ALBERT

Description: Herbivory can modify seaweed community structure by affecting variation in the abundance and distribution over spatial and temporal scales. To deter herbivores, seaweeds have developed several mechanisms, including the induction of chemical and morphological defenses, which may be influenced by environmental factors such as nutrient availability. In two sets of experiments 5 red, 4 brown, and 1 green seaweeds were tested for inducible defenses following exposure to direct consumption by an amphipod community. In addition, the effects of consumer presence and neighborhood grazing (indirect consumption) on the induction of defenses were examined in the red seaweed Gracilaria cearensis and the green seaweed Codium decorticatum under natural and additionally 100% elevated nutrient levels for C. decorticatum. In preliminary studies, suitable organisms for the induction experiments were determined in testing survival of potential tropical algae from the Brazilian littoral under laboratory conditions and performing multiple-choice feeding assays for four important Brazilian herbivore species in order to determine their preference rankings of these algae. The amphipod community dominated by Elasmopus brasiliensis was identified as the most suitable grazers. Induction of defense was evaluated after consumer exposure in choice-feeding experiments by offering live algae (LA, total defense) and reconstituted food (RF, chemical defense) of previously consumed (treated) and unconsumed algae (control). Nutrient enrichment did not affect induction of defense in C. decorticatum, yet unfertilized seaweeds were more palatable relatively to fertilized conspecifics. Different consumer activities did not affect palatability in G. cearensis, yet C. decorticatum seemed to induce resistance (LA) after reception of waterbome cues from consumed conspecifics. Unexpectedly C. decorticatum RF exhibited higher susceptibility to amphipods after consumer exposure in both experiments performed. While no significant decrease in palatability was observed in previously consumed algae compared to unconsumed controls after one week, two red seaweeds, Chondrophycus flagellifera (RF) and Pterocladiella capillacea (LA), exhibited significantly reduced palatability after consumer exposure. The brown seaweed Lobophora variegata showed significantly retarded chemical resistance after three weeks. This is the first report of inducible chemical defense in a red seaweed.

Description: The objective of this study is to reconstruct past environmental settings locked in the sediments of a carbonate mound in the northern Porcupine Seabight, west off Ireland. Benthic foraminiferal assemblages were investigated on two sediment cores, one located on top of the mound and a second one from an off-mound position further north as control site. The off-mound samples reveal two different assemblages: (1) an Interglacial group dominated by infaunal species, and (2) a Glacial group, dominated by cassidulinid species. Due to an incomplete stratigraphic record in the on-mound core, same species of the off-mound assemblages were grouped in on-mound samples. The Interglacial group dominates and the Glacial group is less abundant throughout the entire core indicating the lack of glacial time intervals in the on-mound core, which is coherent with stable oxygen isotope data and U/Th dates on coral fragments. A third assemblage is abundant in samples of the on-mound core showing elevated epibenthic species. This Mound group shows a great affinity to strong currents, high nutrient availability and is supposed to indicate Mediterranean Outflow Water in the northern Porcupine Seabight, as well as a higher coral cover on Propeller Mound in an earlier interglacial period. A Late Pleistocene decline in mound growth for Propeller Mound is suggested by the decrease of the Mound group towards the Holocene. Finally, the reconstructed environmental setting portrays the boundary conditions of the habitable range for the cold-water corals. Their growth occurred during interglacial and interstadial periods, whereas a glacial retreat of corals is documented in the absence of glacial sediments in the on-mound core. These conclusions are summarised in a model which efficiently accounts for the mound development covering the period of the Northern Hemisphere Glaciation.

