ALBERT

Description: Predation pressure was examined for the epibenthic fauna of a intertidal seagrass bed of the Sylt-Rømø bight. Starting from the question for the dominant epibenthic prey and the intensity of predation pressure in seagrass habitats, we investigated a seegrasbed in the Sylt- Rømø bight. in sommer 2003. A predator enclosure experiment has been carried out in artificial tide pools of similar size, and a bait experiment were carried out in the surrounding seagrass bed. The most frequent epibenthic organisms within the intertidal seagrass beds consist of four dominant species: The brown shirmp (Crangon crangon, Linnaeus), the sand goby (Pomatoschitus microps, Krøyer), the isopode (Idotea balthica, Pallas) and the shore crab (Carcinus maenas, Linnaeus.). C. crangon showed an average annual abundance during high water of approximately 80 animals per m-2 (P.POL TE pers. Com.). Pomatoschistus microps and Carcinus maenas showed an average annual abundance of 7 animals m 2 and of 195 animals m-2. An abundance of 26 individuals m-2 was found for I. balthica (P.POLTE pers. Com.). As shown for the seagrass bed, C.crangon, P.microps and C.maenas were also the dominant forms in the tide pools. I. balthica could be found with 26 individuals m-2. The abundance of C. crangon were measured with an Annual average of 157 animals m-2 and therefore showed different results for the seagrassbeds. P. microps and C. maenas showed an average annual abundance of 15 animals m-2 and of 22 animals m-2 respectively. Mobile fauna migrates with the ebb tide into deeper waters (e.g. Pomatoschistus microps.) The substantially lower results of C. maenas within tide pools compared to adjacent seagrass beds can be partly explained by sampling time. In the seagrasbed sampling started earlier in the year (of May), and included the larval and juvenile stages of C. maenas. This led to a substantially higher abundance. Low abundance of I. balthica can be explained by its requirement for a structured habitat. I. balthica needs branched algal structures as a firm substrat. Such structures were hardly available in the tide pools...

Description: In Europe, increased attempts to intensify crayfish aquaculture have been carried out in recent years. Some of the major problems arising from the intensification are related to dietary supply of the animals in culture ponds and tanks. This study therefore focussed on some of the key objectives supporting the development of suitable diets for signal crayfish Pacifastacus leniusculus aquaculture. A large-scale response surface experiment was carried out to study the influences of different macronutrients (protein, lipid, carbohydrate) on crayfish growth and body composition. The results from this experiment led to the development of an improved experimental diet containing high levels of protein and carbohydrates, while increased lipid concentrations seemed to be influencing growth adversely. Further experiments were carried out to improve diet quality. For this purpose, diet types and the suitability of different binding agents were investigated. A small experiment was carried out to monitor the effects of attractants on growth of juvenile signal crayfish. A second objective of this study was the establishment of a new method to measure physiological responses of crayfish to different treatments. Running mid-term or long term experiments require high amounts of resources and slow down the process of dietary development. The measurement of RNA/DNA ratio has proven to be a suitable instrument to examine short-term metabolic responses to different key factors such as feeding regime, diet quality and digestibility and bioavailability of essential nutrients. The study has stressed the importance of proper diet preparation and composition for successful astaciculture. Binding agents were found to have major influence on diet digestibility and bioavailability of macronutrients. As another result of this study, further experiments are regarded to be necessary to examine the response of signal crayfish to different levels of lipid and protein in their diet. Some of the results obtained suggest a lack of regulatory capacity regarding the animals’ protein/lipid ratio. Further experiments however will have to be carried out to proof this hypothesis.

