Marc Long
National
ANR JCJC AAPG2025
Start Date
14/03/2026
End Date
14/03/2026
Chemical communication is the most frequent mode of interaction in the living world. Although it is key to ecosystem functioning, our understanding of chemical interactions in plankton is limited. Nevertheless, some photosynthetic microorganisms can actively inhibit competitors by releasing compounds into the environment (interaction called “allelopathy”). Allelochemicals, the molecules that mediate these interactions, usually lead to the death and lysis of competitors. It gives an undeniable advantage to the allelopathic cells, but its effects at the population and community level are poorly investigated. Identifying the role of allelopathy in the ecology of microalgae is crucial, particularly for Harmful Algal Blooms (HAB), whose proliferation can be harmful to marine biota, human health and/or socio-economy.
The main objective of RASH-HAB is to assess the role of allelopathy in the ecology and dynamic of two allelopathic and HAB taxa: Alexandrium minutum and Pseudo-nitzschia australis. This project will explore a new hypothesis that could explain the sudden decline of some blooms: the allelopathic shuttle. Preliminary experiments performed since the last call validated this hypothesis: the release of sticky intracellular content following the allelopathic lysis can promote the formation of microalgal aggregates. Given the prominent role of “marine snow” (aggregates made of microalgae and organic detritus, debris) in the export of organic matter, the allelopathic shuttle might induce a significant export of cells to the benthic compartment. This newly-identified mechanism could trigger a modification of plankton community structure by inducing a sudden sink of microalgae, and by favouring the species remaining in surface. RASH-HAB will explore the allelopathic shuttle for the first time, and study its effects on the development of two HAB: either by favouring HAB species against competitors, or by favouring competing microalgae that could mitigate or suppress the development of HAB.
RASH-HAB is divided into 3 scientific work packages (WP) to ensure a balanced workload, an interactive feedback between results and to meet the scientific objectives. WP1’s goal is to study the ubiquity of allelopathic interactions within the interactions of the two HAB species. The proof of concept of and the study of the mechanisms of the allelopathic shuttle will be performed in WP2. In WP3, the allelopathic shuttle will be studied within natural communities by monitoring surface and settling plankton communities during blooms of allelopathic species.
RASH-HAB will significantly impact the field of HAB and plankton ecology. This project will significantly enhance our knowledge on the role of allelopathy in HAB ecology. By better describing the biotic parameters that control the development of HAB, it will improve the parametrization of HAB models. Therefore, helping to implement management strategies for mitigating HAB events by improving HAB forecast and early warning systems. This project will also have implications in the understanding of HAB effects as the allelopathic shuttle may result in toxic “marine snowfalls” with deleterious effects for the benthos. The scientific impact of RASH-HAB will not be limited to the plankton community, the allelopathic shuttle will also have implications for the understanding of energy fluxes and biogeochemical cycles in marine ecosystems. The allelopathic shuttle could significantly modify the fluxes of organic matter as this previously unidentified flux could contribute to vertical carbon export within the marine biological carbon pump (BPC).
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Laboratory Members
Contributors
Benjamin Bailleul (IBPC/ECOMAP)
