trophic web – Laboratoire LEMAR UMR 6539

New insights into trophic ecology

Understanding how ecosystems function depends on our ability to identify the pathways by which energy and matter move through communities. This description is complicated in the marine environment by (1) the microscopic nature of the sources ingested by many organisms, (2) the spatial and temporal variability of the diet of organisms, (3) the high mobility of many species, which have the ability to find food in many different habitats, and (4) the highly opportunistic nature of many species from a dietary perspective. Understanding trophic relationships within ecosystems thus requires our ability to study these relationships empirically in the natural environment, to describe the forcing variables via experimentation, and to understand the consequences, from the organism to the ecosystem, via modelling approaches. In this context, LEMAR has undergone strong development over the past few years with the recruitment of researchers, teacher-researchers, engineers and technicians, and the development of analytical platforms giving it an unrivalled capacity in France in the field of isotope and lipid analysis applied to the marine environment, as well as in the field of bioenergetic and ecosystem modelling. These approaches are now used in all marine environments, coastal and offshore, polar, temperate and tropical, on numerous biological models and habitats, and will continue to develop over the next few years; they will provide new perspectives for understanding the functioning of marine ecosystems and organisms.

05/10/2018/by sherve@univ-brest.fr

Functional ecology

Discovery-thematic, research thematic

Understanding the role and functions of organisms in their living environment is a major objective set by the DISCOVERY team. To simplify the representation of biodiversity and its role in the functioning of ecosystems, a functional approach to biodiversity is used by looking for groups of species, characterised by common biological traits (trophic mode, mobility, sediment reworking, bioirrigation, etc.) that have homologous effects on key ecological functions (e.g. food webs, primary production, photosynthesis, biogeochemical fluxes, bioturbation, etc.). Particular attention will be paid to the variability of biological traits (functional redundancy) in response to biotic and abiotic interactions, and to the study of interactions between functional groups (facilitation, complementarity, inhibition, competition) in order to appreciate the complexity of communities. This information will enable us to conceptualise, develop and parameterise models of community structuring and ecosystem functioning.

05/10/2018/by sherve@univ-brest.fr

Carbon fate in the deep ocean

Chibido-thematic, research thematic

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The biological carbon pump can be broken down into three stages: the formation of biogenic carbon at the surface (production), the transfer below the mixed layer (export) and the attenuation of the flux in the mesopelagic zone (200-2000 m), towards long-term storage (> 1000 years) in the deep ocean and sediments. For operational reasons, the years 1980-2000 were strongly focused on the first two components of the biological pump (international JGOFS programme). The depth of carbon flux attenuation with depth, which imposes strong constraints on the time scales of carbon storage in the deep ocean, is constrained by ocean dynamics (turbulence, small scales, etc.), dissolution processes, biological activity (heterotrophic activity, respiration) and particle behaviour (sedimentation, aggregation/desaggregation). The evolution of observation means (autonomous platforms, high frequency measurements, acoustics, imaging, molecular biology, etc.), as well as progress in modelling (computer power, taking complexity into account, Artificial Intelligence), now make it possible to tackle this question head-on. LEMAR is fully involved in this new dynamic and relies on its expertise in the description of the fate of dissolved organic matter, the silicon, iron and carbon cycles, the role of zooplankton, remineralisation processes, particle dynamics, the study of the small scale in the mesopelagic zone (see AR2. 1 CHIBIDO), modelling (in connection with the ITM Atlantic teams developing approaches in Artificial Intelligence), microbiology or ecology to get involved and carry out international projects on this topic. In addition, the laboratory actively participated in the creation of the international consortium JETZON (Joint Exploration of the Twilight Zone Ocean Network: https://jetzon.org/) coordinating programmes on the mesopelagic zone.

05/10/2018/by sherve@univ-brest.fr

The ocean dynamics is structured on scales ranging from a thousand kilometers, a few meters, through the tens / hundreds of kilometers.

Ecology and physiology of photosynthetic organisms

Context

As a “primary” biomass, phytoplankton and microphytobenthos are widely involved in the functioning of trophic chains, in the dynamics of biogeochemical cycles and ocean-atmosphere exchanges, which makes them an important and transverse subject of study for LEMAR teams. Quantitative and qualitative fluctuations in phytoplankton communities depend on physical, chemical and biological factors in the rapidly changing environment under the pressure of human activities. Knowledge in this field is now limited to the description of some of the “major” phenomena: seasonal fluctuation and succession of species, specific blooms… Studies highlight significant disturbances of these communities under the influence of anthropogenic forcings such as increased land inputs (e.g. trace metals, Fe, Cu, Co), increased atmospheric CO2 and temperature. The spatial and temporal evolution of the phytoplankton and microphytobenthic community resulting from this, such as the development of toxic micro-algae blooms, directly impacts ocean/atmosphere transfers (carbon, trace metals), but also on pelagic and benthic food resources (scallops, oysters, etc.). Phytoplankton composition has a direct impact on the entire ecosystem.

Objectives: In this context, we have identified several objectives common to the 3 LEMAR teams, including:

– study and better characterize the spatial and temporal distribution of phytoplankton and micro-phytobenthic populations

– assess the impact of biotic and abiotic factors on this spatial distribution

– study the biological and physiological responses of these phytoplanktonic and microphytobenthic populations to environmental forcings.

Around these themes, the objective of the transversal axis will therefore be:

(1) to share the knowledge and collaborations acquired individually by LEMAR researchers,

(2) to generate inter-team projects to better respond to the issues raised

(3) to better characterize our needs for advanced equipment and researchers specializing in the physiology and ecology of marine microbial communities.

Animation

Aude LEYNAERT (CNRS), Cécile KLEIN (UBO)

Organization

An effort of animation and training will be made within this transversal axis, in particular through the implementation of several actions.

1- bibliographic seminars: participants will meet regularly to present in a few minutes publications that are significant for the conceptual or technical progress they provide, or for the controversy they may generate.

2- Practical training on the laboratory’s instruments and culture facilities: a special effort will be made to train doctoral students in order to facilitate their autonomy on dedicated equipment.

3- Organisation of external training courses for the acquisition of new techniques and technologies concerning the problems developed.

4- Collective reflection on the needs for experimental and analytical structures (mesocosms, in situ measurements, community analysis, etc.).

5- Consultation and coordination on the purchase, installation and management of common equipment essential for experiments.

05/10/2018/by sherve@univ-brest.fr