ALBERT

Description: This paper describes a Bayesian inversion of acoustic reflection loss versus angle measurements to estimate the compressional and shear wave velocities in young uppermost oceanic crust, Layer 2A. The data were obtained in an experiment on the thinly sedimented western flank of the Endeavor segment of the Juan de Fuca Ridge, using a towed horizontal hydrophone array and small explosive charges as sound sources. Measurements were made at three sites at increasing distance from the ridge spreading center to determine the effect of age of the crust on seismic velocities. The inversion used reflection loss data in a 1/3-octave band centered at 16 Hz. The compressional and shear wave velocities of the basalt were highly sensitive parameters in the inversion. The compressional wave velocity increased from 2547±30 to 2710±18 m/s over an age span of 1.4 million years (Ma) from the spreading center, an increase of 4.5±1.0%/Ma. The basalt shear wave velocity increased by nearly a factor of 2, from ∼725 to 1320 m/s over the same age span. These results show a decreasing trend of Poisson’s ratio with age, from a value of 0.46 at the youngest site closest to the ridge axis.

Description: This first “World Ocean Review” is published in 2010 and will be followed by periodic updates in the future. The result is a comprehensive, detailed and unique report about the state of the world’s oceans and their interplay with ecological, economic and sociopolitical conditions. Its aim is to increase public awareness of the interconnected nature of the diverse aspects of the marine environment and thus to boost marine conservation.

Description: Der „World Ocean Review" erscheint 2010 das erste Mal und soll in Zukunft in regelmäßigen Abständen herausgegeben werden. Entstanden ist ein umfassender und profunder Bericht, der den Zustand der Weltmeere und die Wirkungszusammenhänge zwischen dem Ozean und ökologischen, ökonomischen und gesellschaftspolitischen Bedingungen aufzeigt. Die wissenschaftlich gesicherten Erkenntnisse sollen all denen dienen, die sich aktiv und fundiert an den aktuellen Diskussionen im Umfeld der Meeresforschung beteiligen möchten.

Description: Fucus vesiculosus is the most abundant macroalga on hard substrata in shallow waters of the Baltic Sea. In the last decades its population decreased dramatically. It is remarkable that especially the depth dispersal of F. vesiculosus has changed. In order to better understand the reasons for the observed decline it is important to understand the ecology of this alga. Therefore in this work it was tried to observe the ecological role of the biofilm associated with the alga's surface. As it is suspected that this biofilm could have an effect on the further settlement of bacteria and other microorganisms or even larger multi cellular eukaryotic organisms. It was investigated whether the biofilm, separated from the alga, can have an effect on the settlement of microorganisms. For that purpose two new methods were developed and applied. One was using a hydrogel, in which the isolated biofilm was embedded, and served as a settlement substratum for the tested bacteria. The other method was using a polycarbonate bacteriafilter, which was integrated in a self made apparatus, and had the function to separate the biofilm from the settling microorganisms and also to serve as a settlement substratum for the tested bacteria. The results show that the biofilm has a repellent effect on the settlement of the natural microbial colonizer pool while it had an attractant effect on the settlement of the tested culture bacteria, especially on the bacterium which was isolated from the surface of the alga. One further insight of this work was that the method which uses the polycarbonate filters may deliver better results and therefore could be helpful for further investigations.

Description: The brown alga Fucus vesiculosus (Fucales; Fucaceae) has the ability to defend itself against fouling by various species. This antifouling capacity is mediated by a wide range of chemical compounds (Ritschoff, 2000). It is believed that the built up and accumulation of defences against colonisation are costly to the alga (Cronin 2001). Therefore an adaptation by inducing defences dependant on resource availability (Wikstrom &Pavia, 2003 ) and/or demand is expected (Van Alstyne, 1988). In a field trial on the pier of Kiel Fjord we analysed the seasonal variation of antifouling activities of Fucus vesiculosus extracts (individuals from June 2005- May 2006) against the settlement of the barnacle Amphibalanus imrpovisus (Cirripedia; Balanidae ). Additionally we examined a potential relation of fluctuating macrofouling defence abilities to the seasonally varying colonisation pressure of Amphibalanus improvisus (2005-2008). The results reveal a significant variation of the Amphibalanus improvisus settlement rate on extracts of Fucus vesiculosus collected at different months. We could demonstrate that barnacle settlement was significantly higher under the influence of winter algal extracts compared to the settlement under the influence of extracts originating from algae of other months. Although this is according to our expectations that Fucus vesiculosus is least defended against fouling in winter, when the natural colonisation pressure of barnacles is lowest, a significant correlation between barnacle settlement pressure and actual Amphibalanus improvisus settlement on the Fucus vesiculosus extracts could not be proved.

