Linking Seasonal Reduction of Microbial Diversity to Increase in Winter Temperature of Waters of a Chilean Patagonia Fjord

Since microorganisms play a major role in the biogeochemistry of the ocean, understanding structure and dynamics of natural microbial communities is crucial in assessing the impact of environmental changes on marine ecosystems. In order to identify key environmental drivers of microbial community structure in Chilean Patagonian fjords, we analyzed composition of the prokaryotic community over an annual cycle at a single sampling site in Puyuhuapi Fjord. Distinctive communities represented mainly by Actinomycetales, Rhodobacteraceae, Cryomorphaceae, and Flavobacteriaceae were associated with Estuarine Fresh Waters, whereas Cenarchaeaceae and Oceanospirillales were representative of Modified Sub Antarctic Waters present in the fjord. Salinity and oxygen were first-order factors explaining segregation of microbial communities in these contrasting water masses. Positive correlations of members of Flavobacteriaceae, Alteromonadales, and Verrucomicrobiales with diatoms in subsurface waters and of Flavobacteriales (Cryomorphaceae and Flavobacteriaceae), Rhodobacteraceae, and Pelagibacteraceae with dinoflagellates in surface waters suggest that phytoplankton composition could define specific niches for microorganisms in Puyuhuapi fjord waters. A dramatic reduction of richness and individual abundances within Flavobacteriaceae, Rhodobacteraceae, and Cenarchaeaceae families was principally explained by seasonal increase of surface water temperature, with major reduction associated with changes in temperature during winter conditions. Taxa that are sensitive to increased temperature are key components of organic matter and element cycling, and we therefore suggest that potential decrease in diversity associated with rising of surface water temperature could impact current biogeochemical status of Patagonian fjord ecosystems

The influence of glacial cover on riverine silicon and iron exports in Chilean Patagonia

Glaciated environments have been highlighted as important sources of bioavailable nutrients, with inputs of glacial meltwater potentially influencing productivity in downstream ecosystems. However, it is currently unclear how riverine nutrient concentrations vary across a spectrum of glacial cover, making it challenging to accurately predict how terrestrial fluxes will change with continued glacial retreat. Using 40 rivers in Chilean Patagonia as a unique natural laboratory, we investigate how glacial cover affects riverine Si and Fe concentrations, and infer how exports of these bioessential nutrients may change in the future. Dissolved Si (as silicic acid) and soluble Fe (0.45 mu m) phases of both Si and Fe, which are not typically accounted for in terrestrial nutrient budgets but can dominate riverine exports. Dissolved Si and soluble Fe yield estimates showed no trend with glacial cover, suggesting no significant change in total exports with continued glacial retreat. However, yields of colloidal-nanoparticulate and reactive sediment-bound Si and Fe were an order of magnitude greater in highly glaciated catchments and showed significant positive correlations with glacial cover. As such, regional-scale exports of these phases are likely to decrease as glacial cover disappears across Chilean Patagonia, with potential implications for downstream ecosystems

Seasonal changes in dissolved organic matter composition in a Patagonian fjord affected by glacier melt inputs

Biogeochemical processes in fjords are likely affected by changes in surrounding glacier cover but very little is known about how meltwater directly influences dissolved organic matter (DOM) in fjords. Moreover, the data available are restricted to a handful of northern hemisphere sites. Here we analyze seasonal and spatial variation in dissolved organic carbon (DOC) concentration and DOM composition (spectrofluorescence, ultrahigh resolution mass spectrometry) in Baker-Martinez Fjord, Chilean Patagonia (48°S), to infer the impacts of rapid regional deglaciation on fjord DOM. We show that surface layer DOC concentrations do not vary significantly between seasons, but DOM composition is sensitive to differences in riverine inputs. In summer, higher protein-like fluorescence reflects increased glacial meltwater inputs, whilst molecular level data show weaker influence from marine DOM due to more intense stratification. We postulate that the shifting seasonal balance of riverine and marine waters affects the supply of biolabile peptides and organic nitrogen cycling in the surface layer. Trends in DOM composition with increasing salinity are consistent with patterns in estuaries (i.e. preferential removal of aromatic compounds and increasing relative contribution of unsaturated and heteroatom-rich DOM from marine sources). Preliminary estimates also suggest that at least 10 of the annual organic carbon stock in this fjord is supplied by the four largest, glacially fed rivers and that these inputs are dominated by dissolved (84) over particulate organic carbon. Riverine DOC may therefore be an important carbon subsidy to bacterial communities in the inner fjord. The overall findings highlight the biogeochemical sensitivity of a Patagonian fjord to changes in glacier melt input, which likely has relevance for other glaciated fjords in a warming climate

Search for dark matter produced in association with bottom or top quarks in √s = 13 TeV pp collisions with the ATLAS detector

