Characteristics of glottis-induced turbulence in oscillatory flow: an empirical investigation.

Turbulence inducement from the glottis was scrutinized by employing an idealized model of the larynx and trachea for oscillatory flow conditions. The characterization of turbulence was achieved with the two-component velocity measurements of split-film probe anemometry and with the flow visualization of a smoke-wire technique. The apertures of two different (triangular and circular) shapes were utilized in the airway model to address the distinct effects of the triangular-shaped glottal aperture on the generation, development, and decay of turbulence. One of the salient turbulence characteristics for the triangular aperture case was found to be the relatively high turbulence levels around the center region (2r/D approximately 0) in conjunction with the asymmetric mean axial velocity across the frontal-rear (A-O-P) plane of the trachea at one tracheal diameter (x/D = 1) downstream from the glottis. The detailed turbulence properties such as the Reynolds shear stresses and turbulence intensities for the triangular aperture case differed significantly from those for the circular aperture case within a few tracheal diameters (x/D < 7) downstream from the apertures. The glottis-induced turbulence was incipient during the acceleration phase of inspiration and convected downstream with the traits of decaying turbulence.     

Vertical distribution and feeding of larval blue whiting in turbulent waters above Porcupine Bank

In April 1995 a patch of blue whiting larvae Micromesistius poutassou was found at low illumination levels below 20 m depth near Porcupine Bank, west of Ireland, together with high densities of copepod nauplii and reduced turbulence rates, suggesting that larval blue whiting vertical distribution was determined by prey concentration, illumination and turbulence. Most (83·8%) larvae (2·0–7·5 mm L _s) had food in their guts. Feeding incidence and feeding intensities increased with increasing larval length. Only larvae >5·5 mm reduced numerical in favour of weight-based feeding intensity, indicating a shift in dietary composition. Maxima of the diel rhythms of feeding incidence and intensities occurred at 1800 and 2100 hours and minima at dawn (0600 hours). Proportionately, more nauplii were eaten by day but more copepod eggs and tintinnids at night. The distinct diel pattern in larval blue whiting feeding suggests that any analysis of factors mediating feeding must take into account diel feeding cycles. Larval feeding was significantly affected by wind speed. The larvae ate more and larger items at low than at higher turbulence levels. The data suggest that the maximum level of turbulence was not beneficial for larval blue whiting, but more moderate wind speeds could have had an enhancing effect on larval feeding success.     

The influence of experimentally generated turbulence on the Mash01 unicellular Microcystis aeruginosa strain

Phytoplankton experience a continuously changing fluid environment and the response to this is reflected at individual and community levels. The large-scale motions of winds, waves and artificial circulations are coupled by turbulence to the viscous small-scale environment of the phytoplankton cell. To investigate the significance of turbulence in the ecology of Microcystis aeruginosa, cultures were exposed to turbulent conditions using a vertically oscillating grid for a period of 7 days under controlled laboratory conditions. M. aeruginosa was exposed to a range of turbulent intensities, by adjusting the frequency of oscillation from 1 to 4 Hz. To improve the resolution of scale between turbulence phenomena and phytoplankton, flow cytometry and fluorescent probes were used to assess the response of M. aeruginosa. Metabolic activity and cell viability were monitored daily in both the turbulent cultures and quiescent control cultures using the FDA and Sytox green fluorescent probes, respectively. Initially, low turbulence levels generated by the grid at frequencies of 1 and 2 Hz stimulated metabolic activity, and did not affect cell viability compared to the control quiescent cultures. However, higher levels of turbulence generated by the grid at frequencies of 3 and 4 Hz were deleterious to metabolic activity and viability. Metabolic activity significantly decreased and over 85 % of cells were nonviable after 96 h at a grid oscillation of 4 Hz. It was concluded that due to the long lag time (>96 h) and high intensities needed to exert a deleterious effect, small-scale turbulence is unlikely to be a significant factor controlling M. aeruginosa compared to large scale motion which lead to changes in light and nutrient conditions.     

