Critical Threshold Value Research Articles

Chloride levels increase after 13 years of recycled water use in the Salinas Valley

The use of recycled water for agriculture is a long-term water strategy in California. A study in the 1980s in Monterey County showed recycled water increased soil salinity but not to a level unacceptable for agriculture. Most growers in the northern Salinas Valley have been using it since 1998, and yet providers of the water and many growers are concerned that the sustained use of recycled water might cause deterioration of the soil. An ongoing study, initiated in 2000, compares the changes in soil salinity between a field receiving only well water and eight fields that receive recycled water. In 13 years of data, the average soil salinity parameters at each site were highly correlated with the average water quality values of the recycled water. Soil salinity did increase, though not deleteriously. Of most concern was the accumulation of chloride at four of the sites, to levels above the critical threshold values for chloride-sensitive crops.

Determination of Maximum Mechanical Energy Efficiency in Energy Galloping Systems

Transverse galloping is a type of aeroelastic instability characterized by large amplitude, low frequency, normal to wind oscillations that appear in some elastic two-dimensional bluff bodies when subjected to a fluid flow, provided that the flow velocity exceeds a threshold critical value. Such an oscillatory motion is explained because of the energy transfer from the flow to the two-dimensional bluff body. The amount of energy that can be extracted depends on the cross section of the galloping prism. Assuming that the Glauert–Den Hartog quasi-static criterion for galloping instability is satisfied in a first approximation, the suitability of a given cross section for energy harvesting is evaluated by analyzing the lateral aerodynamic force coefficient, fitting a function with a power series in tan⁡α (α being the angle of attack) to available experimental data. In this paper, a fairly large number of simple prisms (triangle, ellipse, biconvex, and rhombus cross sections, as well as D-shaped bodies) is analyzed for suitability as energy harvesters. The influence of the fitting process in the energy harvesting efficiency evaluation is also demonstrated. The analysis shows that the more promising bodies are those with isosceles or approximate isosceles cross sections.

Quantitative assessment of emphysematous parenchyma using multidetector-row computed tomography in patients scheduled for endobronchial treatment with one-way valves†.

To investigate the role of volume quantitative assessment using multidetector-row computed tomography to select patients scheduled for endobronchial one-way valves treatment. Twenty-five consecutive patients (15 with heterogeneous emphysema and 10 with giant emphysematous bulla) undergoing endobronchial valves treatment were enrolled. All patients were studied pre- and postoperatively with standard pulmonary functional tests and quantitative volume assessment of target lobe and entire lung. Emphysematous parenchyma was obtained applying density thresholds of -1.024/-950 Hounsfield units. Among different subtype of patients, we evaluated: (i) the differences between preoperative versus postoperative data; (ii) the correlation between functional and volumetric quantification changes and (iii) the critical threshold value of volumetric quantification of the target lobe in close association with clinical effects. Among heterogeneous emphysematous and giant emphysematous bulla patients, a significant improvement of flow-expiratory volume in 1 s (from 36.9 ± 15.3 to 43.9 ± 10.4; P = 0.01; and from 35.8 ± 6.0 to 47.5 ± 7.9; P < 0.0001, respectively); and of forced vital capacity (from 41.9 ± 5.9 to 47.3 ± 9.3; P = 0.0009 and from 40.7 ± 5.9 to 48.8 ± 4.9; P = 0.0002, respectively); and a significant reduction of residual volume (from 185 ± 14 to 157 ± 14.7; P = 0.005; and from 196 ± 13.5 to 137 ± 21; P < 0.0001, respectively) and of total lung volume (from 166.7 ± 13 to 137 ± 18 ; P = 0.0003, and from 169 ± 15 to 134 ± 18; P < 0.0001, respectively) were seen after treatment. The volumetric measurements showed a reduction of volume of the treated lobe among heterogeneous emphysematous patients (from 1448 ± 204 to 1076 ± 364; P = 0.0008); and in those with giant emphysematous bulla (from 1668 ± 140 to 864 ± 199; P < 0.0001). The entire lung and target lobe volume changes were inversely correlated with change in forced expiratory volume in 1 s in patients with heterogeneous emphysematous (r = -0.7; P = 0.0006; and r = -0.7; P = 0.0009, respectively) and giant emphysematous bulla (r = -0.8; P = 0.001; and r = -0.7; P = 0.009, respectively). Among patients with heterogenous emphysematous and giant emphysematous bulla, the value of sensitivity and specificity were 66.6 and 83%, respectively (for a volumetric qunatification >1.5239), and of 60 and 100%, respectively (for a volumetric qunatification >1.762). Our study showed that the volumetric quantification adds further informations to the routine evaluation for optimizing the selection of patients scheduled for endobronchial valve treatment.

