Relation between responses in the neutral red retention test and the comet assay and life history parameters of Daphnia magna.

Responses of the neutral red retention (NRR) assay as test for lysosomal stability and the comet assay as test for DNA integrity were measured in the water flea, Daphnia magna, and compared with mortality and effects on population growth rate during short- or long-term exposure to seven different toxicants. The NRR test and the comet assay were performed with fresh preparations of pieces of tissue from the digestive tract or with cell preparations from whole daphnias. Five toxicants caused responses of the NRR test or the comet assay after short-term exposure at concentrations below the acute toxicity level. Preliminary results of long-term exposure experiments suggest that these biomarker responses can be related to chronic effects on survival and/or reproduction of D. magna. This type of research should provide the basis for future use of the NRR test and the comet assay as early warning biomarkers for effects of toxicants on Daphnia populations.     

The requirements for stable metallothionein clusters examined using synthetic lobster domains.

Metallothioneins (MTs) are small, cysteine-rich proteins which detoxify xenobiotic metals such as cadmium (Cd) and mercury (Hg). In crustaceans and mammals they consist of two independent domains which are folded around metal-thiolate clusters. MT clusters of different origins, exhibiting distinct, highly conserved cysteine positions on their sequences, show differences in metal-cysteine coordination and reactivity. Lobster-MT, containing two Cd3 beta domains, is an important model for structure-function relationships among the clusters. The influence of (1) the position of the cysteine residues and (2) steric and electrostatic effects of neighboring amino acids on the folding and stability of MT cluster were investigated. Thus, the native lobster beta C and beta N domains (each having nine cysteines and binding three M2+ ions) and a modified domain Cd3 beta C-->N, in which the cysteines of the C-terminal domain were relocated to match the positions of those in the N-terminal domain, were chemically prepared and characterized. The synthetic native domains (Cd3 beta C and Cd3 beta N) were found to exhibit spectroscopic properties, metal-binding affinities and kinetic reactivity similar to the holo-protein. However, the modified Cd3 beta C-->N domain was unusually reactive and in the presence of Chelex, metal chelation resin, aggregated to a Cd5(beta C-->N)2 dimer, which exhibited unusual structure as observed by its 113Cd-nuclear magnetic resonance. These differences in structure and reactivity demonstrated that the requirements for formation of a stable Cd3S9 beta-cluster are more stringent than simply the sequential positions of the cysteines along the peptide chain and must include interactions involving neighboring, noncysteine amino acids.     

Stable carbon isotope distribution of particulate organic matter in the ocean: a model study

The stable carbon isotopic composition of particulate organic matter in the ocean, δ¹³C_POC, shows characteristic spatial variations with high values in low latitudes and low values in high latitudes. The lowest δ¹³C_POC values (−32‰ to −35‰) have been reported in the Southern Ocean, whereas in arctic and subarctic regions δ¹³C_POC values do not drop below −27‰. This interhemispheric asymmetry is still unexplained. Global gradients in δ¹³C_POC are much greater than in δ¹³C_DIC, suggesting that variations in isotopic fractionation during organic matter production are primarily responsible for the observed range in δ¹³C_POC. Understanding the factors that control isotope variability is a prerequisite when applying δ¹³C_POC to the study of marine carbon biogeochemistry. The present model study attempts to reproduce the δ¹³C_POC distribution pattern in the ocean. The three-dimensional (3D) Hamburg Model of the Oceanic Carbon Cycle version 3.1 (HAMOCC3.1) was combined with two different parametrizations of the biological fractionation of stable carbon isotopes. In the first parametrization, it is assumed that the isotopic fractionation between CO₂ in seawater and the organic material produced by algae, _P, is a function of the ambient CO₂ concentration. The two parameters of this function are derived from observations and are not based on an assumption of any specific mechanism. Thus, this parametrization is purely empirical. The second parametrization is based on fractionation models for microalgae. It is supported by several laboratory experiments. Here the fractionation, _P, depends on the CO₂ concentration in seawater and on the (instantaneous) growth rates, μ_i, of the phytoplankton. In the Atlantic Ocean, where most field data are available, both parametrizations reproduce the latitudinal variability of the mean δ¹³C_POC distribution. The interhemispheric asymmetry of δ¹³C_POC can mostly be attributed to the interhemispheric asymmetry of CO₂ concentration in the water. However, the strong seasonal variations of δ¹³C_POC as reported by several authors, can only be explained by a growth rate-dependent fractionation, which reflects variations in the cellular carbon demand.     