Turbulent shear stress measurements in the vicinity of aortic heart valve prostheses

A two dimensional laser Doppler anemometer system has been used to measure the turbulent shear fields in the immediate downstream vicinity of a variety of mechanical and bioprosthetic aortic heart valves. The measurements revealed that all the mechanical valves studied, created regions of elevated levels of turbulent shear stress during the major portion of systole. The tissue bioprostheses also created elevated levels of turbulence, but they were confined to narrow regions in the bulk of the flow field. The newer generation of bioprostheses create turbulent shear stresses which are considerably lower than those created by the older generation tissue valve designs. All the aortic valves studied (mechanical and tissue) create turbulent shear stress levels which are capable of causing sub-lethal and/or lethal damage to blood elements.     

In vivo demonstration of flow recirculation and turbulence downstream of graded stenoses in canine arteries

The velocity field around arterial stenoses was investigated using a pulsed doppler velocimeter in vivo. Asymmetric zones of recirculation were identified by systolic flow reversal in the post-stenotic field in carotid and iliac arteries of anesthetised dogs. There was a close correlation between shear intensity and turbulence as estimated by the velocity difference between the jet and the recirculation zone and by maximum spectral width respectively. Under the conditions of these experiments, stenosis grade (% diameter reduction) dominated hemodynamic variables such as Reynolds number, oscillation and pulsatility in determining the intensity of turbulence. The method used does not appear to have sufficient resolution to distinguish between turbulence and discrete oscillating velocities (vorticity) nor to allow determination of wall shear stress though the pattern of change of the latter is similar to that found downstream of axisymmetric stenosis in models using steady flow.     

Effects of small-scale turbulence on feeding rate and gross-growth efficiency of three Acartia species (Copepoda: Calanoida)

Experiments designed to test the effects of small-scale turbulenceon the feeding rates and gross-growth efficiency of calanoidcopepods have been performed within a wide range of controlledfood concentrations. Turbulence significantly enhanced feedingrates only at food concentrations lower than the ingestion saturatinglevel. Gross-growth efficiency (the quotient carbon-egg production/carbon-foodingested) of the different Acartia species studied showed differentpatterns of response to turbulence, in agreement with the hydrodynamiccharacteristics of their habitat. Furthermore, experiments conductedon Acartia clausi at two different intensities of turbulenceindicate a shift in the response, with enhancement of feedingat low intensities of turbulence and negative interference athigher intensities.     

Causes of shear sensitivity of the toxic dinoflagellate Protoceratium reticulatum

Dinoflagellates have proven extremely difficult to culture because they are inhibited by low‐level shear forces. Specific growth rate of the toxic dinoflagellate Protoceratium reticulatum was greatly decreased compared with static control culture by intermittent exposure to a turbulent hydrodynamic environment with a bulk average shear rate that was as low as 0.3 s^?1. Hydrodynamic forces appeared to induce the production of reactive oxygen species (ROS) within the cells and this caused peroxidation of cellular lipids and ultimately cell damage. Exposure to damaging levels of shear rate correlated with the elevated level of lipoperoxides in the cells, but ROS levels measured directly by flow cytometry did not correlate with shear induced cell damage. This was apparently because the measured level of ROS could not distinguish between the ROS that are normally generated by photosynthesis and the additional ROS produced as a consequence of hydrodynamic shear forces. Continuously subjecting the cells to a bulk average shear rate value of about 0.3 s^?1 for 24‐h caused an elevation in the levels of chlorophyll a, peridinin and dinoxanthin, as the cells apparently attempted to counter the damaging effects of shear fields by producing pigments that are potential antioxidants. In static culture, limitation of carbon dioxide produced a small but measureable increase in ROS. The addition of ascorbic acid (0.1 mM) to the culture medium resulted in a significant protective effect on lipid peroxidation, allowing cells to grow under damaging levels of shear rates. This confirmed the use of antioxidant additives as an efficient strategy to counter the damaging effects of turbulence in photobioreactors where shear sensitive dinoflagellates are cultivated. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2009     