A search for weakly interacting massive particle dark matter produced in association with bottom or top quarks is presented. Final states containing third-generation quarks and miss- ing transverse momentum are considered. The analysis uses 36.1 fb−1 of proton–proton collision data recorded by the ATLAS experiment at √s = 13 TeV in 2015 and 2016. No significant excess of events above the estimated backgrounds is observed. The results are in- terpreted in the framework of simplified models of spin-0 dark-matter mediators. For colour- neutral spin-0 mediators produced in association with top quarks and decaying into a pair of dark-matter particles, mediator masses below 50 GeV are excluded assuming a dark-matter candidate mass of 1 GeV and unitary couplings. For scalar and pseudoscalar mediators produced in association with bottom quarks, the search sets limits on the production cross- section of 300 times the predicted rate for mediators with masses between 10 and 50 GeV and assuming a dark-matter mass of 1 GeV and unitary coupling. Constraints on colour- charged scalar simplified models are also presented. Assuming a dark-matter particle mass of 35 GeV, mediator particles with mass below 1.1 TeV are excluded for couplings yielding a dark-matter relic density consistent with measurements

Primary production studies in the southern bight of the North Sea with reference to Phaeocystis sp. and its adaptation to varying photon flux densities

The ecology of coastal areas in Northern Europe are under pressure as a result of the accumulation of nutrients of terrestrial origin discharged from the Eastern channel to the German Bight. A perceived consequence of this ongoing eutrophication has been an increase in algal activity and a shift in plankton community equilibria. In the Southern North Sea such a shift has given rise to the dominance of the colony forming Pyrmnesiophyte Phaeocystis sp. Well adapted to the turbid, nutrient rich environment, it is now the main primary producer of this region. Subsequently the need to better understand this species, and to be able to measure both more accurately, and interpret more precisely, primary production data, has become of increasing importance. To date the bulk of primary production data comes from in vitro 14-carbon tracer experiments. Increasingly the accuracy of in vitro incubations and the 14-tracer technique has been questioned. In this thesis, a comparative study of in vitro and in situ primary production estimates was undertaken, using the light and dark bottle oxygen Winkler titration technique. The results were compared with 14-carbon derived estimates from the literature. The oxygen and 14-carbon measurements were in the same order of magnitude, however a 50&#37; discrepancy was observed between in vitro and in situ oxygen measurements. The balance between gross production and respiration, expressed as a difference (net community production), or as a ratio (R/Pmax), was observed over the seasonal cycle in the Southern North Sea. It was found that photosynthesis dominated in early April and October, whereas respiration, apparently uncoupled from photosynthesis, peaked in May, when the Phaeocystis bloom had become senescent. An apparent coupling between growth and photosynthetic rates was observed in April. The relationship between growth rate and irradiance in phaeocystis was investigated in the laboratory, and its ability to maintain high growth rates at low photon flux densities was observed. Increase in cellular chlorophyll a concentration and the increase in colony formation were possible photoadaptations of phaeocystis.</p

Estudio de flujos verticales de carbono y nitrógeno en ambientes acuáticos controlados en la bahía de Knebel, Dinamarca utilizando isótopos estables de nitrógeno y carbono (15N y 13C) A study of the vertical flow of carbon and nitrogen in controlled aquatic environments at the Knebel Bay, Denmark, with the use of the stable isotopes of nitrogen and carbon (15N y 13C)

En este estudio se utilizaron isótopos estables como trazadores para caracterizar y cuantificar el flujo vertical de carbono y nitrógeno. Los experimentos se llevaron a cabo en la bahía de Knebel, Dinamarca (56 08' N, 10 11' E), en dos ambientes acuáticos controlados tipo mesocosmos. La adición de nutrientes inorgánicos estimuló el afloramiento del flagelado no-tóxico Prorocentrum minimum, determinando un comportamiento similar en las mediciones de clorofila a (Clo-a), nitrógeno orgánico particulado (NOP) y carbono orgánico particulado (COP) en ambos mesocosmos. Bajo condiciones no limitantes de nutrientes inorgánicos existió una baja discriminación isotópica resultando en bajos valores de delta13C en el COP en suspensión y sedimentado. El desfase entre los máximos de NOP, Clo-a y COP así como la rápida asimilación del nitrato adicionado en menos de tres días y una razón C/N variable indican que P. minimum posee una gran habilidad para asimilar nitrógeno inorgánico. La razón C/N alcanzó un mínimo al inicio del experimento, para luego aumentar una vez agotado el nitrato de la columna de agua. El nitrógeno nuevo sedimentado alcanzó un 10 a 11 % del total originalmente adicionado a la columna de agua en la forma de nitrato, sin que se observara una sedimentación masiva de P. minimum durante los días de duración de este experimento<br>Stable isotopes were used as tracers to characterize and quantify the downward flux of carbon and nitrogen. The experiments were conducted in Knebel bay, Denmark (56 08' N, 10 11' E), in two controlled aquatic environments (mesocosm type). The addition of inorganic nutrients to the mesocosms stimulated a bloom of the non-toxic flagellate Prorocentrum minimum. A similar pattern in the concentration of chlorophyll a (Chl-a), particulate organic nitrogen (PON) and particulate organic carbon (POC) was observed in both mesocosms. The elevated nutrient conditions resulted in low isotopic discrimination, this was reflected in low delta13C values of the suspended and sediment POC. The uncoupling between the peaks of PON, Chl-a and POC, as well as the rapid assimilation of the added nitrate (in less than three days) and a changing C/N ratio indicate that P. minimum has a great ability to assimilate inorganic nitrogen. The C/N ratio reached a minimum at the beginning of the experiment increasing later, once nitrate depletion was reached. The sedimentation of new nitrogen during this study was 10-11 % of the total originally added to the water column. No massive sedimentation of P. minimum was observed once the nitrate added to the mesocosms was utilize

