Bioaccumulation and effects of mercury in cuttlefish in the context of ocean acidification

• Main Author: Minet, Antoine
• Other Authors: LIttoral ENvironnement et Sociétés (LIENSs), La Rochelle Université (ULR)-Centre National de la Recherche Scientifique (CNRS), Université de La Rochelle, Paco Bustamante, Christelle Jozet-Alves, Thomas Lacoue-Labarthe
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: HAL CCSD 2022
• Subjects: Cephalopod; IHg/MeHg; PH; Kinetics; Organotropism; Brain; Behavior; GABA; Céphalopode; Cinétique; Organotropisme; Cerveau; Comportement; [SDV.BA]Life Sciences [q-bio]/Animal biology; [SDV.SA]Life Sciences [q-bio]/Agricultural sciences; Ocean acidification
• Online Access: https://theses.hal.science/tel-04145265; https://theses.hal.science/tel-04145265/document; https://theses.hal.science/tel-04145265/file/2022Minet192409.pdf

The common cuttlefish, Sepia officinalis, is a coastal cephalopod known for its eco physiological performance supported by a wide repertoire of behaviors that allows it, despite its short life cycle, to play a central role in food webs. However, it is also known to efficiently accumulate metallic elements such as mercury (Hg), a neurotoxic contaminant in its organic form (methylmercury; MeHg). Moreover, in the context of global changes, ocean acidification (OA) induced by the increase of CO2 emissions, can impact metabolism, development and the central nervous system, especially in young life stages. The present work therefore aims to study the effects of OA on Hg bioaccumulation and the effects of these two neurotoxicants (Hg and CO2) on behavior and cognitive performance in juvenile cuttlefish. In the first place, in-situ measurements showed that Hg accumulated in the brain of cephalopods in methylated form (MeHg). Moreover, experimental approaches using isotopic tracers (stable and radioactive) of Hg have shown that the accumulation of total Hg comes mainly from the assimilation of MeHg present in preys, compared to the accumulation of inorganic mercury (iHg) dissolved in seawater. This MeHg is then very strongly retained despite evidence of Hg demethylation processes in the digestive gland. Surprisingly, OA has no effect on the bioaccumulation efficiencies and metabolism of Hg. In terms of effect, behavioral assays showed that Hg and CO2, alone or in combination, did not impact visual acuity and predation performance in juveniles. However, both induced an increase in locomotor activity, compromised defensive behavior through, in particular, an alteration of disruptive coloration and a non-alignment of lateralization. Among the neural processes likely to be impacted by Hg and CO2, the GABAergic system was analyzed in the optic lobes but showed no obvious link with behavioral responses suggesting more complex effect processes. All of this work therefore questions the effects of future ocean conditions on ...