additive for improving the quality of the fermentation process in low moisture silage with significant probiotic characteristics.

Is Karenia brevis really a low-light-adapted species?

Despite nearly annual blooms of the neurotoxic dinoflagellate Karenia brevis (Davis) G. Hansen and Moestrup in the Gulf of Mexico, defining the suite of biological traits that explain its proliferation has remained challenging. Studies have described K. brevis as a low-light-adapted species, incapable of sustaining growth under high light, which is at odds with observed surface aggregations sometimes within centimeters of the sea surface and also with short-term experiments showing photosynthetic machinery accommodating high irradiances. Here, growth and photophysiology of three K. brevis isolates were evaluated under a range of environmentally relevant irradiances (10–1500 μmol photons m−2 s−1) in the laboratory. No differences in growth–irradiance curves were observed among isolates; all sustained maximum growth rates at the highest irradiances examined, even in exposures as long as three weeks. The growth efficiency α of K. brevis under light-limiting conditions appeared mediocre among dinoflagellates, and poorer than that of other phytoplankton (e.g., diatoms, cyanobacteria), implying that K. brevis is not a low-light specialist. This finding substantially alters earlier parameterizations of K. brevis growth–irradiance curves. Therefore, a model was developed to contextualize how these new growth–irradiance curves might affect bottom growth rates. This model was subsequently applied to a case study comparing seasonal light forcing offshore of Pinellas County, FL, USA, with a single empirical value for light attenuation, and seasonal bottom water temperatures. Predictions suggested that light may limit bottom growth as close as 1 km from shore in winter, but would only begin limiting growth 20 km from shore in summer. Population maintenance (no net growth) was possible as far offshore as 90 km in summer and 68 km in winter. These ranges intercept areas thought to be important for bloom initiation.

Use of WorldView-2 Along-Track Stereo Imagery to Probe a Baltic Sea Algal Spiral

The general topic here is the application of very high-resolution satellite imagery to the study of ocean phenomena having horizontal spatial scales of the order of 1 kilometer, which is the realm of the ocean submesoscale. The focus of the present study is the use of WorldView-2 along-track stereo imagery to probe a submesoscale feature in the Baltic Sea that consists of an apparent inward spiraling of surface aggregations of algae. In this case, a single pair of images is analyzed using an optical-flow velocity algorithm. Because such image data generally have a much lower dynamic range than in land applications, the impact of residual instrument noise (e.g., data striping) is more severe and requires attention; we use a simple scheme to reduce the impact of such noise. The results show that the spiral feature has at its core a cyclonic vortex, about 1 km in radius and having a vertical vorticity of about three times the Coriolis frequency. Analysis also reveals that an individual algal aggregation corresponds to a velocity front having both horizontal shear and convergence, while wind-accelerated clumps of surface algae can introduce fine-scale signatures into the velocity field. Overall, the analysis supports the interpretation of algal spirals as evidence of a submesoscale eddy and of algal aggregations as indicating areas of surface convergence.

Phenology of Trichodesmium spp. blooms in the Great Barrier Reef lagoon, Australia, from the ESA-MERIS 10-year mission.

Trichodesmium, a filamentous bloom-forming marine cyanobacterium, plays a key role in the biogeochemistry of oligotrophic ocean regions because of the ability to fix nitrogen. Naturally occurring in the Great Barrier Reef (GBR), the contribution of Trichodesmium to the nutrient budget may be of the same order as that entering the system via catchment runoff. However, the cyclicity of Trichodesmium in the GBR is poorly understood and sparsely documented because of the lack of sufficient observations. This study provides the first systematic analysis of Trichodesmium spatial and temporal occurrences in the GBR over the decade-long MERIS ocean color mission (2002–2012). Trichodesmium surface expressions were detected using the Maximum Chlorophyll Index (MCI) applied to MERIS satellite imagery of the GBR lagoonal waters. The MCI performed well (76%), albeit tested on a limited set of images (N = 25) coincident with field measurements. A north (Cape York) to south (Fitzroy) increase in the extent, frequency and timing of the surface expressions characterized the GBR, with surface expressions extending over several hundreds of kilometers. The two southernmost subregions Mackay and Fitzroy accounted for the most (70%) bloom events. The bloom timing of Trichodesmium varied from May in the north to November in the south, with wet season conditions less favorable to Trichodesmium aggregations. MODIS-Aqua Sea Surface Temperature (SST) datasets, wind speed and field measurements of nutrient concentrations were used in combination with MCI positive instances to assess the blooms’ driving factors. Low wind speed (<6 m.s-1) and SST > 24°C were associated with the largest surface aggregations. Generalized additive models (GAM) indicated an increase in bloom occurrences over the 10-year period with seasonal bloom patterns regionally distinct. Interannual variability in SST partially (14%) explained bloom occurrences, and other drivers, such as the subregion and the nutrient budget, likely regulate Trichodesmium surface aggregations in the GBR.