New sponge species from Seno Magdalena, Puyuhuapi Fjord and Jacaf Canal (Chile)

Until now, only 177 species of sponges (Porifera) have been reported for Chilean coastal waters. Here we describe recent scuba diving surveys undertaken to improve our knowledge of the diversity of the sponge fauna of the Seno Magdalena, Puyuhuapi Fjord and Jacaf Canal in Chilean Patagonia. Despite these relatively harsh environments, our study yielded 23 species of Demospongiae, nine of which are new to science and described here: Hymerabdia imperfecta Bertolino, Costa &amp; Pansini sp. nov., Axinella cylindrica Bertolino, Costa &amp; Pansini sp. nov., Axinella coronata Bertolino, Costa &amp; Pansini sp. nov., Biemna aurantiaca Bertolino, Costa &amp; Pansini sp. nov., Biemna erecta Bertolino, Costa &amp; Pansini sp. nov., Biemna typica Bertolino, Costa &amp; Pansini sp. nov., Scopalina cribrosa Bertolino, Costa &amp; Pansini sp. nov., Rhizaxinella strongylata Bertolino, Costa &amp; Pansini sp. nov. and Darwinella pronzatoi Bertolino, Costa &amp; Pansini sp. nov. One species, Hymedesmia (Stylopus) lissostyla (Bergquist &amp; Fromont, 1988), is reported for the first time for Chile.</p

Bacterial growth response to copepod grazing in aquatic ecosystems

The growth rate response of bacterial communities to the potential increase of dissolved organic matter (DOM) produced by the copepod Acartia tonsa was assessed in experiments conducted in three stations representing three contrasting aquatic environments (coastal embayment, shelf and ocean). Bacterial assemblages were inoculated in filtered seawater where A. tonsa had previously grazed. Utilization of DOM over time was evaluated after the addition of bacterial inoculums as the biomass changes in both ‘control’ and ‘copepod’ treatments. In the embayment and ocean a high bacterial growth was observed in the treatments with seawater where copepod were feeding. Additional field measurements of bacterial, primary production and zooplankton biomass support the idea that bacterial communities living in oceanic environments can be efficient to utilize the newly available substrate. Copepods play a key role not only as conveyors of carbon up through the classical food-web, but also generated significant amounts of bacterial substrate in the microbial loop food-web

New sponge species from Seno Magdalena, Puyuhuapi Fjord and Jacaf Canal (Chile)

Until now, only 177 species of sponges (Porifera) have been reported for Chilean coastal waters. Here we describe recent scuba diving surveys undertaken to improve our knowledge of the diversity of the sponge fauna of the Seno Magdalena, Puyuhuapi Fjord and Jacaf Canal in Chilean Patagonia. Despite these relatively harsh environments, our study yielded 23 species of Demospongiae, nine of which are new to science and described here: Hymerabdia imperfecta Bertolino, Costa & Pansini sp. nov., Axinella cylindrica Bertolino, Costa & Pansini sp. nov., Axinella coronata Bertolino, Costa & Pansini sp. nov., Biemna aurantiaca Bertolino, Costa & Pansini sp. nov., Biemna erecta Bertolino, Costa & Pansini sp. nov., Biemna typica Bertolino, Costa & Pansini sp. nov., Scopalina cribrosa Bertolino, Costa & Pansini sp. nov., Rhizaxinella strongylata Bertolino, Costa & Pansini sp. nov. and Darwinella pronzatoi Bertolino, Costa & Pansini sp. nov. One species, Hymedesmia (Stylopus) lissostyla (Bergquist & Fromont, 1988), is reported for the first time for Chile