Experiment: summer mortality phenomena in pacific oysters

Mass mortalities of Pacific oysters Crassostrea gigas occur regularly when temperatures are high. Elevated temperatures facilitate the proliferation and spread of pathogens and simultaneously impose physiological stress on the host. Additionally, periods of high temperatures coincide with the oyster spawning season. Spawning is energetically costly and can further compromise oyster immunity. Most studies monitoring the underlying factors of oyster summer mortality in the field, point to the involvement of abiotic and biotic factors including low salinities, high temperatures, pollutants, toxic algae blooms, pathogen exposure and physical stress in conjunction with maturation. However, studies addressing more than two factors experi- mentally are missing thus far. Therefore, we investigated the combination of three main factors including abiotic as well as internal and external biotic stressors by conducting controlled infection experiments on pre-and post-spawning as well as on gravid oysters with opportunistic Vibrio sp. at two different tempera- tures. Based on mortality rates, infection intensity and cellular immune parameters, we provide experimental evidence that all three factors (i.e. reproductive investment, elevated temperatures and infection with oppor- tunistic Vibrio sp.) act additively to the phenomenon of oyster summer mortality, leaving post-spawning oyster more susceptible to SMS than pre-spawning and gravid oysters. While previous studies found that post-spawning oysters have a lower thermal tolerance and a reduced ability to withstand pathogen infec- tions, our study now allows to separate the relative contribution of different causative agents to oyster sum- mer mortality and pinpoint to infection with pathogenic Vibrio sp. being of highest importance. In addition we can add a mechanistic understanding for the higher losses after spawning during which the phagocytic ability of hemocytes was strongly impeded resulting in insufficient clearance of pathogens.

Palynological investigations of profile Cergowa in Poland

The decomposition rate of organic, Compounds, following the death of a plant, is dependent on several external factors. Assimilatory pigments generally undergo a rapid degradation. In certain condition, however, their decomposition may be considerably retarded; e.g. compounds similar to chlorophyll and some carotenoids, as a and ß-carotene, lutein and others, may persist several thousand years in marine and lake Sediments (Vallentyne 1960). Derivatives of chlorophyll were also found in the surface layer of wood soil (Gorham 1959). In this connection the question arises, in what a way a still different environment, namely peat, influences the decomposition rate of pigments. The starting point in these investigations was the fact observed by one of the co-authors, that many subfossil fir needles from various depths of the peat bog in Cergowa Gora were bright yellow green pigmented. Macroscopic otoservations have already suggested that, at least, a part of the pigments did not undergo decomposition. A study was undertaken with the aim to determine the quantitative and qualitative changes in assimilatory pigments, occurring in fir needles in dependence on the pexiod of time they were lying in the peat bog.

Geochemistry of sediments from the Eastern Cape Basin

Sediment cores retrieved in the Benguela coastal upwelling system off Namibia show very distinct enrichments of solid phase barium at the sulfate/methane transition (SMT). These barium peaks represent diagenetic barite (BaSO4) fronts which form by the reaction of upwardly diffusing barium with interstitial sulfate. Calculated times needed to produce these barium enrichments indicate a formation time of about 14,000 yr. Barium spikes a few meters below the SMT were observed at one of the investigated sites (GeoB 8455). Although this sulfate-depleted zone is undersaturated with respect to barite, the dominant mineral phase of these buried barium enrichments was identified as barite by scanning electron microscopy (SEM). This is the first study which reports the occurrence/preservation of pronounced barite enrichments in sulfate-depleted sediments buried a few meters below the SMT. At site GeoB 8455 high concentrations of dissolved barium in pore water as well as barium in the solid phase were observed. Modeling the measured barium concentrations at site GeoB 8455 applying the numerical model CoTReM reveals that the dissolution rate of barite directly below the SMT is about one order of magnitude higher than at the barium enrichments deeper in the sediment core. This indicates that the dissolution of barite at these deeper buried fronts must be retarded. Thus, the occurrence of the enrichments in solid phase barium at site GeoB 8455 could be explained by decreased dissolution rates of barite due to the changes in the concentration of barite in the sediment, as well as changes in the saturation state of fluids. Furthermore, the alteration of barite into witherite (BaCO3) via the transient phase barium sulfide could lead to the preservation of a former barite front as BaCO3. The calculations and modeling indicate that a relocation of the barite front to a shallower depth occurred between the last glacial maxium (LGM) and the Pleistocene/Holocene transition. We suggest that an upward shift of the SMT occurred at that time, most likely as a result of an increase in the methanogenesis rates due to the burial of high amounts of organic matter below the SMT.

Pteropod eggs released at high pCO2 lack resilience to ocean acidification

The effects of ocean acidification (OA) on the early recruitment of pteropods in the Scotia Sea, was investigated considering the process of spawning, quality of the spawned eggs and their capacity to develop. Maternal OA stress was induced on female pteropods (Limacina helicina antarctica) through exposure to present day pCO2 conditions and two potential future OA states (750??atm and 1200??atm). The eggs spawned from these females, both before and during their exposure to OA, were incubated themselves in this same range of conditions (embryonic OA stress). Maternal OA stress resulted in eggs with lower carbon content, while embryonic OA stress retarded development. The combination of maternal and embryonic OA stress reduced the percentage of eggs successfully reaching organogenesis by 80%. We propose that OA stress not only affects the somatic tissue of pteropods but also the functioning of their gonads. Corresponding in-situ sampling found that post-larval L. helicina antarctica concentrated around 600?m depth, which is deeper than previously assumed. A deeper distribution makes their exposure to waters undersaturated for aragonite more likely in the near future given that these waters are predicted to shoal from depth over the coming decades.