Colon cancer cell adhesion in response to Src kinase activation and actin-cytoskeleton by non-laminar shear stress

Malignant cells shed from tumors during surgical resection or spontaneous metastasis experience physical forces such as shear stress and turbulence within the peritoneal cavity during irrigation, laparoscopic air insufflation, or surgical manipulation, and within the venous or lymphatic system. Since physical forces can activate intracellular signals that modulate the biology of various cell types in vitro, we hypothesized that shear stress and turbulence might increase colon cancer cell adhesion to extracellular matrix, potentiating metastatic implantation. Primary human malignant colon cancer cells isolated from resected tumors and SW620 were subjected to shear stress and turbulence by stirring cells in suspension at 600 rpm for 10 min. Shear stress for 10 min increased subsequent SW620 colon cancer cell adhesion by 40.0 +/- 3.0% (n = 3; P < 0.001) and primary cancer cells by 41.0 +/- 3.0% to collagen I when compared to control cells. In vitro kinase assay (1.5 +/- 0.13 fold) and Western analysis (1.34 +/- 0.04 fold) demonstrated a significant increase in Src kinase activity in cells exposed shear stress. Src kinase inhibitors PP1 (0.1 microM), PP2 (20 microM), and actin-cytoskeleton stabilizer phalloidin (10 microM) prevented the shear stress stimulated cell adhesion to collagen I. Furthermore, PP2 inhibited basal (50.0 +/- 2.8%) and prevented shear stress induced src activation but phalloidin pretreatment did not. These results raise the possibility that shear stress and turbulence may stimulate the adhesion of malignant cells shed from colon cancers by a mechanism that requires both actin-cytoskeletal reorganization an independent physical force activation of Src kinase. Blocking this pathway might reduce tumor metastasis during surgical resection.     

MECHANISMS OF FLUID SHEAR‐INDUCED INHIBITION OF POPULATION GROWTH IN A RED‐TIDE DINOFLAGELLATE1

Net population growth of some dinoflagellates is inhibited by fluid shear at shear stresses comparable with those generated during oceanic turbulence. Decreased net growth may occur through lowered cell division, increased mortality, or both. The dominant mechanism under various flow conditions was determined for the red‐tide dinoflagellate Lingulodinium polyedrum (Stein) Dodge. Cell division and mortality were determined by direct observation of isolated cells in 0.5‐mL cultures that were shaken to generate unquantified fluid shear. Larger volume cultures were exposed to quantified laminar shear in Couette‐flow chambers (0.004–0.019 N·m ^{? 2} shear stress) and to unquantified flow in shaken flasks. In these larger cultures, cell division frequency was calculated from flow cytometric measurements of DNA·cell^?1. The mechanism by which shear inhibits net growth of L. polyedrum depends on shear stress level and growth conditions. Observations on the isolated cells showed that shaking inhibited growth by lowering cell division without increased mortality. Similar results were found for early exponential‐phase cultures exposed to the lowest experimental shear stress in Couette‐flow chambers. However, mortality occurred when a late exponential‐phase culture was exposed to the same low shear stress and was inferred to occur in cultures exposed to higher shear stresses. Elevated mortality in those treatments was confirmed using behavioral, morphological, and physiological assays. The results predict that cell division in L. polyedrum populations will be inhibited by levels of oceanic turbulence common for near‐surface waters. Shear‐induced mortality is not expected unless shear‐stress levels are unusually high or when cellular condition resembles late exponential/stationary phase cultures.     

