Gert Van Hoey

A bioturbation classification of European marine infaunal invertebrates

Bioturbation, the biogenic modification of sediments through particle reworking and burrow ventilation, is a key mediator of many important geochemical processes in marine systems. In situ quantification of bioturbation can be achieved in a myriad of ways, requiring expert knowledge, technology, and resources not always available, and not feasible in some settings. Where dedicated research programmes do not exist, a practical alternative is the adoption of a trait-based approach to estimate community bioturbation potential (BPc). This index can be calculated from inventories of species, abundance and biomass data (routinely available for many systems), and a functional classification of organism traits associated with sediment mixing (less available). Presently, however, there is no agreed standard categorization for the reworking mode and mobility of benthic species. Based on information from the literature and expert opinion, we provide a functional classification for 1033 benthic invertebrate species from the northwest European continental shelf, as a tool to enable the standardized calculation of BPc in the region. Future uses of this classification table will increase the comparability and utility of large-scale assessments of ecosystem processes and functioning influenced by bioturbation (e.g., to support legislation). The key strengths, assumptions, and limitations of BPc as a metric are critically reviewed, offering guidelines for its calculation and application.

The Validation of the Finite Difference Method and Reciprocity for Solving the Inverse Problem in EEG Dipole Source Analysis

The performance of the finite difference reciprocity method (FDRM) to solve the inverse problem in EEG dipole source analysis is investigated in the analytically solvable three-shell spherical head model for a large set of test dipoles. The location error for a grid with 2 mm and 3 mm node spacing is in general, not larger than twice the internode distance, hence 4 mm and 6 mm, respectively. Increasing the number of scalp electrodes from 27 to 44 only marginally improves the location error. The orientation error is always smaller than 4° for all the test dipoles considered. We have also compared the sensitivity to noise using FDRM in EEG dipole source analysis with the sensitivity to noise using the analytical expression for the forward problem. FDRM is not more sensitive to noise than the method using the analytical expression.

Influence of hypovolemia on the pharmacokinetics and the electroencephalographic effect of propofol in the rat.

BackgroundHypovolemia decreases the dose requirement for anesthetics, but no data are available for propofol. As it is impossible to study this in patients, a rat model was used in which the influence of hypovolemia on the pharmacokinetics and pharmacodynamics of propofol was investigated. MethodsAnimals were randomly allocated to either a control (n = 9) or a hypovolemia (n = 9) group, and propofol was infused (150 mg · kg−1 · h−1) until isoelectric periods of 5 s or longer were observed in the electroencephalogram. The changes observed in the electroencephalogram were quantified using aperiodic analysis and used as a surrogate measure of hypnosis. The righting reflex served as a clinical measure of hypnosis. ResultsThe propofol dose needed to reach the electroencephalographic end point in the hypovolemic rats was reduced by 60% (P < 0.01). This could be attributed to a decrease in propofol clearance and in distribution volume. Protein binding was similar in both groups. To investigate changes in end organ sensitivity during hypovolemia, the electroencephalographic effect versus effect–site concentration relation was studied. The effect–blood concentration relation was biphasic, exhibiting profound hysteresis in both hypovolemic and control animals. Semiparametric minimization of this hysteresis revealed similar equilibration half-lives in both groups. The biphasic effect–concentration relation was characterized by descriptors showing an increased potency of propofol during hemorrhage. The effect–site concentration at the return of righting reflex was 23% (P < 0.01) lower in the hypovolemic animals, also suggesting an increased end organ sensitivity. ConclusionsAn increased hypnotic effect of propofol occurs during hypovolemia in the rat and can be attributed to changes in both pharmacokinetics and end organ sensitivity.