Modeling of the blood rheology in steady-state shear flows

We undertake here a systematic study of the rheology of blood in steady-state shear flows. As blood is a complex fluid, the first question that we try to answer is whether, even in steady-state shear flows, we can model it as a rheologically simple fluid, i.e., we can describe its behavior through a constitutive model that involves only local kinematic quantities. Having answered that question positively, we then probe as to which non-Newtonian model best fits available shear stress vs shear-rate literature data. We show that under physiological conditions blood is typically viscoplastic, i.e., it exhibits a yield stress that acts as a minimum threshold for flow. We further show that the Casson model emerges naturally as the best approximation, at least for low and moderate shear-rates. We then develop systematically a parametric dependence of the rheological parameters entering the Casson model on key physiological quantities, such as the red blood cell volume fraction (hematocrit). For the yield stress, we base our description on its critical, percolation-originated nature. Thus, we first determine onset conditions, i.e., the critical threshold value that the hematocrit has to have in order for yield stress to appear. It is shown that this is a function of the concentration of a key red blood cell binding protein, fibrinogen. Then, we establish a parametric dependence as a function of the fibrinogen and the square of the difference of the hematocrit from its critical onset value. Similarly, we provide an expression for the Casson viscosity, in terms of the hematocrit and the temperature. A successful validation of the proposed formula is performed against additional experimental literature data. The proposed expression is anticipated to be useful not only for steady-state blood flow modeling but also as providing the starting point for transient shear, or more general flow modeling.

Percolation behavior of polymer/metal composites on modification of filler

Polymer–metal composites with different fillers, such as nanocrystalline nickel (n- Ni ), core shell n- Ni and nickel oxide ( NiO )[n- Ni@NiO ] were prepared under the same processing conditions with polyvinyledene fluoride matrix. The larger value of critical exponents (s and s') and percolation threshold (fc~ 0.30) for n- Ni@NiO composites as compared to n- Ni composites (fc~ 0.07) and a comparable effective dielectric constant (εeff~ 300) with low loss tangent ( t an δ ~ 0.1) at 100 Hz in case of percolative n- Ni@NiO composite was observed. The core shell structure [n- Ni@NiO ] also shows a very high value of εeff~ 6000 with tan δ ~ 8 at 40 Hz. The results have been explained by using boundary layer capacitor effect and the percolation theory. The difference in fcand critical exponents is attributed to NiO insulating layer that gives rise to different extent of continuumness at fcand have been explained with the help of Swiss cheese model.

Transverse galloping of two-dimensional bodies having a rhombic cross-section

Transverse galloping is a type of aeroelastic instability characterized by oscillations perpendicular to wind direction, large amplitude and low frequency, which appears in some elastic two-dimensional bluff bodies when they are subjected to an incident flow, provided that the flow velocity exceeds a threshold critical value. Understanding the galloping phenomenon of different cross-sectional geometries is important in a number of engineering applications: for energy harvesting applications the interest relies on strongly unstable configurations but in other cases the purpose is to avoid this type of aeroelastic phenomenon. In this paper the aim is to analyze the transverse galloping behavior of rhombic bodies to understand, on the one hand, the dependence of the instability with a geometrical parameter such as the relative thickness and, on the other hand, why this cross-section shape, that is generally unstable, shows a small range of relative thickness values where it is stable. Particularly, the non-galloping rhombus-shaped prism’s behavior is revised through wind tunnel experiments. The bodies are allowed to freely move perpendicularly to the incoming flow and the amplitude of movement and pressure distributions on the surfaces is measured.

