Effects of metals and climate changes on corals

• Main Author: Biscéré, Tom
• Other Authors: Ecologie marine tropicale des océans Pacifique et Indien (ENTROPIE Nouvelle-Calédonie ), Institut de Recherche pour le Développement (IRD Nouvelle-Calédonie )-Délégation Ifremer de Nouvelle-Calédonie, Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER)-Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER)-Université de la Nouvelle-Calédonie (UNC)-Centre National de la Recherche Scientifique (CNRS), Sorbonne Université, Fanny Houlbrèque, Claude-Elisabeth Payri
• Format: Doctoral or Postdoctoral Thesis
• Language: French
• Published: HAL CCSD 2018
• Subjects: Corals; Metals; Metallic trace elements; Climate change; New Caledonia; Coral Reefs; Coraux; Métaux; Éléments traces métalliques; Changements climatique; Nouvelle-Calédonie; Récifs coralliens; [SDV.TOX.ECO]Life Sciences [q-bio]/Toxicology/Ecotoxicology; [SDU.STU.OC]Sciences of the Universe [physics]/Earth Sciences/Oceanography; Ocean acidification
• Online Access: https://theses.hal.science/tel-02866069; https://theses.hal.science/tel-02866069/document; https://theses.hal.science/tel-02866069/file/these_BISCERE_Tom_2018.pdf

Coral reefs have largely degraded in recent decades under the influence of human activities. Among those disturbances, the increase in metal concentrations affects many reefs worldwide (e.g. Australian Great Barrier Reef, Costa Rica, Red Sea, New Caledonia). Furthermore, reefs have now to face climate change, and more particularly temperature increase and ocean acidification. In this context, the aims of my thesis were to (1) determine the effects of the main metals present in lateritic sediments (iron, manganese, nickel and cobalt) on coral physiology using concentrations representative of those measured along the New Caledonian coastline, and to (2) define their potential roles in this context of climate change. My results showed that metals affect coral metabolism in different ways. While at ambient temperature, a nickel or manganese enrichment stimulates host metabolism and symbiont photosynthesis, conversely a cobalt enrichment inhibits calcification and becomes even toxic for the host and symbionts, from 1 μg L-1. Despite its importance in photosynthetic processes, an iron enrichment induces a decrease in Symbiodinium densities and an inhibition of calcification rates. Under thermal stress, manganese enhances coral tolerance to temperature increase, likely by stimulating their antioxidant defenses, while nickel worsens its effects by decreasing even more their growth. These works represent an important step towards a better understanding of coral responses to metal enrichment and would explain, to some extent, species susceptibility to climate change. Les récifs coralliens se sont largement dégradés au cours de ces dernières décennies sous l’influence des activités anthropiques. Parmi ces perturbations, l’augmentation des concentrations métalliques concerne de nombreux récifs à travers le monde (e.g. grande barrière australienne, Costa Rica, Mer Rouge, Nouvelle-Calédonie). A ces stress locaux vient s’ajouter le changement climatique, et plus particulièrement l’élévation des températures et ...