Studies have documented a decrease in pelagic fish sizes in the Gulf of Lions (NW Mediterranean) over the last decade, leading to a crisis in fish catches. Most explanations for this change invoke a decline and/or change in phytoplankton production and diversity caused by decreasing nutrient inputs, increasing sea surface temperatures, or ocean acidification. As of yet, the changes affecting the phytoplankton community in the region remain relatively unconstrained. Here, we explore the use of deep-learning algorithms to study the changes in phytoplankton production and bloom dynamics in the Mediterranean Sea. We apply automated microscopy imaging to the record of nanno- and microplankton shells retrieved from a sediment trap series in the Gulf of Lions between 2010 and 2018. We use a machine learning-based workflow for calcareous nannoplankton classification to study the changes in species abundance, size, and calcification; we explore a novel workflow to study the siliceous microplankton record (diatoms, silicoflagellates). Our results show a decrease in overall coccolith production and mass over the interval of study, and a growing proportion of deep-dwelling species in the total coccolith assemblage. These results suggest increasing oligotrophic conditions in the Gulf of Lions which can, at this stage, be attributed to increasing column stratification in the region. We will compare these results to trends in siliceous plankton production, with the particular aim to describe the sequence of blooms in the region, and its alteration in the context of environmental change.

Primary Presenter: Camille Godbillot, Aix-Marseille Université (godbillot@cerege.fr)

Authors:

Camille Godbillot, Aix Marseille Univ, CNRS, IRD, INRAE, CEREGE, Aix-en-Provence, France  (godbillot@cerege.fr)

Luc Beaufort, Aix Marseille Univ, CNRS, IRD, INRAE, CEREGE, Aix-en-Provence, France  ()

Karine Leblanc, Aix Marseille Univ, Université de Toulon, CNRS, IRD, MIO, Marseille, France  ()

Julien Di Pane, Aix Marseille Univ, Université de Toulon, CNRS, IRD, MIO, Marseille, France  ()

Ross Marchant, Image Analytics, Benalla, Australia  ()

Yves Gally, Aix Marseille Univ, CNRS, IRD, INRAE, CEREGE, Aix-en-Provence, France  ()

Cristele Chevalier, Aix Marseille Univ, Université de Toulon, CNRS, IRD, MIO, Marseille, France  ()

Thang D. Q. Le, Aix Marseille Univ, Université de Toulon, CNRS, IRD, MIO, Marseille, France  ()

Baptiste Pesenti, Aix Marseille Univ, CNRS, IRD, INRAE, CEREGE, Aix-en-Provence, France  ()

Xavier Durrieu de Madron, Centre de Formation et de Recherche sur les Environnements Méditerranéens (CEFREM), CNRS/Université de Perpignan, Perpignan, France  ()

Thibault de Garidel-Thoron, Aix Marseille Univ, CNRS, IRD, INRAE, CEREGE, Aix-en-Provence, France  ()