EFFECTS OF A MARINE HEATWAVE ON COASTAL ATLANTIC PLANKTON COMMUNITIES IN THE RÍA DE VIGO, NW SPAIN: A MESOCOSM EXPERIMENT WITH AUTOMATED SENSOR MEASUREMENTS

Marine heatwaves (HW), predicted to increase in frequency and intensity due to climate change, can significantly impact marine ecosystems, and notably plankton communities. A mesocosm experiment was performed to investigate the effects of a simulated HW on the metabolism and functioning of coastal plankton communities in the Ría de Vigo (NW Spain) during post-upwelling conditions (April-May 2023). Water temperature was raised by +3°C in triplicate HW mesocosms, compared to triplicate control mesocosms which followed natural temperature variations of the Ría. High-frequency (every minute) monitoring from automated sensors was used to estimate Gross Primary Production (GPP), community Respiration (R), phytoplankton growth (µ), and loss (L) rates. Daily manual sampling of the mesocosms enabled to monitor nutrient concentrations, phytoplankton community composition, size structure, and photosynthetic efficiency. The HW increased both GPP and R by 79% and 90%, respectively, without altering the metabolic index (GPP:R ratio). Phytoplankton µ was enhanced under HW conditions at the beginning of the experiment, shifting the trophic index (µ:L ratio) of the community toward biomass accumulation, while L increased during the second half. The HW enhanced photosynthetic efficiency, and shifted community and size structure, favoring prymnesiophytes over diatoms and dinoflagellates, key players in the Ría's ecosystem. Overall, the HW enhanced metabolic and trophic indexes, suggesting that Atlantic coastal upwelling systems may become biogeochemical hotspots under future HW conditions.

Presentation Preference: Oral

Primary Presenter: Tanguy Soulié, University of Montpellier-CNRS (tanguy.soulie@gmail.com)

Authors:

Tanguy Soulié, MARBEC (MARine Biodiversity, Exploitation, and Conservation), Univ Montpellier, CNRS, Ifremer, IRD, Montpellier, France  (tanguy.soulie@gmail.com)

Jose González, Centro de Investigación Mariña da Universidade de Vigo (CIM-UVIGO), Estación de Ciencias Mariñas de Toralla (ECIMAT), Vigo, Spain  (josegonzalez@uvigo.gal)

Pablo Serret, Centro de Investigación Mariña da Universidade de Vigo (CIM-UVIGO), Departamento de Ecoloxía e Bioloxía Animal, Vigo, Spain  (pserret@uvigo.gal)

Isabel Teixeira, Consejo Superior de Investigaciones Cientificas (CSIC), Instituto de Investigaciones Marinas, Vigo, Spain  (isabeltx@iim.csic.es)

Carmen González Castro, Consejo Superior de Investigaciones Cientificas (CSIC), Instituto de Investigaciones Marinas, Vigo, Spain  (cgcastro@iim.csic.es)

Sébastien Mas, MEDIMEER (MEDIterranean platform for Marine Ecosystems Experimental Research), OSU OREME, CNRS, Univ Montpellier, IRD, INRAE, Sète, France  (sebastien.mas1@umontpellier.fr)

David Parin, MEDIMEER (MEDIterranean platform for Marine Ecosystems Experimental Research), OSU OREME, CNRS, Univ Montpellier, IRD, INRAE, Sète, France  (david.parin@umontpellier.fr)

Francesca Vidussi, MARBEC (MARine Biodiversity, Exploitation, and Conservation), Univ Montpellier, CNRS, Ifremer, IRD, Montpellier, France  (Francesca.VIDUSSI@cnrs.fr)

Behzad Mostajir, MARBEC (MARine Biodiversity, Exploitation, and Conservation), Univ Montpellier, CNRS, Ifremer, IRD, Montpellier, France  (behzad.mostajir@umontpellier.fr)