Abstract's details
Ecological role of fine-scale ocean structures in structuring heterotrophic bacterioplankton communities: BioSWOT-Med campaign
Event: 2025 SWOT Science Team Meeting
Session: Oceanography: Regional Validation
Presentation type: Poster
Fine-scale oceanic structures (1–100 km), although short-lived (lasting from days to weeks), play a central role in marine chemical and biological dynamics. By generating intense horizontal gradients and associated vertical movements, they influence biogeochemical cycles and the structuring of planktonic biodiversity, even affecting the behavior of megafauna. However, these processes remain largely understudied in many oceanic regions, especially in oligotrophic and moderately energetic basins. The BioSWOT-Med campaign (https://doi.org/10.17600/18002392), conducted in spring 2023 in the area of the oligotrophic North Balearic Front (northwestern Mediterranean), forms part of the international effort to exploit data from the SWOT (Surface Water and Ocean Topography, NASA-CNES) mission, the first altimeter to provide two-dimensional sea surface observations at high spatio-temporal resolution.
The BioSWOT-Med campaign targeted three contrasting dynamic structures: a cyclonic recirculation in the north, an anticyclonic eddy in the south, and an eastward frontal jet separating them. An innovative, adaptive, and Lagrangian sampling strategy was implemented, combining several multi-disciplinary and high-frequency measurements. The collected data enabled a fine-scale characterization of the physical structure of water masses and their influence on the distribution of planktonic communities. While many studies have focused on phytoplankton, whose responses to physical ocean structuring are relatively well documented, heterotrophic bacterial communities (named “bacteria” hereafter) have long been understudied in such contexts, due to the challenges of taxonomic and functional identification without omics tools. Yet, bacteria play a key role in marine biogeochemical cycles, particularly in organic matter degradation, nutrient remineralization, and the regulation of carbon, nitrogen, phosphorus and iron cycles. Using flow cytometry to investigate the diversity and abundance of bacterial communities between 0 and 500 meters depth, alongside analyses of the physical and chemical characteristics of water masses, the study revealed changes in community composition and structure across the three oceanic features.
Functional statistical analyses showed that, interestingly, when comparing relative and absolute abundances, the front’s relative community structure appears intermediate between adjacent water masses, whereas its absolute abundances reveal a distinct pattern. This suggests that the front functions not only as a transitional zone, but also as a hotspot of bacterial accumulation or growth. Notably, this front is dominated by small-cell populations. The cyclonic recirculation is characterized by high variability and the presence of large-cell bacterial groups absent from the other structures. The southern anticyclonic eddy, by contrast, shows low variability due to its trapping nature and its low nutrient availability, and exhibits a deeper bacterioplanktonic signature throughout the water column. Finally, redundancy analysis indicates that a large part of the variance observed in bacterial community composition can be explained by the physico-chemical parameters measured (nutrients, fluorescence, temperature, salinity), highlighting the environmental structuring of these communities.
By integrating high-resolution coupled observations of physics, biogeochemistry, and biology, the BioSWOT-Med campaign demonstrates the potential of the SWOT satellite to link fine-scale ocean dynamics to biodiversity patterns. Conducted in a Mediterranean region representative of many global oligotrophic and low energetic systems, the campaign underscores the importance of integrating physical, biogeochemical, and biological dynamics to understand and model the functioning of marine ecosystems. These results provide a foundation for future global-scale research and emphasize the need for multi-scale and multi-disciplinary observations to understand the structuring of the oceanic biological landscape.
Back to the list of abstractThe BioSWOT-Med campaign targeted three contrasting dynamic structures: a cyclonic recirculation in the north, an anticyclonic eddy in the south, and an eastward frontal jet separating them. An innovative, adaptive, and Lagrangian sampling strategy was implemented, combining several multi-disciplinary and high-frequency measurements. The collected data enabled a fine-scale characterization of the physical structure of water masses and their influence on the distribution of planktonic communities. While many studies have focused on phytoplankton, whose responses to physical ocean structuring are relatively well documented, heterotrophic bacterial communities (named “bacteria” hereafter) have long been understudied in such contexts, due to the challenges of taxonomic and functional identification without omics tools. Yet, bacteria play a key role in marine biogeochemical cycles, particularly in organic matter degradation, nutrient remineralization, and the regulation of carbon, nitrogen, phosphorus and iron cycles. Using flow cytometry to investigate the diversity and abundance of bacterial communities between 0 and 500 meters depth, alongside analyses of the physical and chemical characteristics of water masses, the study revealed changes in community composition and structure across the three oceanic features.
Functional statistical analyses showed that, interestingly, when comparing relative and absolute abundances, the front’s relative community structure appears intermediate between adjacent water masses, whereas its absolute abundances reveal a distinct pattern. This suggests that the front functions not only as a transitional zone, but also as a hotspot of bacterial accumulation or growth. Notably, this front is dominated by small-cell populations. The cyclonic recirculation is characterized by high variability and the presence of large-cell bacterial groups absent from the other structures. The southern anticyclonic eddy, by contrast, shows low variability due to its trapping nature and its low nutrient availability, and exhibits a deeper bacterioplanktonic signature throughout the water column. Finally, redundancy analysis indicates that a large part of the variance observed in bacterial community composition can be explained by the physico-chemical parameters measured (nutrients, fluorescence, temperature, salinity), highlighting the environmental structuring of these communities.
By integrating high-resolution coupled observations of physics, biogeochemistry, and biology, the BioSWOT-Med campaign demonstrates the potential of the SWOT satellite to link fine-scale ocean dynamics to biodiversity patterns. Conducted in a Mediterranean region representative of many global oligotrophic and low energetic systems, the campaign underscores the importance of integrating physical, biogeochemical, and biological dynamics to understand and model the functioning of marine ecosystems. These results provide a foundation for future global-scale research and emphasize the need for multi-scale and multi-disciplinary observations to understand the structuring of the oceanic biological landscape.