Alison Miserazzi’s research while affiliated with University of Bordeaux and other places

L’utilisation d’outils adaptés, efficaces et fiables est fondamentale pour mesurer et contrôler l’impact environnemental autour des installations industrielles. Robuste, autonome et permettant un suivi à distance et en ligne, la Valvométrie HFNI (Haute Fréquence Non Invasive) est une solution possible pour le biomonitoring des écosystèmes aquatiques. Elle permet l’étude à distance et en temps quasi-réel du comportement et de différents traits de vie de groupes de mollusques bivalves dans le milieu naturel par numérisation de leur activité valvaire. Les animaux sont ainsi utilisés comme des témoins représentatifs de la qualité de l’eau, capables de traduire la survenue d’évènements modifiant leur environnement. Détecter rapidement le début d’une perturbation et identifier sa nature sont des éléments clés du processus de réduction du risque environnemental. A ce titre, le premier objectif de cette thèse était d’analyser la capacité de réponse comportementale face à un pétrole brut de mollusques bivalves instrumentés avec la Valvométrie HFNI en situation multistress, représentative d’un contexte environnemental réaliste. Le second objectif était d’évaluer les perturbations sous-jacentes de leur milieu intérieur lors de l’exposition au pétrole brut et mieux comprendre le mécanisme des changements de comportement. Pour ce faire, des études ont été réalisées chez deux espèces de mollusques bivalves, la palourde d’eau douce Corbicula fluminea et l’huitre marine Magallana gigas, en conditions semi-naturelles ou contrôlées de laboratoire, avec des concentrations de pétrole brut constantes ou variables, environnementales (et dans un cas létales), et en présence de différents facteurs de stress additionnels : la température de l’eau, la turbidité, la présence de baryum, de pollution sonore ou d’hypoxie. La réponse comportementale au pétrole brut s’est avérée (i) claire et discernable dans la majorité des situations créées et (ii) fonction de la concentration, ce qui permet de proposer un schéma global d’évolution d’indices valvométriques dans la gamme 0 – 60 mg·L-1. Les perturbations du milieu intérieur ont été évaluées par une approche de protéomique sur des tissus en relation avec l’activité comportementale (branchies, muscles, ganglions nerveux). Quel que soit le tissu étudié, l’espèce ou les conditions d’exposition, les résultats traduisent une modification des processus métaboliques et cellulaires avec un impact toxicologique fonction de la contamination quantifiée par des dosages de HAP dans les tissus ou des valeurs nominales d’exposition. Ces analyses permettent d’aborder les bases explicatives du comportement chez les bivalves, de corréler comportement et changements du milieu intérieur et ouvrent la voie à des perspectives d’évaluation d’impacts en ligne et à distance.

The use of online remote control for 24/7 behavioural monitoring can play a key role in estimating the environmental status of aquatic ecosystems. Recording the valve activity of bivalve molluscs is a relevant approach in this context. However, a clear understanding of the underlying disturbances associated with behaviour is a key step. In this work, we studied freshwater Asian clams after exposure to crude oil (measured concentration, 167 ± 28 µg·L⁻¹) for three days in a semi-natural environment using outdoor artificial streams. Three complementary approaches to assess and explore disturbances were used: behaviour by high frequency non-invasive (HFNI) valvometry, tissue contamination with polycyclic aromatic hydrocarbons (PAH), and proteomic analysis. Two tissues were targeted: the pool adductor muscles – retractor pedal muscle – cerebral and visceral ganglia, which is the effector of any valve movement and the gills, which are on the frontline during contamination. The behavioural response was marked by an increase in valve closure-duration, a decrease in valve opening-amplitude and an increase in valve agitation index during opening periods. There was no significant PAH accumulation in the muscle plus nervous ganglia pool, contrary to the situation in the gills, although the latter remained in the low range of data available in literature. Major proteomic changes included (i) a slowdown in metabolic and/or cellular processes in muscles plus ganglia pool associated with minor toxicological effect and (ii) an increase of metabolic and/or cellular processes in gills associated with a greater toxicological effect. The nature of the proteomic changes is discussed in terms of unequal PAH distribution and allows to propose a set of explanatory mechanisms to associate behaviour to underlying physiological changes following oil exposure. First, the first tissues facing contaminated water are the inhalant siphon, the mantle edge and the gills. The routine nervous activity in the visceral ganglia should be modified by nervous information originating from these tissues. Second, the nervous activity in the visceral ganglia could be modified by its own specific contamination. Third, a decrease in nervous activity of the cerebral ganglia close to the mouth, including some kind of narcosis, could contribute to a decrease in visceral ganglia activity via a decrease or blockage of the downward neuromodulation by the cerebro-visceral connective. This whole set of events can explain the decrease of metabolic activity in the adductor muscles, contribute to initiate the catch mechanism and then deeply modify the valve behaviour.