On the Myths of Indicator Species : Issues and Further Consideration in the Use of Static Concepts for Ecological Applications

The use of static indicator species, in which species are expected to have a similar sensitivity or tolerance to either natural or human-induced stressors, does not account for possible shifts in tolerance along natural environmental gradients and between biogeographic regions. Their indicative value may therefore be considered at least questionable. In this paper we demonstrate how species responses (i.e. abundance) to changes in sediment grain size and organic matter (OM) alter along a salinity gradient and conclude with a plea for prudency when interpreting static indicator-based quality indices. Six model species (three polychaetes, one amphipod and two bivalves) from the North Sea, Baltic Sea and the Mediterranean Sea region were selected. Our study demonstrated that there were no generic relationships between environment and biota and half of the studied species showed different responses in different seas. Consequently, the following points have to be carefully considered when applying static indicator-based quality indices: (1) species tolerances and preferences may change along environmental gradients and between different biogeographic regions, (2) as environment modifies species autecology, there is a need to adjust indicator species lists along major environmental gradients and (3) there is a risk of including sibling or cryptic species in calculating the index value of a species.

Comparison of performance of spherical and realistic head models in dipole localization from noisy EEG

The performance of a three-shell spherical head model versus the performance of a realistic head model is investigated when solving the inverse problem with a single dipole, in the presence of noise. This is evaluated by calculating the average dipole location error for 1000 noisy scalp potential sets, originating from the same test dipole and having the same noise level. The average location errors are obtained utilizing a local linearization, which is validated with a Monte-Carlo simulation. When the difference between the average location error utilizing a spherical and a realistic head model, represented by deltaR, is large for a large number of test dipoles, then it is worth using the more computationally demanding realistic head model. However, if deltaR is small for a large number of test dipoles, then it does not matter which model is used. For 27 electrodes, an electroencephalogram (EEG) epoch of one time sample and spatially white Gaussian noise, we found that the importance of the realistic head model over the spherical head model reduces by increasing the noise level. We further found that increasing the number of scalp electrodes from 27 to 44 has limited impact on the importance of the realistic head model over the spherical head model in EEG dipole source analysis. By increasing the number of time samples to six, the performance of the realistic head model in the inverse calculation gains importance compared with the three-shell spherical head model. Finally, we used spatially and temporally correlated background EEG instead of Gaussian noise. The advantage of the realistic head model over the spherical head model is reduced when applying correlated noise compared to Gaussian noise.

EEG dipole source localization using artificial neural networks

Localization of focal electrical activity in the brain using dipole source analysis of the electroencephalogram (EEG), is usually performed by iteratively determining the location and orientation of the dipole source, until optimal correspondence is reached between the dipole source and the measured potential distribution on the head. In this paper, we investigate the use of feed-forward layered artificial neural networks (ANNs) to replace the iterative localization procedure, in order to decrease the calculation time. The localization accuracy of the ANN approach is studied within spherical and realistic head models. Additionally, we investigate the robustness of both the iterative and the ANN approach by observing the influence on the localization error of both noise in the scalp potentials and scalp electrode mislocalizations. Finally, after choosing the ANN structure and size that provides a good trade off between low localization errors and short computation times, we compare the calculation times involved with both the iterative and ANN methods. An average localization error of about 3.5 mm is obtained for both spherical and realistic head models. Moreover, the ANN localization approach appears to be robust to noise and electrode mislocations. In comparison with the iterative localization, the ANN provides a major speed-up of dipole source localization. We conclude that an artificial neural network is a very suitable alternative for iterative dipole source localization in applications where large numbers of dipole localizations have to be performed, provided that an increase of the localization errors by a few millimetres is acceptable.