Description: Surfaces of marine macroalgae are exposed to a complex mixture of planktic colonisers in the surrounding seawater. In contrast to artificial substrates surfaces of marine macroalgae are relatively free from settlement of higher eukaryotic organisms, but they are colonised by bacteria. These epibacterial communities alter the algal interface and affect the host alga and further colonisers, respectively. Depending on the composition epiphytic bacteria can be neutral, beneficial or detrimental for its host alga. So far, most data available on bacterial algal interaction was based on cultivable bacterial strains. Thus, only a minor part of bacteria are cultivable, the ecological significance of bacterial algal association was unclear because most of the involved bacteria were not even identified. Therefore it was of substantial importance to fully analyse the composition of the associated epibacterial communities of different macroalgal species Fucus vesiculosus (Phaeophyta), Gracilaria vermiculophylla (Rhodophyta) and Ulva intestinalis (Chlorophyta) by using molecular fingerprinting methods in this thesis. Furthermore, the stability and specificity of algal bacterial associations was evaluated on a seasonal and annual scale. Due to this comprehensive research I could show that only a minor part of the associated bacteria was host specific and seasonally independent, whereas all other presumably commensal bacteria underlies strong shifts in their appearance. I could identify several of these specific bacteria as protective for its host alga, with regard to antibacterial or antilarval activities. Moreover, bacterial classes that are responsible for pathogenesis or to induce further colonisation of higher eukaryotic organisms were underrepresented on algal surfaces, irrespective of the time of year. In parallel I investigated the bacterial colonizer pool that algal surfaces were exposed to and I could demonstrate that Gammaproteobacteria, one of these potential negative bacterial classes, were the most dominate and seasonal independent biofilm forming bacteria on artificial substrates. The observation that algal surfaces are selectively colonised by bacteria suggests a colonisation control at the algal surface. In this thesis I focused on the chemical control of bacterial settlement at the algal surface of the brown alga Fucus vesiculosus. Due to the development of an algal surface extraction method and the investigation of an extract test system in this thesis I was able to mimic the algal surface chemistry on an artificial substrate. Using these techniques I could demonstrate that the surface chemistry of Fucus vesiculosus was responsible for the selective recruitment of bacteria and to shape an algal specific bacterial community even on an artificial substrate that were exposed to the natural bacterial coloniser pool in the marine environment. Finally, I could identify two different compounds within the complex mixture of algal surface metabolites that were responsible to deter the settlement of Gammaproteobacteria from the surface of Fucus vesicu/osus.

Description: Der Klimawandel ist ein aktuelles Thema, das weltweit nicht nur Wissenschaftler beschäftigt. Eine heutzutage schon deutlich messbare Konsequenz des massiven Verbrennens von fossilen Brennstoffen ist die Ozeanversauerung. Seit der Industrialisierung ist der pHWert schon um 0,1 gesunken und es wird um das Jahr 2100 eine Abnahme bis zu 0,4 erwartet, mit der Tendenz bis 2300 sogar um 0,8 Einheiten zu sinken. Wichtig hierbei ist zu untersuchen inwiefern es Organismen und deren Metabolismus beeinträchtigt. Dabei wird sehr stark angenommen, dass kalzifizierende Arten sehr schwer betroffen sind. Diese Arbeit untersucht wie sich die zukünftige Ozeanversauerung auf die Respiration und larvale Entwicklung von Seepockenlarven der Spezies Amphibalanus improvisus auswirkt. Es wurde sich nur auf die sechs Nauplius-Stadien konzentriert und die Cypridlarven oder juvenile Tiere nicht weiter untersucht. Die Larven wurden mit drei verschieden pCO2 behandelt (380, 1120 und 4000 μatm). Es wird vermutet, dass bei erhöhter pCO2-Konzentration der Sauerstoffverbrauch der Larven negativ beeinträchtigt ist und so auch deren larvale Entwicklung verlängert sein könnte.