Kinetic Monte Carlo Simulation of the oscillatory catalytic CO oxidation using a modified Ziff-Gulari-Barshad model

The oxidation of CO on Pt-group metal surfaces has attracted widespread attention since a long time due to its interesting oscillatory kinetics and spatiotemporal behavior. The use of STM in conjunction with other experimental data has confirmed the validity of the surface reconstruction (SR) model under low pressure and the more recent surface oxide (SO) model which is possible under sub-atmospheric pressure conditions [1]. In the SR model the surface is periodically reconstructed below a certain low critical CO-coverage and this reconstruction is lifted above a second, higher critical CO-coverage. Alternatively the SO model proposes periodic switching between a low-reactivity metallic surface and a high-reactivity oxide surface. Here we present an overview of our recent kinetic Monte Carlo (KMC) simulation studies on the oscillatory kinetics of surface catalyzed CO oxidation. Different modifications of the lattice gas Ziff-Gulari-Barshad (ZGB) model have been utilized or proposed for this purpose. First we present the effect of desorption on the ZGB reactive to poisoned irreversible phase transition in the SR model. Next we discuss our recent research on KMC simulation of the SO model. The ZGB framework is utilized to propose a new model incorporating not only the standard Langmuir-Hinshelwood (LH) mechanism, but also introducing the Mars-van Krevelen (MvK) mechanism for the surface oxide phase [5]. Phase diagrams, which are plots between long time averages of various oscillating quantities against the normalized CO pressure, show two or three transitions depending on the CO coverage critical threshold (CT) value beyond which all adsorbed oxygen atoms are converted to surface oxide.

Spatial ordering of nano-dislocation loops in ion-irradiated materials

Defect microstructures formed in ion-irradiated metals, for example iron or tungsten, often exhibit patterns of spatially ordered nano-scale dislocation loops. We show that such ordered dislocation loop structures may form spontaneously as a result of Brownian motion of loops, biased by the angular-dependent elastic interaction between the loops. Patterns of spatially ordered loops form once the local density of loops produced by ion irradiation exceeds a critical threshold value.

Variability of fishing effort for the German brown shrimp (Crangon crangon) fishing fleet: influencing factors, and seasonal and spatial patterns

Abstract We examined factors affecting the fishing effort in the German brown shrimp (Crangon crangon) fishery, including shrimp and fuel price, catch per unit effort (cpue), number of days with strong wind, fishing port, and season. Time-series analysis (TS) using rational transfer functions (ARIMAX, an extension of autoregressive integrated moving average (ARIMA) modelling) were applied to model mean monthly boat effort (MBE, in hours), aggregated from the logbook data of five German ports for the years 2000–2008. We addressed two major areas: (i) whether cyclic effort patterns and the effect of external factors such as wind differ regionally, and (ii) whether external factors such as cpue, shrimp and fuel prices have a significant influence on the effort pattern. The estimated ARIMAX models accounted for 52–77% of the variance in MBE if analysed separately for each port, indicating a stable seasonal pattern of fishing effort without major interannual variations or significant trends. In spite of considerable variability in the external factors, none of cpue, shrimp or fuel price had a significant effect on the fishing effort. We interpreted this stability as a lack of alternative target species and discuss the theory that a response of a fishery to these external factors might only occur once certain critical threshold values have been exceeded, which was not the case during the investigated period. The models indicated differences in the seasonal patterns of the different harbours, with shorter trips and an earlier start for the main fishing season in the southwest (SW) regions, whereas in the northeast (NE) harbours, trips were longer, peak effort was shifted by 1–2 months and the spring season was of greater importance. The relationships of these regional patterns to the shrimp life cycle and coast topography, as well as implications for future management, are discussed.

Spatial and temporal variability of water quality in the coral reefs of Tayrona National Natural Park, Colombian Caribbean

Tayrona National Natural Park (TNNP) is a hotspot of coral reef biodiversity in the Colombian Caribbean, located between the city of Santa Marta (>455,000 inhabitants) and several smaller river mouths (Rio Piedras, Mendihuaca, Guachaca). The region also experiences a strong seasonal variation in physical parameters (temperature, salinity, wind, and water currents) due to alternating dry seasons with coastal upwelling and rainy seasons. However, the spatial and temporal effects on water quality parameters relevant for coral reef functioning have not been investigated. Therefore, inorganic nutrient, chlorophyll a, and particulate organic carbon (POC) concentrations along with biological O2 demand (BOD), pH, and water clarity directly above local coral reefs (~10 m water depth) were monitored for 25 months in four bays along a distance gradient (12-20 km) to Santa Marta in the southwest and to the first river mouth (17-27 km) in the east. This is by far the most comprehensive coral reefs water quality dataset for the region. Findings revealed that particularly during non-upwelling, chlorophyll a and POC concentrations along with BOD significantly increased with decreasing distance to the rivers in the east, suggesting that the observed spatial water quality decline was triggered by riverine runoff and not by the countercurrent-located Santa Marta. Nitrate, nitrite, and chlorophyll a concentrations significantly increased during upwelling, while pH and water clarity decreased. Generally, water quality in TNNP was close to oligotrophic conditions adequate for coral reef growth during non-upwelling, but exceeded critical threshold values during upwelling and in relation to riverine discharge.

