Marine forests loss : causes and effects in the framework of their conservation and restoration

• Main Author: Monserrat Barcelo, Margalida
• Other Authors: Ecology and Conservation Science for Sustainable Seas (ECOSEAS), Centre National de la Recherche Scientifique (CNRS)-Université Côte d'Azur (UniCA), Université Côte d'Azur, Luisa Passeron-Mangialajo, Steeve Comeau
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: HAL CCSD 2023
• Subjects: Marine forests; Cystoseira compressa; Macroalgae communities; Ostreopsis; Benthic dinoflagellates; HABs; Ocean warming; Ocean acidification; Climate change; Regime shifts; Forêts marines; Communautés de macroalgues; Efflorescences algales nuisibles; Dinoflagellés benthiques; Réchauffement des océans; Acidification des océans; Changement climatique; Changement de régimes; [SDE.BE]Environmental Sciences/Biodiversity and Ecology; [SDU.STU.OC]Sciences of the Universe [physics]/Earth Sciences/Oceanography; [SDV.EE.BIO]Life Sciences [q-bio]/Ecology; environment/Bioclimatology
• Online Access: https://theses.hal.science/tel-04071065; https://theses.hal.science/tel-04071065/document; https://theses.hal.science/tel-04071065/file/2023COAZ4011.pdf

Large brown forest-forming macroalgae are dominant foundation species, ecosystem engineers of marine macroalgal forests. In the Mediterranean Sea, they are mainly represented by Cystoseira sensu lato spp. most of wich are endemic. They are also characterized for being long-lived species with short dispersal of the zygotes. Marine forests are one of the most productive and diverse ecosystems on earth. However, anthropogenic impacts are pushing them to the edge, causing regime shifts towards less complex communities such as shrubs, turfs, or even barren grounds. Marine forest loss affects the whole ecosystem, eventually making it more vulnerable to emergent phenomena such as benthic harmful algal blooms (BHAB). BHAB of the genus Ostreopsis spp. have been expanding in recent decades through temperate regions such as the Mediterranean Sea, where they have important public health, ecological and economic consequences. Major blooms are generally observed on macroalgal turfs and shrubs, suggesting that less structurally complex macroalgal communities could have an active role in promoting the proliferation of blooms.The main objectives of this thesis are (i) to assess some abiotic (climate change) and biotic (herbivory) causes of marine forests loss in the Mediterranean Sea and (ii) the potential consequences this loss can have in the context of BHABs proliferation. In the first two chapters, the causes of Cystoseira s.l. spp. loss were assessed. In Chapter 1, the effects of climate change and species facilitation on the recruitment of Cystoseira compressa were studied in controlled laboratory experiments. The major results from this chapter show that the interactive effects of ocean warming and acidification negatively affect C. compressa recruits, which are also negatively affected by the presence of crustose coralline algae. In Chapter 2 the grazing pressure and the effects of different invertebrates on recruits of C. compressa were assessed through field surveys and both field and laboratory-based experiments. The ...