Description: Over the last 10 years, hydrothermal activity has been shown to be abundant at the ultraslow spreading Arctic Mid-Ocean Ridges (AMOR). Approximately 20 active and extinct vent sites have been located either at the seafloor, as seawater anomalies, or by dredge sampling hydrothermal deposits. Decreasing spreading rates and decreasing influence of the Icelandic hot spot toward the north along the AMOR result in a north-south change from a shallow and magmatically robust to a deep and magmatically starved ridge system. This contrast gives rise to large variability in the ridge geology and in the nature of the associated hydrothermal systems. The known vent sites at the southern part of the ridge system are either low-temperature or white smoker fields. At the deep, northern parts of the ridge system, a large black smoker field has been located, and seawater anomalies and sulfide deposits suggest that black smoker-type venting is common. Several of these fields may be peridotite-hosted. The hydrothermal activity at parts of the AMOR exceeds by a factor of 2 to 3 what would be expected by extrapolating from observations on faster spreading ridges. Higher fracture/fault area relative to the magma volume extracted seems a likely explanation for this. Many of the vent fields at the AMOR are associated with axial volcanic ridges. Strong focusing of magma toward these ridges, deep rifting of the ridges, and subsequent formation of long-lived detachment faults that are rooted below the ridges may be the major geodynamic mechanisms causing the unexpectedly high hydrothermal activity.

Description: Understanding metal and proton toxicity under field conditions requires consideration of the complex nature of chemicals in mixtures. Here, we demonstrate a novel method that relates streamwater concentrations of cationic metallic species and protons to a field ecological index of biodiversity. The model WHAM-FTOX postulates that cation binding sites of aquatic macroinvertebrates can be represented by the functional groups of natural organic matter (humic acid), as described by the Windermere Humic Aqueous Model (WHAM6), and supporting field evidence is presented. We define a toxicity function (FTOX) by summing the products: (amount of invertebrate-bound cation) × (cation-specific toxicity coefficient, αi). Species richness data for Ephemeroptera, Plecoptera and Trichoptera (EPT), are then described with a lower threshold of FTOX, below which all organisms are present and toxic effects are absent, and an upper threshold above which organisms are absent. Between the thresholds the number of species declines linearly with FTOX. We parameterised the model with chemistry and EPT data for low-order streamwaters affected by acid deposition and/or abandoned mines, representing a total of 412 sites across three continents. The fitting made use of quantile regression, to take into account reduced species richness caused by (unknown) factors other than cation toxicity. Parameters were derived for the four most common or abundant cations, with values of αi following the sequence (increasing toxicity) H+ 〈 Al 〈 Zn 〈 Cu. For waters affected mainly by H+ and Al, FTOX shows a steady decline with increasing pH, crossing the lower threshold near to pH 7. Competition effects among cations mean that toxicity due to Cu and Zn is rare at lower pH values, and occurs mostly between pH 6 and 8.

Description: For the eastern tropical Atlantic two recurring El Niño-like phenomena with high interannual SST anomalies have been described, one centered in the equatorial region as part of the Atlantic zonal mode and one off Angola referred to as Benguela Niño. Both events are supposed to be generated not locally but by a relaxation of the trade winds in the western equatorial Atlantic. Here the connection between SST variations in the two regions is investigated with observational data sets as well as ocean model simulations. They are correlated to such an extent that joint events should rather be viewed as one Atlantic Niño. An intriguing feature, counterintuitive in view of the remote forcing mechanism, is that SST anomalies off Angola precede those in the equatorial Atlantic. We show this behavior to be related to the difference in thermocline depths and a different seasonality of interannual SST variability in the two regions. While Benguela Niños peak in austral fall due to the Angola Benguela Front being located furthest to the south and high interannual variability in coastal Kelvin wave activity, warm events at the equator are phase-locked to austral winter when the thermocline is shallow. Perturbation experiments confirm the importance of remote forcing from the equator for SST variability off Angola and demonstrate the leading role of wind stress in the generation of SST anomalies in the eastern tropical Atlantic. These wind stress variations are shown to be linked to fluctuations in the strength of the South Atlantic Anticyclone, a connection that might be important with respect to the predictability of Atlantic Niños.