Description: Im Zuge dieser Arbeit konnte das Promotor-Testsystem mit dem Vektor pRL488 erfolgreich etabliert werden. Im Einzelnen wurden folgende Punkte bearbeitet: 1. Die Transformation von Anabaena sp. PCC 7120 mit Hilfe der Elektroporation konnte erfolgreich etabliert werden und war bei 10 kV fiir 2 ms optimal. 2. Die DNA-Fragmente aus den Bereichen vor nifH (Abb.16) und petE (Abb.16) wiesen im Vergleich zur Hintergrundaktivität des pRL488 keine signifikant erhöhte Promotoraktiviät auf (Abb. 29 und Abb.30). Dies lässt vermuten, dass in beiden Fällen die klonierten Fragmente nicht den vollständigen Promotor enthielten und entscheidende Transkriptionsfaktorbindestellen fehlten. Da bisher kaum Promotorstudien an Cyanobakterien durchgeführt wurden, schien zu Beginn dieser Arbeit eine GröBe von 700 bis 1100 bp im Vergleich zu typischen Promotoren in E.coli wie Ptac, Ptrp und Para (Lewin, 2000) ausreichend zu sein. In diesen Fällen müssen jedoch die Promotoren mehr als 870 bp umfassen. 3. Nur in Kulturen, die unter Stickstoffmangel angezogen wurden konnte eine Aktivität der aufnehrnenden Hydrogenase gemessen werden (Abb.26) Diese Enzymaktivität kann daher als Marker für die Bildung von Heterocysten angesehen werden. Die Aktivität der bidirektionalen Hydrogenase ist in Kulturen mit Heterocysten deutlich höher (Abb.27). Inwieweit dies auf eine verstärkte Expression des Enzyms in den Heterocysten zuruckzuführen ist, sollte uber weitergehende zellspezifische Promotoranalysen geklärt werden. 4. Unter den DNA-Fragementen aus den Genclustern der bidirektionalen Hydrogenase (vor alr0760, vor hoxU und hoxH) hatte nur das Fragment vor dem Leserahmen alr0760 eine deutliche Promotoraktivität (Abb.34), während die Bereiche vor hoxU und hoxH nicht von der Aktivität der Kontrolle zu unterscheiden sind (Abb.31). Dieses Ergebnis spricht dafür, dass die Transkription aller Gene von alr0760 bis hoxH in diesem Cluster von einem Promotor vor alr0760 gesteuert wird und entsprechend diese Gene auf einem Transkript liegen. 5. Zur Herstellung eines Promotor-Testsystems mit GFP wurden zwei verschiedene Klonierungsstrategien entwickelt und ein Vektorkonstrukt zur Insertion des gfp-Gens in den pRL488 konstruiert.

Description: Polychaete meroplanktonic larvae from the List tidal basin were identified, their horizontal and vertical distribution patterns described, and temporal abundance fluctuations analyzed. Tides cause marked changes in the depth of this basin, while seasonality and weather dependence cause high environmental and biological variability. The taxonomic composition was analyzed from samplings undertaken between 1996-2002, during flood and ebb periods. Spionid, phyllodocid, and polynoid larvae are representative for this basin, accounting 60% of the total number of taxa (46 taxa). The larval production is numerically dominated by Pygospio elegans, Spio martinensis, Polydora cornuta and Lanice conchilega. Since their benthic stages are well known inside the basin, a large proportion of the larval production can be considered local. The low correspondence between benthic and planktonic assemblages suggested a qualitatively important input of long-distance larval vagrants. Sites within the basin differed in species composition, suggesting that larvae are not randomly mixed by the tidal hydrodynamics. Polychaete larvae are retained inside the basin, in spite of the continuous exchange of water with the North Sea. Analyses of the spatial distribution undertaken at three spatial scales during flood and ebb periods indicated that benthic occurrence, coastal morphology, and larval behavior could enhance species-specific distribution patterns. Significant fluctuations in total and partial larval abundances occurred between 1996-2001 were probably related to variables with influence over gonadal maturation and spawning in adult stages, as well as larval feeding and performances.

Description: This PhD thesis was part of the EU-funded project CAVASSOO (Carbon Variability Studies by Ships of Opportunity). The major goal of the project was to establish an international network in the North Atlantic consisting of commercial vessels that are equipped with pC02 measurement devices. The installation of a autonomously working pC02 unit onboard the carcarrier M/V Falstaff was completed in January, 2002. Measurements started a month later with the first transatlantic crossing. In the following months continuous and discrete samples were analyzed. It was examined whether it is possible to correlate the oceanic pC02 with parameters that can be retrieved by ship-independent observations such as remote sensing. The correlatin between pC02 and nitrate was promising in this context and it could also be shown that nitrate correlated well with the mixed layer depth. Parameters such as temperature and chlorophyll on the other hand did not reveal a unique correlation with the pC02. Within this thesis it was also shown that the seawater pC02 in the eastern basin (l0 °W-35 °W) showed smaller seasonal changes than in the western basin (36°W-70 °W) in the North Atlantic. This was explained by the fact that in the eastern basin the temperature effect on the seawater pC02 was counteracted by the biological effect yielding a damped easonal pC02 cycle. In the western basin, however, temperature was the major force on the pC02 which was not reduced by a counteracting biology effect thus yielding a pronounced seasonal pC02 cycle. The C02 flux calculation showed that this region of the North Atlantic was a sink for atmospheric C02 in 2002. When comparing the C02 flux to a well-cited pC02 climatology the difference was small (4%). The seasonal cycles of nutrients within different watermasses showed distinct patterns. The C:N ratio of the seasonal new production were similar to the Redfield ratio for all watermasses excecpt for the Gulfstream watermass. In the latter a carbon overconsumption with respect to Redfield could be shown which pointed at N2 fixation. This result was underlined by the high N:P values of the Gulfstream waters.