ALBERT

Description: The earliest diagenetic post-mortem exposure of biogenic carbonates at the sea floor and in the uppermost sediment column results in the colonization of hard-part surfaces by bacterial communities. Some of the metabolic redox processes related to these communities have the potential to alter carbonate shell properties, and hence affect earliest diagenetic pathways with significant consequences for archive data. During a three-month in vitro study, shell subsamples of the ocean quahog Arctica islandica (Linnaeus, 1767) were incubated in natural anoxic sediment slurries and bacterial culture medium of the heterotrophic Shewanella sediminisHAW-EB3. Bulk analyses of the liquid media from the Shewanella sediminis incubation revealed an over ten-fold increase in total alkalinity, dissolved inorganic carbon and ΩAragonite, and the alteration of the Mg/Ca, Mg/Sr and Sr/Ca ratios relative to control incubations without cultures. Ion ratios were most affected in the incubation with anoxic sediment, depicting a 25% decrease in Mg/Ca relative to the control. Shell sample surfaces that were exposed to both incubations displayed visible surface dissolution features, and an 8 wt% loss in calcium content. No such alteration features were detected in control shells. Apparently, alteration of shell carbonate properties was induced by microbially driven decomposition of shell intercrystalline organic constituents and subsequent opening of pathways for pore fluid-crystal exchange. This study illustrates the potential influence of benthic bacterial metabolism on biogenic carbonate archives during the initial stages of diagenetic alteration within a relatively short experimental duration of only three months. These results suggest that foremost the biological effect of bacterial cation adsorption on divalent cation ratios has the potential to complicate proxy interpretation. Results shown here highlight the necessity to consider bacterial metabolic activities in marine sediments for the interpretation of palaeo-environmental proxies from shell carbonate archives.

Description: Lateralization is widespread throughout the animal kingdom [1; 2; 3; 4; 5; 6 ; 7] and can increase task efficiency via shortening reaction times and saving on neural tissue [8; 9; 10; 11; 12; 13; 14; 15 ; 16]. However, lateralization might be costly because it increases predictability [17; 18; 19; 20 ; 21]. In predator-prey interactions, for example, predators might increase capture success because of specialization in a lateralized attack, but at the cost of increased predictability to their prey, constraining the evolution of lateralization. One unexplored mechanism for evading such costs is group hunting: this would allow individual-level specialization, while still allowing for group-level unpredictability. We investigated this mechanism in group hunting sailfish, Istiophorus platypterus, attacking schooling sardines, Sardinella aurita. During these attacks, sailfish alternate in attacking the prey using their elongated bills to slash or tap the prey [ 22; 23 ; 24]. This rapid bill movement is either leftward or rightward. Using behavioral observations of identifiable individual sailfish hunting in groups, we provide evidence for individual-level attack lateralization in sailfish. More strongly lateralized individuals had a higher capture success. Further evidence of lateralization comes from morphological analyses of sailfish bills that show strong evidence of one-sided micro-teeth abrasions. Finally, we show that attacks by single sailfish are indeed highly predictable, but predictability rapidly declines with increasing group size because of a lack of population-level lateralization. Our results present a novel benefit of group hunting: by alternating attacks, individual-level attack lateralization can evolve, without the negative consequences of individual-level predictability. More generally, our results suggest that group hunting in predators might provide more suitable conditions for the evolution of strategy diversity compared to solitary life.

Description: Methods for measuring aerobic methane oxidation (MOx) rates in aquatic environments are often based on the incubation of water samples, during which the consumption of methane (CH4) is monitored. Typically, incubation vessels are sealed with butyl rubber because these elastomers are essentially impermeable for gases. We report on the potential toxicity of five different commercially available, lab-grade butyl stoppers on MOx activity in samples from marine and lacustrine environments. MOx rates in incubations sealed with non-halogenated butyl were 〉 50% lower compared to parallel incubations with halogenated butyl rubber stoppers, suggesting toxic effects associated with the use of the non-halogenated butyl type. Aqueous extracts of non-halogenated butyl rubber were contaminated with high amounts of various organic compounds including potential bactericides such as benzyltoluenes and phenylalkanes. Comparably small amounts of organic contaminants were liberated from the halogenated butyl rubber stoppers but only two halogenated stopper types were found that did not seem to leach any organics into the incubation medium. Furthermore, the non-halogenated and two types of the halogenated butyl elastomers additionally leached comparably high amounts of zinc. While the source of the apparent toxicity with the use of the non-halogenated rubber stoppers remains elusive, our results indicate that leaching of contaminants from some butyl rubber stoppers can severely interfere with the activity of MOx communities, highlighting the importance of testing rubber stoppers for their respective contamination potential. The impact of leachates from butyl rubber on the assessment of biogeochemical reaction rates other than MOx seems likely but needs to be verified.