Anisotropic radiation-induced segregation in 316L austenitic stainless steel with grain boundary character

Radiation-induced segregation (RIS) and subsequent depletion of chromium along grain boundaries has been shown to be an important factor in irradiation-assisted stress corrosion cracking in austenitic face-centered cubic (fcc)-based alloys used for nuclear energy systems. A full understanding of RIS requires examination of the effect of the grain boundary character on the segregation process. Understanding how specific grain boundary structures respond under irradiation would assist in developing or designing alloys that are more efficient at removing point defects, or reducing the overall rate of deleterious Cr segregation. This study shows that solute segregation is dependent not only on grain boundary misorientation, but also on the grain boundary plane, as highlighted by markedly different segregation behavior for the Σ3 incoherent and coherent grain boundaries. The link between RIS and atomistic modeling is also explored through molecular dynamic simulations of the interaction of vacancies at different grain boundary structures through defect energetics in a simple model system. A key insight from the coupled experimental RIS measurements and corresponding defect–grain boundary modeling is that grain boundary–vacancy formation energy may have a critical threshold value related to the major alloying elements’ solute segregation.

Sensitivity and evaluation of current fire risk and future projections due to climate change: the case study of Greece

Abstract. Current trends in the Mediterranean climate, and more specifically in Greece, indicate longer and more intense summer droughts that even extend out of season. In connection to this, the frequency of forest fire occurrence and intensity is on the rise. In the present study, the Canadian Fire Weather Index (FWI) is used in order to investigate the relationship between fire risk and meteorological conditions in Greece. FWI is a meteorologically based index designed in Canada and used worldwide, including the Mediterranean Basin, to estimate fire danger in a generalised fuel type based solely on weather observations. Here, an evaluation of the index is initially performed for the Greek territory using fire observations that cover a 15 yr period. Three critical fire risk threshold values are established for the area of Greece based on daily mean meteorological data: FWI = 15, FWI = 30 and FWI = 45, increasing from the northwest to the southeast. Subsequently, a regional climate model is employed providing input for the FWI system to investigate the impacts of climate change on fire risk for two future time periods, 2021–2050 and 2071–2100, under the A1B emissions scenario. Days with critical fire risk are expected to increase by as many as 50 days per year by the end of the century.

A New Method to Calculate Threshold Values of Ductile Fracture Criteria for Advanced High-Strength Sheet Blanking

A new approach is presented in this paper to calculate the critical threshold value of fracture initiation. It is based on the experimental data for forming limit curves and fracture forming limit curves. The deformation path for finally a fractured material point is assumed as two-stage proportional loading: biaxial loading from the beginning to the onset of incipient necking, followed plane strain deformation within the incipient neck until the final fracture. The fracture threshold value is determined by analytical integration and validated by numerical simulation. Four phenomenological models for ductile fracture are selected in this study, i.e., Brozzo, McClintock, Rice-Tracey, and Oyane models. The threshold value for each model is obtained through best-fitting of experimental data. The results are compared with each other and test data. These fracture criteria are implemented in ABAQUS/EXPLICIT through user subroutine VUMAT to simulate the blanking process of advanced high-strength steels. The simulated fracture surfaces are examined to determine the initiation of ductile fracture during the process, and compared with experimental results for DP780 sheet steel blanking. The comparisons between FE simulated results coupled with different fracture models and experimental one show good agreements on punching edge quality. The study demonstrates that the proposed approach to calculate threshold values of fracture models is efficient and reliable. The results also suggest that the McClintock and Oyane fracture models are more accurate than the Rice-Tracey or Brozzo models in predicting load-stroke curves. However, the predicted blanking edge quality does not have appreciable differences.