EFFECTS OF SMALL-SCALE TURBULENCE ON PHOTOSYNTHESIS,PIGMENTATION, CELL DIVISION,AND CELL SIZE IN THE MARINE DINOFLAGELLATE GOMAULAX POLYEDRA (DINOPHYCEAE)1

Several experiments were conducted to understand better the physiological mechanisms underlying growth inhibition of the dinoflagellate Gonyaulax polyedra Stein due to small-scale turbulence shear. To measure photosynthetic ¹⁴C uptake, a “phytoplankton wheel” device for rotating cultures in closed bottles was used. Turbulence was quantified biologically in the bottles by comparing growth inhibition with that in cultures with constant shear between a fixed cylinder and an outer concentric rotating cylinder (a stable Couette flow). At saturating irradiances, particulate photosynthesis (P_sat) or photosynthesis per unit chlorophyll (P^B_sat) were not inhibited completely at the highest turbulence level (26.6 rad.s^?1), and photosynthesis was less sensitive than growth. Photosynthesis per cell (P^C_sat) was increased by turbulence. In three experiments on the effects of turbulence on photosynthesis versus irradiance curves, the slope of the curve, α, for particulate photosynthesis at limiting irradiances did not change. Photosynthesis per unit chlorophyll per unit irradiance (α^B) decreased at high (but not intermediate) turbulence levels. Photosynthesis per cell per unit irradiance, α^C, increased with turbulence, suggesting an increase in photosynthetic efficiency in turbulent cultures. In two of the three experiments, respiration rates increased with turbulence, and in one experiment excretion of photosynthetically fixed ¹⁴C was not affected by motion. Ratios of accessory pigments to chlorophyll a did not change with turbulence, but pigments per cell and per dry weight increased with turbulence. These findings suggest little or no disruption of the photosynthetic apparatus. When turbulence was applied for 1 week, β-carotene increased while peridinin and diadinoxanthin decreased, suggesting inhibition of synthesis of these latter pigments by prolonged turbulence. Since cell numbers did not increase or decreased during turbulent 72–h incubations, cell division was inhibited and also the cells were very much enlarged. Increases in α^C per cell suggest that, in the sea, photo synthetic metabolism can persist efficiently without cell division during turbulent episodes. After turbulence ceases or reaches low levels again, cells can then divide and blooms may form. Thus, blooms can come or go fairly rapidly in the ocean depending on the degree of wave- and wind-induced turbulence.     

Effect of larval ontogeny, turbulence and light on prey attack rate and swimming activity in herring larvae

The effects of ontogeny (larval size), light and turbulence on the attack rate and swimming activity (proportion of time swimming and duration of swimming bout) of herring larvae (15-28 mm TL) have been investigated. Emphasis was put on the experimental design in order to create a set-up where the turbulence intensity distribution could be accurately measured as well as controlled in the entire experimental tank.Both larval size (ontogeny) and light had a significant positive effect on prey attack rate. Likewise, an intermediate increase in turbulence had a positive effect on prey attack rate, but this effect was dependent of light intensity and larval size.At low light (1.5 μE m² s⁻¹) intermediate turbulence increased the prey attack rate significantly for larger larvae (26 and 28 mm), while at high light (18 μE m² s⁻¹) intermediate turbulence had only a significant positive effect on the attack rate of smaller larvae 20 and 23 mm.In general, our data show a dome-shaped response of turbulence on attack rate and a U-shaped response of turbulence on swimming activity.For herring larvae >20 mm, the maximum (attack rate) and minimum (swimming activity) response of turbulence were found at intermediate turbulence intensities (energy dissipation rates between 7∗10⁻⁸ and 1∗10⁻⁶ W/kg). The highest turbulence level tested (8∗10⁻⁶ W/kg) showed only negative effects, as attack rates where at the lowest and swimming activity at the highest.Swimming activity increased with larval size or light, and decreased at intermediate turbulence. Compared to turbulent intensities under natural conditions this implies that larger herring larvae at 10 m depth have to be exposed to wind speeds of more than 17 m/s before negative effects on attack rate and swimming activity occurs.     