A green and easy synthesis method of catanionic surfactant ammonium benzenesulfonate and its surface properties and aggregation behaviors

Catanionic surfactants play a prominent role in the biotechnology, drag-reduction agents, microreactors and other fields, but the catanionic surfactants are all synthesized from halogenated quaternary ammonium salts or dimethyl sulfated quaternary ammonium salts more or less. In this context, we put forward a new synthetic method without halogenated organics or dimethyl sulfated organics to improve the conventional method. Quite different, a typical catanionic surfactant ammonium benzenesulfonate was synthesized from tertiary amine, dimethyl carbonate and dodecylbenzenesulfonic acid. The structure of the product was established using various techniques, Fourier transform infrared spectroscopy (FT-IR), H-nuclear magnetic resonance (1H NMR), C-nuclear magnetic resonance (13C NMR), and electrospray ionization mass spectrometry (ESI-MS). Also, the surface activities and aggregations of ammonium benzenesulfonate were detected by equilibrium surface tension and dynamic surface tension, contact angle, dynamic light scattering (DLS). Our results provide proofs for the successful synthesis of ammonium benzenesulfonate and the explanations for the surface properties and aggregation behaviors.

Turbulence characteristics inferred from time-lagged satellite imagery of surface algae in a shallow tidal sea

A pair of time-lagged satellite images of surface algae in the Great Barrier Reef lagoon is used to investigate characteristics of the horizontal velocity field at a spatial resolution as small as 4m. A distinctive feature is the occurrence of surface patches that are relatively clear of algae and which grow in size. These patches are interpreted as resulting from the horizontally diverging motion associated with boils. The surface divergence in such boils can be as large as ~ 0.01s−1, as deduced directly from the imagery. Overall, root-mean-squared values of divergence, vorticity, and strain rate are 45, 58, and 170, respectively, when normalized by the Coriolis parameter. By observing the algae and its fluid environment simultaneously, the analysis thus provides a glimpse of how underlying hydrodynamic processes help shape the distribution of surface algae — under the calm winds that favor the formation of dense surface aggregations.

Bloom formation potential in the harmful dinoflagellate Akashiwo sanguinea: Clues from movement behaviors and growth characteristics

We measured the growth rates and swimming behaviors of recently isolated strains of the dinoflagellate Akashiwo sanguinea to investigate to what degree growth and motility could contribute to the formation of in situ blooms. To quantify the effect of variation in in situ conditions on population growth rate, we applied two temperature treatments (10°C and 20°C) and measured growth in still conditions and on a shaker table, to emulate mild turbulence. To quantify the importance of intra-strain variability and trait variation in the species growth potential and vertical distribution, we included six strains isolated from a spatially and temporally extensive bloom on the US West Coast. Overall, as reported previously, A. sanguinea was observed to tolerate conditions amounting to a broad ecological niche with intra-specific variability further broadening tolerable conditions. In agreement with prior observations of slow growth rates of the species, average growth rates across all strains increased significantly from 0.12 d−1 (±0.03) at 10°C to 0.28 d−1 (±0.13) at 20°C in still conditions. Contrary to prior reports, mild turbulence had neutral or positive effects on most strains’ growth rates, with one strain only able to grow on the shaker table. Growth rates in mild turbulence were higher than in still conditions and increased from 0.15 d−1 (±0.01) at 10°C to 0.43 d−1 (± 0.04) at 20°C. There was significant intra-strain variation in growth rates (>50% coefficient of variation) and movement behaviors. All strains had both up and down swimming fractions, leading to predictions of vertically patchy distributions, rather than surface aggregations. Slow growth rates and dispersive swimming behaviors suggest in situ mortality must be low and tolerance of seasonally varying water temperatures lead to accumulation and persistence of cells over months and kilometers. Estimates of in situ loss rates are a critical but missing component of identifying the bloom formation mechanisms of this species.

Unusually High Levels of n‐6 Polyunsaturated Fatty Acids in Whale Sharks and Reef Manta Rays

Fatty acid (FA) signature analysis has been increasingly used to assess dietary preferences and trophodynamics in marine animals. We investigated FA signatures of connective tissue of the whale shark Rhincodon typus and muscle tissue of the reef manta ray Manta alfredi. We found high levels of n-6 polyunsaturated fatty acids (PUFA), dominated by arachidonic acid (20:4n-6; 12–17 % of total FA), and comparatively lower levels of the essential n-3 PUFA—eicosapentaenoic acid (20:5n-3; ~1 %) and docosahexaenoic acid (22:6n-3; 3–10 %). Whale sharks and reef manta rays are regularly observed feeding on surface aggregations of coastal crustacean zooplankton during the day, which generally have FA profiles dominated by n-3 PUFA. The high levels of n-6 PUFA in both giant elasmobranchs raise new questions about the origin of their main food source.