Description: Highlights • Polypropylene and biodegradable plastic bags were incubated in marine sediments. • Bacterial colonization was highest on biodegradable plastic bags. • None of the two bag types showed signs of degradation after 98 days. • Marine sediments probably represent a long-term sink for both types of litter. Abstract To date, the longevity of plastic litter at the sea floor is poorly constrained. The present study compares colonization and biodegradation of plastic bags by aerobic and anaerobic benthic microbes in temperate fine-grained organic-rich marine sediments. Samples of polyethylene and biodegradable plastic carrier bags were incubated in natural oxic and anoxic sediments from Eckernförde Bay (Western Baltic Sea) for 98 days. Analyses included (1) microbial colonization rates on the bags, (2) examination of the surface structure, wettability, and chemistry, and (3) mass loss of the samples during incubation. On average, biodegradable plastic bags were colonized five times higher by aerobic and eight times higher by anaerobic microbes than polyethylene bags. Both types of bags showed no sign of biodegradation during this study. Therefore, marine sediment in temperate coastal zones may represent a long-term sink for plastic litter and also supposedly compostable material.

Description: Calcium carbonates (CaCO32-­‐) belong to the most common mineral groups within the marine realm. In this thesis interactions between marine microbes and carbonate stability are investigated in depth. Microbial biofilms are analyzed at high resolution regarding their functions in element and isotopic fractionation. In addition, calcite dissolution experiments were carried out to quantify the effect of aerobic methane oxidizing bacteria. Carbonate precipitation rates in marine sediments often serve as a fitting parameter for numerical modeling approaches to constrain. 45Ca and 14C-bicarbonate incubation experiments were carried out to quantify ongoing calcification in natural sediment slurries. During a research cruise rates of anaerobic methane oxidation and sulfate reduction were determined for the first time using radiotracers. The obtained rates were combined with carbonate isotopic signatures to elucidate local variations of fluid advection.

Description: Sulfate-reducing bacteria are known to mediate dolomite formation under hypersaline conditions, but details of the crystal nucleation process are still poorly constrained. Our laboratory study demonstrates for the first time that Desulfobulbus mediterraneus, a marine sulfate-reducing bacterium, mediates primary precipitation of Mg-rich dolomite under anoxic conditions in media replicating modern seawater chemistry at low temperature (21 °C). Precipitation of crystals was associated with extracellular polymeric substances in a monospecific biofilm, providing templates for nucleation by altering the molar Mg/Ca ratio. After initial nucleation of single nanospherulites (∼50 nm), growth was mediated by aggregation, resulting in spherulites of ∼2–3 μm in diameter. Nucleation led to differences in Mg/Ca ratios and δ44/40Ca values among the organic material (i.e., biofilm including cells and extracellular polymeric substances; 0.87 ± 0.01 [2 SD] and 0.48‰ ± 0.11‰ [2 SE], respectively), the crystals (1.02 ± 0.11 [2 SD] and 〈−0.08‰ ± 0.24‰ [2 SE], respectively), and the liquid bulk medium after mineral precipitation (4.53 ± 0.04 [2 SD] and 1.10‰ ± 0.24‰ [2 SE], respectively). These data indicate a two-step fractionation process involved in the sequestration of Ca from the solution into the crystal lattice of the mineral precipitated. Our results demonstrate the capability of extracellular polymeric substances to overcome kinetic inhibition, fostering the formation of kinetically less favorable Mg-rich dolomite, and they also question the applicability of the Ca isotopic system as a proxy for paleogeochemistry of seawater.