Terpene production and growth of three Pacific Northwest conifers in response to simulated browse and nutrient availability

Natural variation in ungulate browsing behavior interferes with the understanding of plant morphological and biochemical responses to herbivory. To investigate mechanisms for recovery from herbivory, we examined growth patterns and biosynthesis of terpenoids under simulated browse (three clipping intensities) and supplemental mineral nutrition (four levels of controlled-release fertilization) for Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco], western hemlock (Tsuga heterophylla Raf. Sarg.), and western red-cedar (Thuja plicata Donn ex D. Don) seedlings on a reforestation site in Northwestern Oregon, USA, that was fenced to exclude ungulates. Higher clipping intensities increased relative height growth (at cost of diameter growth) for all the species. Only western red-cedar showed a decline in monoterpene concentrations with increasing clipping severity, suggesting prioritization in biosynthesis of terpenoids for this species. Douglas-fir and western hemlock responded to fertilization mostly through increased growth. Western red-cedar growth responses to fertilization were less pronounced, but monoterpene concentrations were 2–3 times higher compared to non-fertilized trees. Douglas-fir and western hemlock browse recovery and responses to fertilization consisted primarily of increased growth, while western red-cedar balanced growth promotion with production of chemical defense compounds. Our data suggests the evolution of species-dependent resource allocation strategies in response to both browse and soil nutrient availability.     

Factors influencing the nonrandom abscission of Solidago canadensis seeds

 为揭示加拿大一枝黄花(Solidago canadensis)种群扩散机制, 明确种子的脱落及风传扩散在其种群蔓延中的作用, 在人工环境下测定了不同湍流强度、风速和湿度处理下种子脱落的差异, 并对脱落种子与未脱落种子进行形态学特征对比。结果表明: 加拿大一枝黄花的种子脱落受湍流、风速和湿度等因素的共同影响。水平气流下种子的脱落阈值为5.1 m·s^–1, 并随着风速增加, 种子的脱落率增加。与模拟水平气流相比, 模拟垂直气流下种子的脱落阈值显著偏小。相对于层流状态, 湍流的存在显著提高了种子的脱落率, 平均增幅超过300%; 但单纯提高湍流强度对种子脱落率的影响不显著。增加湿度则显著降低种子的脱落率。种子形态学特征对比结果表明, 脱落种子的冠毛数量和冠毛夹角显著高于未脱落种子。该研究结果为研究加拿大一枝黄花种子脱落规律和风传扩散机制提供了科学依据, 也为其他入侵性杂草种子的扩散机制及入侵过程提供了借鉴。     

A turbulence model for pulsatile arterial flows

Difficulties in predicting the behavior of some high Reynolds number flows in the circulatory system stem in part from the severe requirements placed on the turbulence model chosen to close the time-averaged equations of fluid motion. In particular, the successful turbulence model is required to (a) correctly capture the "nonequilibrium" effects wrought by the interactions of the organized mean-flow unsteadiness with the random turbulence, (b) correctly reproduce the effects of the laminar-turbulent transitional behavior that occurs at various phases of the cardiac cycle, and (c) yield good predictions of the near-wall flow behavior in conditions where the universal logarithmic law of the wall is known to be not valid. These requirements are not immediately met by standard models of turbulence that have been developed largely with reference to data from steady, fully turbulent flows in approximate local equilibrium. The purpose of this paper is to report on the development of a turbulence model suited for use in arterial flows. The model is of the two-equation eddy-viscosity variety with dependent variables that are zero-valued at a solid wall and vary linearly with distance from it. The effects of transition are introduced by coupling this model to the local value of the intermittency and obtaining the latter from the solution of a modeled transport equation. Comparisons with measurements obtained in oscillatory transitional flows in circular tubes show that the model produces substantial improvements over existing closures. Further pulsatile-flow predictions, driven by a mean-flow wave form obtained in a diseased human carotid artery, indicate that the intermittency-modified model yields much reduced levels of wall shear stress compared to the original, unmodified model. This result, which is attributed to the rapid growth in the thickness of the viscous sublayer arising from the severe acceleration of systole, argues in favor of the use of the model for the prediction of arterial flows.     

A discussion on the threshold limit for hemolysis related to Reynolds shear stress.