DLC Coating by HiPIMS: The Influence of Substrate Bias Voltage

Carbon-related materials are prepared using various physical vapor deposition (PVD) methods. High-power impulse magnetron sputtering is a PVD method that uses glow plasma and this method is employed to prepare diamond-like carbon (DLC) films. The densities of the glow current and the consumed power for an effective area of plasma generation are 1.4 ${\rm A}/{\rm cm}^{2}$ and 1.2 ${\rm kW}/{\rm cm}^{2}$ , respectively. A pulsed bias is applied to the substrate (subsequently called substrate bias voltage). The pressures of the background gas and the substrate bias voltages influence the surface morphology and the roughness of the deposited films. It is discovered that a critical pressure of 0.3 Pa and a critical bias voltage of ${-}{\rm 100}~{\rm V}$ is needed to change the DLC film characterization. A drastic change in these characteristics is seen for pressures ${ ; a bumping surface and dumpling-like aggregations are produced. In addition, there is a bias-voltage dependency on these films, as smoother surfaces are seen in a bias-voltage range that is higher than ${-}{\rm 100}~{\rm V}$ . This phenomenon may be related to the DLC structure, which is evaluated by Raman parameters of the deposited films. It is found that the position and the full width at half maximum of the graphite peak show a minimum and a maximum, respectively, at a bias voltage of ${-}{\rm 100}~{\rm V}$ . The results of X-ray photoemission spectroscopy reveal that the ${\rm sp}^{3}$ bond ratio indicates a maximum at a pressure of 0.3 Pa and at a bias voltage of ${-}{\rm 100}~{\rm V}$ . Thus, it is clear that the gas pressure of 0.3 Pa and the bias voltage of ${-}{\rm 100}~{\rm V}$ are critical values that change the pressure and bias dependence of the film characteristics.

Fine-scale biophysical interactions drive prey availability at a migratory stopover site for Phalaropus spp. in the Bay of Fundy, Canada

We examined the role of biophysical interactions in structuring the foraging habitat of phalaropes Phalaropus spp. at an important migratory stopover site in the Bay of Fundy. We sampled both biological and physical aspects of the environment and integrated these observa- tions into generalized additive models (GAMs). Strong tidal currents interact with steep bathy- metric gradients at the Brier Island ledges to enhance vertical mixing, creating dense surface aggregations of Calanus finmarchicus copepods at fine temporal and spatial scales. The resulting spatial variation in copepod density in near-surface waters creates a highly heterogeneous foraging environment for phalaropes, which are obligate surface feeders. Models of phalarope abundance over the ledges suggested that phalaropes forage on upwelled zooplankton aggrega- tions as they drifted downstream. Our results highlight the importance of considering underlying physical processes when assessing hotspots of prey aggregations for marine species, particularly within highly dynamic systems such as the Bay of Fundy. This is particularly relevant to consider- ations of the conservation status of red-necked phalaropes Phalaropus lobatus, which have aban- doned a long-time migratory stopover area previously used by more than one million birds during the mid-1980s.

PH alters the swimming behaviors of the raphidophyte Heterosigma akashiwo: Implications for bloom formation in an acidified ocean

We investigated the effects of pH on movement behaviors of the harmful algal bloom causing raphidophyte Heterosigma akashiwo. Motility parameters from >8000 swimming tracks of individual cells were quantified using 3D digital video analysis over a 6-h period in 3 pH treatments reflecting marine carbonate chemistry during the pre-industrial era, currently, and the year 2100. Movement behaviors were investigated in two different acclimation-to-target-pH conditions: instantaneous exposure and acclimation of cells for at least 11 generations. There was no negative impairment of cell motility when exposed to elevated PCO2 (i.e., low pH) conditions but there were significant behavioral responses. Irrespective of acclimation condition, lower pH significantly increased downward velocity and frequency of downward swimming cells (p<0.001). Rapid exposure to lower pH resulted in 9% faster downward vertical velocity and up to 19% more cells swimming downwards (p<0.001). Compared to pH-shock experiments, pre-acclimation of cells to target pH resulted in ~30% faster swimming speed and up to 46% faster downward velocities (all p<0.001). The effect of year 2100 PCO2 levels on population diffusivity in pre-acclimated cultures was >2-fold greater than in pH-shock treatments (2.2×105μm2s−1 vs. 8.4×104μm2s−1). Predictions from an advection-diffusion model, suggest that as PCO2 increased the fraction of the population aggregated at the surface declined, and moved deeper in the water column. Enhanced downward swimming of H. akashiwo at low pH suggests that these behavioral responses to elevated PCO2 could reduce the likelihood of dense surface slick formation of H. akashiwo through reductions in light exposure or growth independent surface aggregations. We hypothesize that the HAB alga's response to higher PCO2 may exploit the signaling function of high PCO2 as indicative of net heterotrophy in the system, thus indicative of high predation rates or depletion of nutrients.