Description: In this study the mean tropospherical total zonal energy fluxes based on the NCEPNCAR reanalyses data are calculated for the time period 1948-2003. The interannual wintertime variability and the vertical structure of the fluxes are analysed. Since the dominant mode of atmospheric variability, the North Atlantic Oscillation, modulates the mean zonal current over the northern Atlantic region on monthly timescales, the NAO is expected to be the main cause for the interannual variability of energy fluxes. This study aims to analyse the linkage between this variabilty of zonal energy fluxes and the NAO. If the interannual variability of zonal energy transport directed to the european continent is associated with the NAO, the interannual energy flux variability can be referred to the variability of atmospheric circulation. In the first section, a climatology shows the three-dimensional structure of the mean zonal energy fluxes and its interannual seasonal standard deviations. In the second section, the dominant patterns of variability in various cross-sections parallel to the circles of longitude are obtained by EOF-analysis. The two leading EOF-patterns show barotropic structures, which in general agree in all sections. The 1.EOF explains more than 50% of the variance, the 2.EOF 25%. There exists however a significant correlation between the principle components only of the first EOFs of the western and eastern cross sections. The connection between zonal fl ux anomalies and the NAO yields a di polar correlationstructure, which is comparable to the correlation-pattern between the NAO and the zonal wind. The barotropic feature is predominant in each cross-section, moreover the regression-patterns show an eastward increasing tilt of the vertical axis towards north with a clear downward propagation of the northern center of activity from the middle troposphere to the lowest levels over Europe. It is shown that the NAO explains more than 30% of the total variance of interannual variability of the seasonal zonal energy fluxes, over the central Atlantic region even more than 40%, whereby anomalies reach up to 30% of the seasonal mean fluxes during extreme NAO-phases. Subsequently, flux anomalies associated with the Niño3-SST are analysed to clarify the dependence upon ENSO. In western parts of the Atlantic region, the Niño3-SST explains less than 5% of the variability of the zonal energy fluxes. Correlations between them are widely non significant in the analysed area. Nevertheless, strong El Niño events tend to cause stronger flux anomalies. In the last section, vertically integrated energy fluxes through the western and eastern boundary of the Atlantic region (represented as 60°W and 0°W longitudes) are computed. Fluctuations of the total energy flux through these sections are proved to be highly correlated with the NAO. The zonal convergence of flux anomalies between the boundaries show weak linkages to NAO, so that meridional atmospheric energy transport anomalies associated with NAO in the Atlantic region are assumed.

Description: The aim of this study is to examine the influence of both thermohaline and wind driven circulation changes on oceanic and atmospheric CO2-concentrations. For this the biopump three- and seven-box models of Toggweiler [1999] are integrated from an interglacial into a glacial steady state and vice versa. In contrast to previous studies which concentrated on steady state situations, here the focus is on transient CO2-concentrations after a sudden change in thermohaline and wind driven circulations. In addition timescales and amplitudes of atmospheric pC02-concentrations during the transition are compared to measurements of ice core datasets.

Description: Studies of animal populations are important and, in the case of harbour seals, have been considered particularly valuable as part of an assessment of the distemper epidemic that has plagued the northern Atlantic population over the last years. Head counts of seals by plane- or ship-based observers are biassed because these animals spent a large percentage of their time underwater. This study seeks to quantify the time that seals can be seen so that head counts can be appropriately corrected. Over the last two years 19 harbour seals were equipped with multiple channel loggers which recorded dive depth every 3-15 seconds for periods lasting up to two month. In this work the diving behaviour of 11 seals, from which the devices could be recovered, was analysed to examine how much time the animals spent at the water surface and on land where they can be counted and the extent to which this varied according to behaviour and water depth. Dives executed conformed broadly to either U- or V-shaped dives according to their profile of depth over time. During U-shaped dives, which comprised about 80% of all dives, the seals always apparently dived to the seabed. Both dive duration and surface duration changed systematically with maximum depth reached during the dive, both increasing: surface time as a cubed function of water depth and dive duration as a squared function of water depth. The percentage time that seals spent at the water surface where they can be seen could described by the equation: % time at surface = (21,55+0,00016( depth)3) / (21,55+0,00016(depth)3)+(156, 7+6,07(1n(depth)2) X 100 Implementation of this formula on seal-counting transects should help in calculations of seal density at sea and thus be useful in population assessments.

Description: Hydrogen peroxide (H2O2) is cytotoxic and as a reactive oxygen species (ROS) elicits oxidative stress in marine organisms (Viarengo et al. 1998). There are several sources of (H2O2) to the surface layers of the oceans and Antarctic diatoms do have the ability to decompose H202 in seawater. They decompose certain amounts of H202 in the dark and in the light and bacteria have a minor effect on the decomposition. All species of marine diatoms tested (F. cylindrus, F kerguelensis, C. dichaeta, C. debilis, and Actinocyclus sp.) were able to decompose H202 at first order. The rate constants (k) for these species of phytoplankton ranged between ~-2.0 - -5.0*10-03 μg chl-a-1 l-1 h-1. Actinocyclus sp. was the most efficient, while C. dichaeta was the least efficient decomposer. The decomposition is mediated through catalase and peroxidase enzymes inside the cell and efficiency is dependent on the permeability of the cell wall for H202 of one cell. One marine diatom (C. debilis) used in the experiments was a producer of H202 in the dark but at negligible concentrations regarding other sources of H202 like photoproduction or precipitation to the oceans.