Turbulence-related damage to blood is a major problem with the use of prosthetic devices, such as mechanical heart valves. An often-cited paper by Sallam and Hwang (1984). Biorheology 21, 783-797) quantified the threshold for hemolysis to be about 400 N m(-2), a value that has hitherto contributed to the evaluation of the potential dangerousness of a medical implantable device. We propose a discussion of the mentioned experiment, based on the application of stress analysis concepts to the original measurements: this is necessary to assess the peak turbulence shear stress value that could have been found in Sallam and Hwangs experiment, with a suitable orientation of the measurement axes. The result of our theoretical discussion is that the threshold value of 400 N m(-2) could probably be considerably underestimated: following this point of view, a 3-D stress analysis shows that the peak turbulence shear stress at the inception of hemolysis should be at least 600 N m(-2). This result, obtained on the basis of the study of RBCs' response to a turbulent environment, indicates that blood particles are probably more resistant to short-time shear stresses than it was thought.     

Turbulence modeling in three-dimensional stenosed arterial bifurcations

Under normal healthy conditions, blood flow in the carotid artery bifurcation is laminar. However, in the presence of a stenosis, the flow can become turbulent at the higher Reynolds numbers during systole. There is growing consensus that the transitional k-omega model is the best suited Reynolds averaged turbulence model for such flows. Further confirmation of this opinion is presented here by a comparison with the RNG k-epsilon model for the flow through a straight, nonbifurcating tube. Unlike similar validation studies elsewhere, no assumptions are made about the inlet profile since the full length of the experimental tube is simulated. Additionally, variations in the inflow turbulence quantities are shown to have no noticeable affect on downstream turbulence intensity, turbulent viscosity, or velocity in the k-epsilon model, whereas the velocity profiles in the transitional k-omega model show some differences due to large variations in the downstream turbulence quantities. Following this validation study, the transitional k-omega model is applied in a three-dimensional parametrically defined computer model of the carotid artery bifurcation in which the sinus bulb is manipulated to produce mild, moderate, and severe stenosis. The parametric geometry definition facilitates a powerful means for investigating the effect of local shape variation while keeping the global shape fixed. While turbulence levels are generally low in all cases considered, the mild stenosis model produces higher levels of turbulent viscosity and this is linked to relatively high values of turbulent kinetic energy and low values of the specific dissipation rate. The severe stenosis model displays stronger recirculation in the flow field with higher values of vorticity, helicity, and negative wall shear stress. The mild and moderate stenosis configurations produce similar lower levels of vorticity and helicity.     

Augmentation of sickling process due to turbulent blood flow.

The purpose of this study was to determine if the fluid mechanical stresses associated with turbulent blood flow can contribute to the sickling process. Blood from seven patients with sickle cell disease was subjected to intermediate and high levels of turbulent flow in vitro. Turbulence was quantitated by hot film anemometry. Control samples showed 20 +/- 3% sickled cells. Cells subjected to intermediate levels of turbulent flow showed 26 +/- 4% sickling (P less than 0.01); and blood subjected to high intensities of turbulence showed 31 +/- 4% sickling (P less than 0.01). A quantitative count by electronmicroscopy, performed in one patient, showed polymerization of the hemoglobin indicative of sickling in more cells subjected to turbulence than in the control sample. A turbulence-reducing agent, polyethylene oxide, diminished the augmentation of the sickling process as it reduced turbulence at comparable Reynolds numbers. These results support the hypothesis that a deleterious effect upon hemoglobin SS erythrocytes may occur due to the mechanical stresses of turbulent flow. The agitation associated with turbulent flow presumably modifies the stabilizing factors of the intracellular colloidal solution of hemoglobin, thereby contributing to sol-gel transformation. Such hydrodynamic stresses may supplement the previously described factors which contribute to sickle cell crises.     