Aquatic ecosystems are subject to many anthropogenic disturbances, and understanding their possible impacts is a real challenge. Developing approaches based on the behaviour of bivalve mollusks, an integrating marker of the state of the organisms, and therefore of their environment, is relevant, whether within a natural ecosystem or an ecosystem subject to industrial activities. The main objective of this study was to identify by HFNI Valvometry a reliable and reproducible clam behavioural response in the presence of crude oil in a multistress context. To closely replicate actual field conditions, Corbicula fluminea was exposed in outdoor artificial streams that were subject to natural variations and were continuously fed by fresh water from the Gave de Pau (S.W. France). After a period of 26 days in these artificial streams, the clams (n = 14-16 per condition) were separately exposed for 10 days to crude oil alone, crude oil and barium, crude oil and noise pollution, crude oil and turbidity pulses, barium alone, noise pollution alone, turbidity pulses alone or natural changes alone. The secondary objective was to characterize the accumulation of polycyclic aromatic hydrocarbons (PAH) in 3 tissues (gills, adductor muscles and foot) in clams exposed for 10 days to crude oil alone or under multistress conditions (n = 5 clams per condition) and then to compare the accumulation and behaviour of clams under these conditions. The response of clams to crude oil alone or under multistress conditions was visually and statistically significant and not confounded by the other disturbances tested, despite large variations in water temperature. In the presence of crude oil, the behaviour of clams was characterized by an increase in valve-closure duration, a decrease in valve-opening amplitude and an increase in valve agitation index. In the presence of crude oil, the clam behaviour showed no direct relationship with PAH accumulation in the gills, adductor muscles or foot, although hypothetical mechanisms are discussed. This work supports the growing interest in studying the behaviour of bivalve mollusks in the context of biomonitoring of the aquatic environment surrounding oil facilities.

Shipping has increased dramatically in recent decades and oysters can hear them. We studied the interaction between noise pollution and trace metal contamination in the oyster Magallana gigas. Four oyster-groups were studied during a 14-day exposure period. Two were exposed to cadmium in the presence of cargo ship-noise ([Cd⁺⁺]w ≈ 0.5 μg∙L⁻¹; maximum sound pressure level 150 dBrms re 1 μPa), and 2 were exposed only to cadmium. The Cd concentration in the gills ([Cd]g) and the digestive gland ([Cd]dg), the valve closure duration, number of valve closures and circadian distribution of opening and closure, the daily shell growth-rate and the expression of 19 genes in the gills were studied. Oysters exposed to Cd in the presence of cargo ship-noise accumulated 2.5 times less Cd in their gills than did the controls without ship noise and their growth rate was 2.6 times slower. In the presence of ship noise, oysters were closed more during the daytime, and their daily valve activity was reduced. Changes in gene activity in the gills were observed in 7 genes when the Cd was associated with the ship noise. In the absence of ship noise, a change in expression was measured in 4 genes. We conclude that chronic exposure to cargo ship noise has a depressant effect on the activity in oysters, including on the volume of the water flowing over their gills (Vw). In turn, a decrease in the Vw and valve-opening duration limited metal exposure and uptake by the gills but also limited food uptake. This latter conclusion would explain the slowing observed in the fat metabolism and growth rate. Thus, we propose that cargo ship noise exposure could protect against metal bioaccumulation and affect the growth rate. This latter conclusion points towards a potential risk in terms of ecosystem productivity.