Diagnostic value of growth differentiation factor-15 and N-terminal pro-brain natriuretic peptide in children with congenital heart disease complicated with heart failure

Objective To assess the values of growth differentiation factor-15 (GDF-15) and N-terminal pro-brain natriuretic peptide (NT-proBNP) for the diagnosis of children with congenital heart disease(CHD) combined with heart failure. Methods Among the children under treatment at the First Affiliated Hospital of Xinjiang Medical University from Jan.2011 to Dec.2012, 206 children those suffered with CHD were selected as the case group.One hundred and five children without CHD or heart failure were selected as the control group.Improved Ross score≥3 grades was taken as reference standard for heart failure.The case group was divided into non-heart failure group (0-2 grades, 112 cases) and the heart failure group (3-12 grades, 94 cases). The heart failure group was divided into mild heart failure group (3-6 grades, 38 cases), moderate heart failure group (7-9 grades, 32 cases) and severe heart failure group (10-12 grades, 24 cases). Levels of plasma GDF-15 and NT-proBNP were tested.In the meanwhile, the left ventricular ejection fraction (LVEF) was tested with ultrasonic cardiogram.Linear correlation analysis was performed for evaluating levels of plasma GDF-15 and NT-proBNP against the cardiac function grading in Ross scores and the LVEF, respectively.ROC curve was made to determine critical point or threshold value of diagnosis and assess values of levels of plasma GDF-15 and NT-proBNP for diagnosis of congenital heart disease combined with heart failure. Results Comparison of age and gender differences between the case group and the control group showed no statistically significant(χ2=4.233, 4.360, P>0.05). Levels of plasma LogGDF-15 and LogNT-proBNP in the heart failure group were significantly higher than those values of the non-heart failure group and the control group(F=115.2, 63.2, all P<0.01). Levels of plasma GDF-15 and NT-proBNP increased with the severity of heart failure and were positively correlated with improved Ross scores (r=0.890, P<0.01) and negatively correlated with LVEF(r=-0.652, P<0.01). GDF-15 was considered in combination with NT-proBNP, the specificity(80.2%) and precision(77.9%) for diagnosis of heart failure could be enhanced when plasma GDF-15≥831.6 ng/L coexisted with NT-proBNP≥759.8 ng/L. Conclusions Plasma GDF-15 and NT-proBNP can help the diagnosis of heart failure caused by CHD in children.The increase of these two factors is closely related to the severity of clinical heart failure.Combination of these two factors for test can enhance specificity and precision for diagnosis of heart failure. Key words: Growth differentiation factor-15; N-terminal pro-brain natriuretic peptide; Congenital heart disease; Heart failure

Interpersonal Angular Relations between Players Constrain Decision-Making on the Passing Velocity in Futsal

The aim of this study was to investigate the influence of interpersonal interactions between players on the regulation of ball passing velocity in the team sport of futsal. For this purpose 28 sequences of play, in which passes were performed between outfield players, were selected from an elite futsal competition and analyzed using TACTO software. Relative angles between attackers and defenders were used to examine interpersonal coordination tendencies that emerged during performance. Results showed that ball passing velocity was constrained by the rate of change of the angle created by the following vectors: “ball carrier-ball receiver” and “ball carrier-ball receiver’s nearest defender”. Passing velocity remained the same when that angular value remained within a critical threshold range between ?18.16°/s to 11.26°/s. Beyond those critical threshold values, angular relations between participants seemed to enter into a new critical state requiring the emergence of a new passing velocity for performance success. The findings of this study allowed us to conclude that passing velocity during competitive performance in futsal was regulated by the rate of change of an angle established by the interaction between the ball carrier to ball receiver vector with the ball carrier to ball receiver’s nearest defender vector.

Why Don't Juries Try 'Range Voting'?

In this paper, the author proposes the use of a simple method by juries in which jurors would rate or score on a scale of zero to ten (or some other specified scale) the evidence presented by the parties at trial. The jury's verdict would thus consist of a numerical value, either the average or the sum total of all the individual scores, which the author refers to as a verdict. Range voting by juries thus produces a numerical verdict, a range verdict, consisting of an average value or total sum, and a plaintiff or other moving party would prove his case as a matter of law only if the average value or sum total of the jury's collective score exceeded some critical threshold value. In addition, the author explains how range voting solves several problems endemic to juries, including holdouts, strategic jurors, and ignorant or partially informed jurors. Lastly, the author also explains how range voting improves jury accuracy and examines the relation between his proposed model of range voting in juries and the diversity prediction theorem in mathematics or wisdom of crowds effect.

