New insights into trophic ecology

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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.

Acoustic ecology

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Passive and active acoustics each contribute to the development of an acoustic ecology through different but non intrusive and non destructive methodologies. At the scale of aquatic ecosystems, active acoustics (sounder, sonar) allows the description of the “biotic landscape”, at high spatial and temporal resolutions, providing the distribution and density of nekton, micronekton and zooplankton present between the surface and the sea bed; fronts such as the thermocline or oxycline, can also be detected. Trophic relationships or physical/biological interactions can thus be highlighted. However, clarifying these remains a complex subject. Furthermore, for the intermediate trophic levels, biomass estimates, which are essential for many research projects (trophic environment of predators, hot spots to be preserved, contribution of nycthemeral migrations to carbon flows, improvement of biogeochemical or ecosystem models), require the recognition of organisms (gelatinous, crustaceans, mesopelagic fish), which remains a real challenge. Passive acoustics listens to and studies sounds from anthropophony (boats, threshing, fishing, etc.), from geophony (rain, waves, etc.) and from biophony. In invertebrates, passive acoustics is used in a wide range of applications, including the detection and identification of cryptic or endangered species, the estimation of population density, the location of individuals, and the monitoring of activity rhythms and the reproduction period. In the near future, passive acoustics should be able to offer new tools for assessing the health of marine ecosystems by combining biology, ecology, signal processing and artificial intelligence.

Functional ecology

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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.