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Blanche Saint Béat (Takuvik, Québec) seminar

Blanche Saint Béat, a researcher at Takuvik, a joint CNRS/Université Laval international laboratory in Quebec that studies Arctic ecosystems, will present her work on Monday, June 24 at 11 am at IUEM in room A215.

Ecosystems passed to the revelator of network analysis.

Plankton, which is at the base of the pelagic food web, has an essential role in 1) the carbon cycle through biological, lipid and microbial pumps, and 2) as a buffer for environmental variability, necessary to maintain fish resources. In the context of climate change and increasingly high societal challenges, a detailed understanding of the processes structuring food webs and governing their functioning is essential. Over the past few decades, ecological network analysis (ENA) and associated indices have been developed to address these new issues. Indeed, these indices objectively qualify and quantify the emerging properties (not visible in situ) of the ecosystem. These properties, resulting from interactions between species, determine the distribution of carbon through the different flows of the network and characterize the functioning of ecosystems. The ENA indices thus make it possible to discriminate between the functioning of different ecosystems and/or different states within the same ecosystem. The performance of network analysis has made it a very popular tool in ecosystem management and monitoring. However, the robustness of these indices depends on the quality of the carbon flow estimation. Despite the increasing number and performance of instruments deployed in the field, it is almost impossible to measure all in situ flows. Modelling, and more particularly inverse linear modelling, is used to estimate the values of these flows. The performance of these models must be analyzed, verified and improved if necessary. In such studies, the ENA indices are relevant as a validation tool. By providing a global vision of ecosystems, they make it possible to validate ecosystem properties simulated by the models. Thus, whether through ecological or methodological applications, ENA indices are very useful. Examples from my thesis and post-doctoral work will illustrate and discuss the interest of this method and its wide range of applications, both in terms of the issues addressed (stability pattern, sensitivity to integrated information, discrimination of ecosystems, etc.) and the ecosystems studied (intertidal, pelagic, lacustrine, etc.).

Page de Blanche Saint Béat: http://www.takuvik.ulaval.ca/team/blanche_stbeat.php

Takuvik Laboratory website: http://www.takuvik.ulaval.ca/index.php

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Monday, June 24 at 11 am at IUEM in room A215

Seminar by Julie Laroche, Professor at Dalhousie University (Canada) on Tuesday, May 28

Julie LaRoche, is a visiting professor at LEMAR as part of the OFI and EUR ISBlue, will hold a seminar on Tuesday 28 May at IUEM in amphitheatre D from 11:00 am.

Julie LaRoche, is professor and Canada Research Chair in Marine Microbial Genomics and Biogeochemistry, Department of Biology, Dalhousie University, Nova Scotia, Canada.

The title of her presentation will be: Dynamics of microbial community structure and marine dinitrogen fixation at a microbial observatory in the Northwest Atlantic Ocean.

Abstract:
Primary productivity is limited by the availability of fixed nitrogen in large regions of the oceans. Dinitrogen fixation, the only biological input pathway into the marine N cycle, is an energetically expensive biochemical process that reduces N2 gas into NH3, a form of fixed nitrogen that is readily incorporated into biomolecules. The nitrogen fixers, or diazotrophs, are a selected group of prokaryotic microorganisms that can carry out this biochemical process. Historically, marine nitrogen fixation was thought to be a process carried out primarily by cyanobacteria and important mainly in the tropical and subtropical oligotrophic waters. Recent realization concerning the wide diversity of marine microbes harboring the nitrogenase enzyme indicates that we do not fully understand the roles of the diverse diazotrophs that populate the ocean. In the context of the Ocean Frontier Institute located at Dalhousie University, the microbial community structure and function in Northwest Atlantic (NWA) have been assessed through next-generation sequencing of hypervariable regions of 16S and 18S rRNA genes, nifH gene and metagenomics at existing time-series stations since 2014. The nifH gene, a marker gene for diazotrophy, has shown that both cyanobacterial and non-cyanobacterial diazotrophs are members of the microbial communities in our NWA microbial observatories. The lecture will focus on the microbial community structure in the NWA, with a specific attention to the diazotrophs. In particular, the potential metabolic pathways identified from the genome annotation of a novel bacterial isolate, belonging to a clade of gamma-proteobacteria widely distributed in the Tara expedition database, will be discussed in a global context.

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Conference by Philippe Calvez (Institut de Biologie Structurale de Grenoble) on may 6th 2019

Philippe Calvez, who has just finished a postdoctoral fellowshipat the Institut de Biologie Structurale à Grenoble will be in Brest on monday may 6th 2019 and will give a seminar à 11:00 in amhi D :

Membrane : Interplay Between Physics and Biology

or Cooperation of membranes physical properties in biological processes

 

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Seminar by Vena Haynes (University of Connecticut, USA). Next Friday, May 17

We are currently hosting Vena Haynes at LEMAR, who is doing her thesis at the University of Connecticut and will present her research on the toxicity of titanium nanoparticles to planktonic organisms on Friday, May 17 at 11am in A215 (IUEM).

Investigating the phototoxic effects of titanium dioxide nanoparticles on a marine planktonic food web

Summary

In this presentation, I will discuss parts of my dissertation research done at the University of Connecticut, Department of Marine Sciences and the collaborative research I will do here at LEMAR as part of my Chateaubriand Fellowship. The objective of my dissertation is to investigate the impact of titanium dioxide nanoparticles (n-TiO2) on a marine planktonic food web, under conditions similar to those found in the photic zone of near shore waters. TiO2 nanoparticles are found in paints, sunscreens, and personal care products and enter the marine environment through run-offs, product usage and industrial wastewater. Additionally, TiO2 is highly photoactive, and generates reactive oxygen species (ROS) when exposed to ultraviolet (UV) radiation. There is some evidence of its phototoxicity to aquatic organisms in freshwater systems, but its effects in the marine environment are poorly understood. This research addresses the effects of n-TiO2 and light on the following: a) abundance and metabolic function of heterotrophic bacteria and microalgae associated with marine aggregates, b) mortality, egg production and hatching success of the Calanoid copepod Acartia tonsa, and c) mortality and growth of gastropod (Crepidula fornicata) larvae.

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Daniel Conley’s seminar (Lund University, Sweden) on April 29

On April 29th at 10am in room A215 (IUEM) we will welcome Daniel Conley from Lund University in Sweden who will present his work on the following theme:

Constraining variations in the global biogeochemical silica cycle through geologic time.

Summary of his presentation:

It is widely recognized that the emergence and expansion of silica biomineralization in the oceans has affected evolutionary competition for dissolved Si (DSi). This resulted in changes in the global biogeochemical cycles of silica, carbon (C) and other nutrients that regulate ocean productivity and ultimately climate. However, a series of very recent discoveries in geology and biology suggest that the first biological impacts on the global Si cycle were likely by prokaryotes during the Archean with further decreases in oceanic DSi with the evolution of widespread, large-scale skeletal biosilicification significantly earlier than the current paradigm. Our project interweaves geology and biology and will create new knowledge into the interactions between biosilicification in organisms and the environment and how these interactions have evolved through Earth’s history. Together, these geological and biological analyses will provide novel insights into the key events during periods of DSi drawdown, which reorganize the distribution of carbon and nutrients, changing energy flow and productivity in the biological communities of the ancient oceans.

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