Effects of a heatwave on the structure and composition of plankton food web components in a coastal zone of the Mediterranean Sea: a mesocosm study

Coastal lagoons are particularly affected by marine heat waves (HW) which impact the dynamics of plankton communities that are essential for the functioning and the productivity of ecosystems. To study the effect of a marine HW on plankton food web components, a mesocosm experiment was conducted in the Thau Lagoon (Mediterranean Sea, South of France) in May-June 2019. Two treatments were applied to six in situ mesocosms, each in triplicate. A HW of +3°C above the natural lagoon water temperature was applied to three mesocosms and maintained for the first 10 days of the experiment, after which heating was stopped and temperatures returned to natural levels for the remaining 10 days. The other three mesocosms followed the natural lagoon water temperature for the entire experiment. The simulated HW significantly reduced abundances of viruses, mixo- and heterotrophic flagellates, aloricate ciliates, picoeukaryotes, and diatoms (i. e. Cyclotella spp.). Conversely, cyanobacteria (i. e. Synechoccocus), autotrophic flagellates and pennate diatoms benefited from the HW. Stability parameters showed that diatoms, dinoflagellates, and ciliates exhibited low resistance and recovery but a high resilience. Conversely, inverse responses were observed for viruses, bacteria, and heterotrophic nanoflagellates. The contrasting resistance, resilience, and recovery of plankton functional groups to HW led to a restructuring of the plankton community. These changes may have repercussions within interactions of the food web and therefore could alter ecological functions of the pelagic ecosystem.

Presentation Preference: Oral

Primary Presenter: Zoe Eglaine, Montpellier University, CNRS, MARBEC (zoe.eglaine@gmail.com)

Authors:

Zoe Eglaine, MARBEC (Marine Biodiversity, Exploitation and Conservation), Univ Montpellier, CNRS, Ifremer, IRD, Montpellier, France  (zoe.eglaine@gmail.com)

Justine Courboulès, Norwegian University of science and Technology, NTNU  (courboules.justine@ntnu.no)

Francesco Cipolletta, Settore Biologia Levante, Agenzia Regionale per la Protezione dell’Ambiente Ligure, La Spezia, Italy  (francesco.cipolletta@arpal.liguria.it)

Cécile Roques, MARBEC (Marine Biodiversity, Exploitation and Conservation), Univ Montpellier, CNRS, Ifremer, IRD, Montpellier, France  (cecile.roques@cnrs.fr)

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

Diana Sarno, Department of Research Infrastructures for Marine Biological Resources, Stazione Zoologica Anton Dohrn, Naples, Italy  (diana.sarno@szn.it)

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

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