Description: Obwohl im terrestrischen Bereich die induzierte Verteidigung durch Herbivore weit verbreitet ist, sind nur wenige Beispiele für marine Makrophyten bekannt. In dieser Studie wurden in zwei Laborexperimenten die Effekte von 1. direktem Fraß durch Amphipoden und 2. wassergetragenen Signalen von Fraß an benachbarten Algen und 3. der Effekt eines benachbarten Konsumenten auf die Antifraßverteidigung von sieben bzw. vier Makroalgen der portugiesischen Südküste untersucht. Die Braunalge Fucus vesiculosus und die Rotalge Sphaerococcus coronopifolius wiesen nach einer Behandlungsphase von 14 Tagen mit drei Amphipodenarten als Konsumenten eine induzierte Verteidigung in intakten Algenstücken auf. Diese Verteidigung wurde innerhalb von zwei Wochen wieder herabgesetzt, nachdem der Fraßdruck reduziert wurde. Für F. vesicu/osus konnte weiter nachgewiesen werden, dass die Verteidigung teilweise auf den lipophilen Bestandteilen der Pflanze beruht. Außerdem konnte für beide Algenarten eine saisonale Variation in der Intensität des Auftretens der Verteidigungsinduktion beobachtet werden. Weiterhin konnte festgestellt werden, dass wassergetragene Signale von 1. benachbartem Fraß sowie 2. von einem benachbarten Konsumenten, der nicht fraß, eine Antifraßverteidigung auslösen. Diese Studie zeigt, dass nicht nur Braunalgen dazu in der Lage sind, auf die Signale von Herbivoren in kürzester Zeit - also innerhalb von 14 Tagen - zu reagieren, sondern dass dies auch bei Rotalgen der Fall sein kann. Nach unserem Wissen ist dies die erste Studie, die zeigt, dass bei Rotalgen eine Verteidigung durch direkten Fraß induziert werden kann und dass wassergetragene Signale von einem nicht fressenden Konsumenten ebenfalls eine Verteidigung auslösen. Hieran ist zu erkennen, dass induzierte Verteidigung durch direkten Fraß wie auch durch wassergetragene Signale in marinen Makrophyten eine größere ökologische Relevanz spielt, als bisher angenommen wurde.

Description: Volcanogenic massive sulfide deposits may represent a significant future source of Te, which is a critical element important for the green energy transition. Tellurium is enriched in these settings by up to 10,000 times over its crustal abundance, indicating that fluids in sea-floor hydrothermal systems may transport and precipitate Te. The major element composition of these hydrothermal fluids is controlled by fluid-rock interaction and is well documented based on experimental, modeling, and natural studies; however, controls on Te mobility are still unknown. To better understand Te enrichment in this deposit type, numerical simulations of the mafic-hosted Vienna Woods and the felsic-hosted Fenway sea-floor vents in the Manus basin were performed to predict Te mobility in modern sea-floor hydrothermal vent fluids and Te deposition during sulfide formation. These simulations demonstrate that the mobility of Te in sea-floor hydrothermal systems is primarily controlled by fluid redox and temperature. Tellurium mobility is low in reduced hydrothermal fluids, whereas mobility of this metal is high at oxidized conditions at temperatures above 250°C. Numerical simulations of the reduced vent fluids of the mafic-hosted Vienna Woods site at the back-arc spreading center in the Manus basin yielded Te concentrations as low as 0.2 ppt. In contrast, the more oxidized model fluids of the felsic-hosted Fenway site located on Pual Ridge in the eastern Manus basin contain 50 ppt Te. The models suggest that Te enrichment in these systems reflects rock-buffer control on oxygen fugacity, rather than an enriched source of Te. In fact, the mafic volcanic rocks probably contain more Te than felsic volcanic rocks. The association of elevated Te contents in the felsic-hosted Fenway system likely reflects magmatic volatile input resulting in lower pH and higher Eh of the fluids. More generally, analysis of sulfide samples collected from modern sea-floor vent sites confirms that redox buffering by the host rocks is a first-order control on Te mobility in hydrothermal fluids. The Te content of sulfides from sea-floor hydrothermal vents hosted by basalt-dominated host rocks is generally lower than those of sulfides from vents located in felsic volcanic successions. Literature review suggests that this relationship also holds true for volcanogenic massive sulfides hosted in ancient volcanic successions. Results from reactive transport simulations further suggest that Te deposition during sulfide formation is primarily temperature controlled. Modeling shows that tellurium minerals are coprecipitated with other sulfides at high temperatures (275°–350°C), whereas Te deposition is distinctly lower at intermediate (150°–275°C) and low temperatures (100°–150°C). These predictions agree with geochemical analyses of sea-floor sulfides as Te broadly correlates positively with Cu and Au enrichment in felsic-hosted systems. The findings of this study provide an important baseline for future studies on the behavior of Te in hydrothermal systems and the processes controlling enrichment of this critical mineral in polymetallic sulfide ores.