Contribution of imaging data to a trait-based approach arctic and subarctic copepod ecology

• Main Author: Vilgrain, Laure
• Other Authors: Laboratoire d'océanographie de Villefranche (LOV), Institut national des sciences de l'Univers (INSU - CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Institut de la Mer de Villefranche (IMEV), Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), Sorbonne Université, Université Laval (Québec, Canada), Sakina-Dorothée Ayata, Frédéric Maps
• Format: Doctoral or Postdoctoral Thesis
• Language: French
• Published: HAL CCSD 2023
• Subjects: Zooplankton; Arctic ecosystems; Imaging data; Numerical ecology; Functional traits; Copepods; Zooplancton; Écosystèmes arctiques; Imagerie; Écologie numérique; Traits fonctionnels; Copépodes; [SDU.STU.OC]Sciences of the Universe [physics]/Earth Sciences/Oceanography; Arctic; Arctique*; Sea ice; Subarctic; subarctique*
• Online Access: https://theses.hal.science/tel-04223081; https://theses.hal.science/tel-04223081/document; https://theses.hal.science/tel-04223081/file/VILGRAIN_Laure_these_2023.pdf

Copepods dominate the mesozooplankton biomass of arctic and sub-srctic regions, where light, ice and primary production are highly variable according to the season. By converting carbon fixed by microalgae into lipid reserves for winter survival, Calanus spp. are a crucial source of energy for fish, birds and marine mammals. Historically, copepod ecology was studied by taxonomic counting after net sampling. This thesis proposes another paradigm in the approach and tools for their study. A so-called "functional trait approach” is used to analyze properties that are measurable at the individual scale and influence the ecological success of organisms. Functional traits (i.e. size, trophic regime, vertical migration) are shared by several species and can be related to ecosystem functionalities such as carbon export, energy available for food webs, resilience, etc. Since a majority of the traits have a morphological signature, we defined them on two types of individual plankton images, that are complementary and commonly used: in situ Underwater Vision Profiler (UVP) images and color images taken during stereomicroscope observations. The objective of this thesis is to understand how functional traits of copepods, identified in images, can be related to environmental dynamics and functioning of arctic and sub-arctic ecosystems. In Chapter 1, we analyze in situ images taken by the UVP at the time of spring melt in the Canadian arctic. Morphological variables are used to project the images into a statistical space, and the axes synthesize morphological variation into three continuous features: size, opacity (which tells us about pigmented structures), and complexity of contour (likely indicating feeding activity through appendage visibility). This exploratory analysis revealed novel traits, having variations strongly correlated with sea ice melt and algal blooms phenology. Several arguments indicate that opacity maxima in individuals can be attributed to the presence of astaxanthin, a red carotenoid pigment. In Chapter ...