Long-range random-field Ising model: Phase transition threshold and equivalence of short and long ranges

The Ising model in a random field and with power-law decaying ferromagnetic bonds is studied at zero temperature. Comparing the scaling of the energy contributions of the ferromagnetic domain wall flip and of the random field a la Imry-Ma we obtain a threshold value for the power $\rho$ of the long-range interaction, beyond which no critical behavior occurs. The critical threshold value is $\rho_c=3/2$, at a difference with the zero field model in which $\rho_c=2$. This prediction is confirmed by numerical computation of the ground states below, at, and above this threshold value. Some possible implications for the critical behavior of spin-glasses in a field are conjectured.

On $${\alpha }$$ α -roughly weighted games

Gvozdeva et al. (Int J Game Theory, doi:10.1007/s00182-011-0308-4, 2013) have introduced three hierarchies for simple games in order to measure the distance of a given simple game to the class of (roughly) weighted voting games. Their third class \({\mathcal {C}}_\alpha \) consists of all simple games permitting a weighted representation such that each winning coalition has a weight of at least \(1\) and each losing coalition a weight of at most \(\alpha \). For a given game the minimal possible value of \(\alpha \) is called its critical threshold value. We continue the work on the critical threshold value, initiated by Gvozdeva et al., and contribute some new results on the possible values for a given number of voters as well as some general bounds for restricted subclasses of games. A strong relation between this concept and the cost of stability, i.e. the minimum amount of external payment to ensure stability in a coalitional game, is uncovered.

EVALUATION OF RAINFALL THRESHOLDS THROUGH ENTROPY: INFLUENCE OF BIVARIATE DISTRIBUTION SELECTION

ABSTRACTFloods cause severe damage worldwide in terms of human injury and have severe economic consequences, causing landslides, road accidents and inundation of agricultural areas. Non‐structural flood protection strategies offer the possibility to protect the land, preventing flood event effects. In particular, early warning systems can inform of flood occurrences. These systems can be based on the evaluation of a rainfall threshold value that is the rainfall amount that determines a critical discharge in a given river cross‐section. The alert is issued if the observed or forecast rainfall equals the threshold value without the support of online real‐time rainfall–runoff forecasting systems.The critical rainfall threshold values are evaluated by a probabilistic methodology, considering the joint cumulative distribution of cumulated rainfall and the corresponding peak discharge, for different durations. To estimate the joint distributions two approaches are considered: the meta‐Gaussian and the copula functions.The rainfall threshold values are estimated for the Mignone River basin (Italy). Results show that both joint distribution functions perform well in estimating the rainfall threshold values, as found from reliability analysis. In particular, the copula‐based approach leads to issuing the alert in advance. Copyright © 2013 John Wiley &amp; Sons, Ltd.

Ecology of the ciguatera causing dinoflagellates from the Northern Great Barrier Reef: Changes in community distribution and coastal eutrophication

Ciguatera fish poisoning (CFP) is known to be caused by the ciguatoxins from the dinoflagellate genus Gambierdiscus, however, there is the potential for other toxins such as okadaic acid and dinophysistoxins from the genus Prorocentrum, and palytoxin from the genus Ostreopsis, to contaminate seafood. These genera may also be indicators of ecosystem health and potentially impact on coral reef ecosystems and the role they may play in the succession of coral to macroalgae dominated reefs has not been researched. Sixteen GBR field sites spanning inshore, mid-lagoon and outer lagoon (offshore) regions were studied. Samples were collected from September 2006 to December 2007 and abundance of benthic dinoflagellates on different host macroalgae and concentration of nutrients present in the water column were determined. The maximum abundance of Prorocentrum, Ostreopsis and Gambierdiscus found was 112, 793 and 50 cells per gram wet weight of host macroalgae, respectively. The average level of Dissolved Inorganic Nitrogen (DIN) in the water column across all sites (0.03mg/L) was found to be more than double the threshold critical value (0.013mg/L) for healthy coral reefs. Compared to a previous study 1984, there is evidence of a major shift in the distribution and abundance of these dinoflagellates. Inshore reefs have either of Prorocentrum (as at Green Island) or Ostreopsis (as at Magnetic Island) dominating the macroalgal surface niche which was once dominated by Gambierdiscus, whilst at offshore regions Gambierdiscus is still dominant. This succession may be linked to the ongoing eutrophication of the GBR lagoon and have consequences for the sources of toxins for ongoing cases of ciguatera.