Biological invasions

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The ecological impacts of aquatic invasive species are a growing concern for coastal zone management and conservation. The French Channel-Atlantic coasts are no exception, mainly because of international shipping practices and aquaculture. France is even the European country most colonized by introduced species of macroalgae. The cost-benefit analysis of invasion management is not straightforward, even though the exploitation of several living resources is based on the invasive characteristics of these species (for example, molluscs and macrophytes in aquaculture). The oyster Crassostrea gigas is considered a nuisance species in the Wadden Sea or Australia, where it supplants native oysters, while it is the subject of a major exploitation in France at the same time. In addition, there are many historical cases showing that an invasion initially “under control” is not necessarily permanent, even after several decades. Understanding the interactions between human activities, the functioning of ecosystems and global change is therefore essential in order to establish new management options. New approaches need to be developed to prevent any inadvertent introduction and limit the side effects of ongoing invasions.

The impacts of the ongoing global changes are not conducive to optimism. Thus, the French Atlantic coast is confronted with at least three major environmental changes:

● the average annual temperature of seawater is rising steadily (about 1.5 ° C over the past 25 years),

● there is a very clear positive trend of the North Atlantic Oscillation (NAO),

● there is a drastic decrease in freshwater inputs due to climate change and concomitant changes in human activities on watersheds (eg increased irrigation for agriculture). The “marinating” of estuaries near ports leads to an increase in the potential risks of invasion by new marine species, while global warming favors the establishment of subtropical exotic species (for example the harmful dinoflagellates of the genera Ostreopsis and Gambierdiscus in the Bay of Biscay). By definition, species invaders are able to adapt to their new environment and are best placed to cope with global changes. What about native species that are not used to such environmental changes? Although climate change is progressive, will all species (native and invasive) adapt or will we observe a global homogenization of flora and fauna?

Retrospective approach to marine ecosystems

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The study of the structural and geochemical information archived in the carbonated structures of many marine organisms (bivalve shells, fish otoliths, rhodoliths, and hence the coccoliths) has undoubtedly been one of the points of interest for some fifteen years. strong and one of the specificities of LEMAR. This work highlights the considerable potential of these biogenic archives as witnesses to the current and past functioning of marine ecosystems. In recent years, LEMAR has focused on calibrating new proxies, including phytoplankton dynamics through bivalve shells (Li / Ca, Mo / Ca, Ba / Ca) or ocean acidification and climate change. with coccoliths (Li / Mg, B / Ca, δ11B), studies marked by the publication of pioneering articles in this field. It will be necessary to understand the biogeochemical mechanisms controlling the incorporation of certain tracers, and potentially new proxies, in these carbonated archives. This mechanistic approach will necessarily involve the implementation of experiments under controlled conditions (now made possible by the integration of Ifremer’s PFOM unit in 2012 and thanks to our methodological developments that make it possible to experimentally reproduce physicochemical forcings. under conditions that are representative of the natural environment), the establishment of a very high-frequency observatory of environmental conditions in Brest Bay, but also a modeling approach to the incorporation of trace elements and stable isotopes into these carbonated archives (eg DEB type models).

New methodologies for observing the coastal marine environment

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New methodologies for observing coastal marine environments are being developed. Among them is underwater acoustics and accelerometry, both at the individual level (ethology) and the community (ecology, observation, monitoring). This work already largely initiated in temperate environments (in Brest and Rimouski) in connection with the LIA BeBest and the partner INP Grenoble. Already conducted by the LEMAR in Brest, in the Iroise Sea, in the Arctic and in New Caledonia, research in this area has allowed us to study very precisely the metamorphosis, movements and energy that are associated, on benthic invertebrates under stressful, hypoxic, toxic or thermal stress situations. We have strong arguments that this approach, aimed at developing the use of new sensors, brings significant advances in marine ecology of subtidal environments. Passive acoustics offer the enormous advantage of being insensitive to the state of the sea and not being intrusive.

Impacts of environmental changes

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Coastal ecosystems are characterized by high natural variability at high frequency of the main abiotic factors.

Determining the possible reactions of living communities to anthropogenic pressures (chemical and plastic contamination, global warming, eutrophication, overexploitation of living resources) that generate proven global change is a real challenge for environmental scientists. In coastal marine environments where most of the ecological productivity is concentrated, the impact of chronic pollution raises additional questions for managers of these environments and producers of fish and aquaculture resources. Some alterations (genotoxicity, immunotoxicity, reprotoxicity) lead to population effects that may compromise the maintenance of certain species in the affected environments.

The number of coastal sites in the world ocean subjected to hypoxia and even anoxia events, more or less regularly and more or less pronounced, has increased dramatically since the 1950s. Most often, these phenomena are one of the consequences of the eutrophication of coastal areas, linked to the increasingly massive supply of nutrients to these waters. The latter stimulate phytoplankton production which, by sedimentation, induces a massive consumption of dissolved Oxygen at the water-sediment interface (bacterial degradation of this influx of organic matter). When the waters are stratified (e.g. during the summer), the bottom layer is isolated and is subjected to more or less prolonged hypoxic episodes, with serious consequences on benthic biocenoses.

Faced with various environmental pressures, marine organisms present adaptive responses of a behavioural, physiological (phenotypic plasticity), ontogenic and evolutionary nature that are individually reflected in their life traits and, at the individual and population level, in spatial-temporal dynamics.

Through a combination of experimental approaches (laboratory or in situ) and field observation studies, LEMAR will conduct several types of approaches including:

  • Mechanistic approach: characterize the adaptive responses of individuals from populations from contrasting sites in terms of exposure to chronic contamination.
  • Diagnostic approach: apply phenotypic descriptors corresponding to disturbances in essential physiological systems such as energy metabolism and the immune system, which are particularly important for the survival and development of populations.

Chemical ecology

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Coastal environments exhibit high diversity and high biomass in benthic organisms. The study of these organisms is of considerable importance at different levels, ie societal, economic and scientific. In these environments, marine organisms exhibit physiological adaptations to biotic and abiotic stresses, of natural and / or anthropogenic origin, producing original primary and / or secondary metabolites. These metabolites play a very important role in structuring the pelagic and benthic communities of these environments. Produced on the surface of organisms, these molecules can act on surface microorganisms. For those produced in the water column, such as allelopathic molecules for example, they are very active and often labile. The role of the microflora associated with these marine organisms in the production of defense molecules is also a subject of current interest and well-known interest. According to the prospective of chemical ecology published by the INEE, the studies in Chemical ecology participate at the same time to the knowledge resulting from the fundamental research, but also to the development of applications of this knowledge.