Preprints
https://doi.org/10.5194/egusphere-2023-2782
https://doi.org/10.5194/egusphere-2023-2782
24 Nov 2023
 | 24 Nov 2023

Simulated terrestrial runoff shifts the metabolic balance of a coastal Mediterranean plankton community toward heterotrophy

Tanguy Soulié, Francesca Vidussi, Justine Courboulès, Marie Heydon, Sébastien Mas, Florian Voron, Carolina Cantoni, Fabien Joux, and Behzad Mostajir

Abstract. Climate change is projected to increase the frequency and intensity of extreme rainfall events in the Mediterranean region, increasing runoffs of terrestrial matter into coastal waters. To evaluate the consequences of terrestrial runoff on plankton key processes, an in situ mesocosm experiment was conducted for 18 days in the spring of 2021 in the coastal Mediterranean Thau Lagoon. Terrestrial runoff was simulated in replicate mesocosms by adding soil from an adjacent oak forest that had matured in water from the main river tributary of the lagoon. Automated high-frequency monitoring of dissolved oxygen, chlorophyll-a fluorescence, salinity, light, and temperature was combined with manual sampling of organic and inorganic nutrient pools, pH, carbonate chemistry and maximum quantum yield (Fv:Fm) of photosystem II (PSII). High-frequency data were used to estimate gross oxygen primary production (GPP), respiration (R), and phytoplankton growth (µ) and loss (L) rates. During the first half of the experiment (d2–d11), the simulated runoff reduced light availability (-52 %), chlorophyll-a concentrations (-70 %) and phytoplankton growth rates (-53 %). However, phytoplankton maintained a certain level of primary production by increasing its photosynthetic efficiency. Meanwhile, the runoff enhanced R (+53 %), shifting the metabolic status (GPP:R) of the system toward heterotrophy and increasing the partial pressure of carbon dioxide (pCO2), potentially switching the direction of the air-sea CO2 exchange. However, during the second part of the experiment (d11–d17), remineralised nutrients boosted phytoplankton growth (+299 %) in the terrestrial runoff treatment, but not its loss rates, leading to phytoplankton biomass accumulation and suggesting a mismatch between phytoplankton and its predators. Our study showed that a simulated terrestrial runoff significantly affected key plankton processes, suggesting that climate change-related increases in runoff frequency and intensity can shift the metabolic balance of Mediterranean coastal lagoons toward heterotrophy.

Tanguy Soulié, Francesca Vidussi, Justine Courboulès, Marie Heydon, Sébastien Mas, Florian Voron, Carolina Cantoni, Fabien Joux, and Behzad Mostajir

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • CC1: 'Comment on egusphere-2023-2782', A. Regaudie-de-Gioux, 30 Nov 2023
  • RC1: 'Comment on egusphere-2023-2782', Aurore Regaudie de Gioux, 01 Dec 2023
    • AC1: 'Reply on RC1', Tanguy Soulié, 14 Dec 2023
  • RC2: 'Comment on egusphere-2023-2782', Tamara Cibic, 04 Jan 2024
    • AC2: 'Reply on RC2', Tanguy Soulié, 17 Jan 2024

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • CC1: 'Comment on egusphere-2023-2782', A. Regaudie-de-Gioux, 30 Nov 2023
  • RC1: 'Comment on egusphere-2023-2782', Aurore Regaudie de Gioux, 01 Dec 2023
    • AC1: 'Reply on RC1', Tanguy Soulié, 14 Dec 2023
  • RC2: 'Comment on egusphere-2023-2782', Tamara Cibic, 04 Jan 2024
    • AC2: 'Reply on RC2', Tanguy Soulié, 17 Jan 2024
Tanguy Soulié, Francesca Vidussi, Justine Courboulès, Marie Heydon, Sébastien Mas, Florian Voron, Carolina Cantoni, Fabien Joux, and Behzad Mostajir

Data sets

Dataset from a mesocosm experiment testing the effects of a terrestrial runoff on a Mediterranean plankton community Soulié Tanguy, Vidussi Francesca, Courboulès Justine, Heydon Marie, Mas Sébastien, Voron Florian, Cantoni Carolina, Joux Fabien, Mostajir Behzad https://www.seanoe.org/data/00861/97260/

Tanguy Soulié, Francesca Vidussi, Justine Courboulès, Marie Heydon, Sébastien Mas, Florian Voron, Carolina Cantoni, Fabien Joux, and Behzad Mostajir

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Short summary
Due to climate change, it is projected that extreme rainfall events, bringing terrestrial matter into coastal seas, will occur more frequently in the Mediterranean region. To test the effects of runoffs of terrestrial matter on plankton communities from Mediterranean coastal waters, an in situ mesocosm experiment was conducted. The simulated runoff affected key processes mediated by plankton, such as primary production and respiration, suggesting major consequences of such events.