Nitrogen uptake and primary productivity rates in the Mid-Atlantic Bight (MAB)

Nutrient concentrations, primary productivity, and nitrogen uptake rates were measured in coastal waters of the Mid-Atlantic Bight over a two-year period that included measurements from all four seasons. In order to assess carbon productivity and nitrogen demand within the context of the physical environment, the region was divided into three distinct hydrographic regimes: the Chesapeake and Delaware Bay outflow plumes (PL), the southern Mid-Atlantic shelf influenced by the Gulf Stream (SS), and the mid-shelf area to the north of the Chesapeake Bay mouth (MS). Annual areal rates of total nitrogen (N) uptake were similar across all regions (10.9 ± 2.1 mol N m⁻² y⁻¹). However, annual areal rates of net primary productivity were higher in the outflow plume region (43 mol C m⁻² y⁻¹), than along the Mid-Atlantic shelf and in areas influenced by the Gulf Stream (41 and 34 mol C m⁻² y⁻¹, respectively). Rates of net primary productivity were not well correlated with Chl a concentrations and were uncoupled with net N uptake rates. Seasonally averaged annual areal rates of net primary productivity for the Mid-Atlantic Bight measured in this study were higher than those calculated in previous decades and provide important validation information for biogeochemical models and satellite remote sensing algorithms developed for the region.     

Incentives,social–ecological feedbacks and European fisheries

The European Common Fisheries Policy (CFP) has failed to deliver on social, economic and ecological goals. This failure is in part the result of a number of social–ecological feedback mechanisms. The policy is currently undergoing reform, with unknown practical outcomes. Here, relatively successful fisheries policies outside the European Union are reviewed. Through interviews and workshops with scientists, managers and other stakeholders, complemented with literature reviews, practices that can create incentives for long-term sustainability are investigated. The focus is on how the provision of clear and trusted scientific evidence can stimulate defensible decisions, in turn creating incentives for compliance, leading to positive social–ecological outcomes. Despite differences between Europe and the investigated case studies, the prospects of an increased regionalization within the European CFP provides the best starting point for implementing best practice identified in this study.     

Study of the motions of fishing vessels by a time domain panel method

In this paper, a wide variety of computed motion results is presented for three existing fishing vessels. In order to do that, time domain computations of 3D ship motions are performed with a time domain Green's function. The computational method adopted is based on a previously developed one, whose numerical scheme here is subjected to modifications that increase its robustness and overall efficiency, so that it can be applied to calculate the motions of fishing vessels. The results are then compared with simulations using WAMIT for the zero speed case, and a strip theory method is used to determine the effect of forward speed. Results are presented for head seas, quartering head waves and following waves with three distinct Froude numbers.     

Design and testing of a non-linear power take-off simulator for a bottom-hinged plate wave energy converter

Eddy current brakes provide a versatile way of simulating the power take-off system (PTO) in model testing of small scale wave energy converters (WECs). This type of PTO simulator is based on the principle that a conductive material moving in a magnetic field generates a braking force proportional to its velocity. A bottom-hinged pitching plate WEC model has been designed using an eddy current brake as a PTO simulator. A dedicated electric current source unit was developed to provide a controllable and reliable level of DC current intensity to feed the magnetic field generating coils. Using a real-time data acquisition and control, this unit can be used to impose non-linear damping PTO characteristic curves in several types of WEC models based on eddy current brakes. In the present case, this current source has been used to simulate a constant damping PTO on a small scale pitching WEC model that has been tested in the IST wave flume. Two different cases were considered: one corresponding to a surface piercing plate and another to a fully submerged plate. Experimental results are presented for plate motion and for non-dimensional capture width.