Effects of Small-Scale Turbulence on Bacteria: A Matter of Size

We examined the influence of small-scale turbulence and its associated shear on bacterioplankton abundance and cell size. We incubated natural microbial assemblages and bacteria-only fractions and subjected them to treatments with turbulence and additions of mineral nutrients and/or organic carbon. Bacterial abundance was not affected directly by turbulence in bacteria-only incubations. In natural microbial assemblage incubations, bacterial concentrations were higher under turbulence than in still-water controls when nutrients were added. In general, in the turbulence treatments bacteria increased significantly in size, mainly due to elongation of cells. The addition of inorganic nutrients had a negative effect on bacterial size, but a significantly positive effect on abundance independently of other factors such as turbulence and the presence of predators. Flagellate grazing did not trigger an increase in bacterial size as a grazing resistance response in unmixed containers. With the addition of organic carbon, bacteria elongated and partly settled to the bottom of the containers, in both the turbulent and still treatment, but bacterial abundance did not further increase. Furthermore, bacteria aggregated in the turbulence treatments after the second day of incubation even in the absence of other components of the microbial community. We found that turbulence and the associated shear increase bacterial size and change bacterial morphology, at least under certain nutrient conditions. This might be due to a physiological response (enhanced growth rate and/or unbalanced growth) or due to the selection of opportunistic strains when organic carbon is in excess compared to mineral nutrients. We suggest that shear associated with turbulent flow enhances the DOM flux to bacteria directly as well as indirectly through enhanced grazing activity and photosynthetic release. The formation of bacterial aggregates and filaments under turbulence might give selective advantage to bacteria in terms of nutrient uptake and grazing resistance.     

Elevated pCO2 increases sperm limitation and risk of polyspermy in the red sea urchin Strongylocentrotus franciscanus

Anthropogenic carbon dioxide (CO₂) emissions and the resultant acidification of surface ocean waters are predicted to have far‐reaching consequences for biological processes in the marine environment. For example, because changes in pH and pCO₂ can alter sperm performance, ocean acidification may be accompanied by reductions in the success of fertilization in marine broadcast spawners. Several studies have attempted to determine the effects of elevated pCO₂ on marine invertebrate fertilization success, albeit with differing results. These conflicts may stem from the use of inappropriate sperm–egg contact times and, in several cases, the lack of measurements over a range of sperm concentrations extending from sperm‐limited conditions to polyspermy scenarios. In our study, we used biologically realistic sperm–egg contact times and a full range of sperm concentrations to assess the effect of elevated pCO₂ on fertilization in the broadcast spawning sea urchin, Strongylocentrotus franciscanus. Fertilization experiments were carried out in seawater bubbled with CO₂ to 400 (control), 800, and 1800 ppm. Using a fertilization kinetics model, we estimate that elevated pCO₂ levels both increased sperm limitation and reduced the efficiency of fast blocks to polyspermy. Thus, elevated pCO₂ decreased the range of sperm concentrations over which high fertilization success was likely. Given the inherent difficulties in achieving high fertilization success in broadcast spawners, raised pCO₂ levels are likely to exacerbate low fertilization success in low‐density populations or in areas with high water turbulence.     

Effects of episodic turbulence on diatom mortality and physiology,with a protocol for the use of Evans Blue stain for live–dead determinations

Short-lived, high-intensity turbulence in aquatic environments—or episodic turbulence—has been shown to cause mortality in zooplankton, but its effects on marine phytoplankton have rarely been investigated. Episodic turbulence derives from anthropogenic and natural causes such as boat propellers, strong winds, and breaking waves. This study focused on the effects of episodic turbulence on two diatoms: Thalassiosira weissflogii and Skeletonema costatum. 45 s exposure to turbulence intensities above 2.5 cm² s^?3 reduced diatom abundance by up to 32% and increased the number of intact dead cells by 22%. After exposure to 4.0 cm² s^?3, photosynthetic efficiency decreased by 25 and 9% in T. weissflogii and S. costatum, respectively. Turbulence also caused extracellular release of optically reactive DOM and biologically important trace metals such as iron. The turbulence levels tested are comparable to those under breaking surface waves and are substantially lower than those generated by boat propellers. An improved technique using the Evans Blue stain was developed to enable visual live/dead plankton cell determinations. When used in conjunction with preservation and flow cytometry, this staining method provides a way to study phytoplankton mortality due to turbulence and other environmental stresses.