Relationship Between Etomidate Plasma Concentration and EEG Effect in the Rat

AbstractPurpose. The effect-plasma concentration relationship of etomidate was studied in the rat using electroencephalographic changes as a pharmacodynamic parameter. Methods. Etomidate was infused (50 mg/kg/h) in chronically instrumented rats (n = 6) until isoelectric periods of 5 s or longer were observed in the electroencephalogram (EEG). The EEG was continuously recorded during the experiment and frequent arterial blood samples were taken for determination of etomidate plasma concentrations. The changes observed in the raw EEG signal were quantified using aperiodic analysis in the 2.5−7.5 Hz frequency band. The return of the righting reflex was used as another parameter of anesthesia. Results. A mean dose of 8.58 ± 0.41 mg/kg needed to be infused to reach the end point of 5 s isoelectric EEG. The plasma concentration time profiles were most adequately fitted using a three-exponential model. Systemic clearance, volume of distribution at steady-state and elimination half-life averaged 93 ± 6 ml/min/kg, 4.03 ± 0.24 l/kg and 59.4 ± 10.7 min respectively. The EEG effect-plasma concentration relationship was biphasic exhibiting profound hysteresis. Semi-parametric minimization of this hysteresis revealed an equilibration half-life of 2.65 ± 0.15 min, and the biphasic effect-concentration relationship was characterized nonparametrically by descriptors. The effect-site concentration at the return of the righting reflex was 0.44 ± 0.03 μg/ml. Conclusions. The results of the present study show that the concentration-effect relationship of etomidate can be characterized in individual rats using aperiodic analysis in the 2.5−7.5 Hz frequency band of the EEG. This characterization can be very useful for studying the influence of diseases on the pharmacodynamics of etomidate in vivo.

Similar diversity-disturbance responses to different physical impacts: Three cases of small-scale biodiversity increase in the Belgian part of the North Sea

Human activities at sea are still increasing. As biodiversity is a central topic in the management of our seas, it is important to understand how diversity responds to different disturbances related with physical impacts. We investigated the effects of three impacts, i.e. sand extraction, dredge disposal and offshore wind energy exploitation, on the soft-bottom macrobenthic assemblages in the Belgian part of the North Sea. We found similar diversity-disturbance responses, mainly related to the fact that different impacts caused similar environmental changes. We observed a sediment refinement which triggered a shift towards a heterogenic, dynamic (transitional) soft-bottom macrobenthic assemblage, with several species typically associated with muddy sands. This led to a local unexpected biodiversity increase in the impacted area. On a wider regional scale, the ever increasing human impacts might lead to a homogenization of the sediment, resulting in a more uniform, yet less diverse benthic ecosystem.

Assessing the impact degree and areal degradation extent of the benthic ecosystem caused by different human activities.

How sustainable are human activities and at what pace do they impact the ecosystem? An ongoing debate urging for uniform assessments. The EU Nature Directives (Marine Strategy Framework, Habitat and Water Framework Directives) provide good bases for scientifically sound assessments. However, they all have different assessment criteria, hampering the objective comparison of the impact degree and the areal extent of degradation caused by human activities. In this study, we applied a harmonized and uniform set of biodiversity indicators, as defined for MSFD-Descriptor 1 with respect to the benthic ecosystem in the Belgian North Sea. We assessed the impact of dredge disposal and aggregate extraction, two activities only allowed in dedicated zones, and compared this to the impact of the more widespread fishery activity. At certain pressure thresholds (e.g. volume disposed, volume and frequency of extraction, number of trawls), all activities caused a decrease in benthic habitat quality. However, for each activity the thresholds and the areal extent of degradation were quite different dependent on the benthic habitat type in which the activity took place. Such detailed insights on pressure footprints are necessary, to allow for an integrated evaluation of the biodiversity status across multiple activities within different marine regions.

Long-term trends in soft-bottom fauna based on 30 years biodiversity monitoring systems

From 1984 onwards, several locations (outside direct human impact) were yearly sampled for macrobenthos, epibenthos and demersal fish in autumn. This provided a unique dataset to study natural variability over time within the soft-bottom ecosystem. Both coastal and offshore assemblages of each ecosystem component were sampled, which permitted to detect if the coastal and offshore area changed differently over time within one ecosystem component. Furthermore, these long-term data enabled to identify whether the different ecosystem components showed similar or different trends over time. Observed changes were linked to physical and climate-related environmental variables.