Dynamic and functional response of benthic foraminifera and macrofauna in oyster farming area in the Pertuis Charentais

• Main Author: Bouchet, Vincent M.P.
• Other Authors: Bio-Indicateurs Actuels et Fossiles (BIAF), Université d'Angers (UA), Université d'Angers, Mr Jean-Pierre Debenay
• Format: Doctoral or Postdoctoral Thesis
• Language: French
• Published: HAL CCSD 2007
• Subjects: Oyster farming; intertidal areas; granulometry; organic matter; chlorophyl a; benthic macrofauna; benthic foraminifera; tolerant species; sensible species; macrofauna/foraminifera interactions; Ostréiculture; pertuis charentais; zone intertidale; granulométrie; matière organique; chlorophylle a; macrofaune benthique; foraminifères benthiques; espèces tolérantes; espèces sensibles; interaction macrofaune/foraminifères; bioturbation; CAT-scan; [SDU]Sciences of the Universe [physics]; Pacific; Crassostrea gigas
• Online Access: https://theses.hal.science/tel-00345844; https://theses.hal.science/tel-00345844v2/document; https://theses.hal.science/tel-00345844v2/file/Bouchet_2007_PhD.pdf

In oyster farming areas, organic matter fluxes toward sediment is increased. Pacific oysters (Crassostrea gigas) reject organic-rich faeces and pseudofaeces as a result of filtration process. Organic matter can be consumed by benthic fauna, but in excess it can entails the reduction of benthic faunal species richness, abundance and biomass. Organic matter degradation also induces hypoxic (or anoxic) conditions in the sediment, and production of ammonia and sulfides in toxic concentrations. The main objective of this study is to assess the effects of oyster farming on benthic intertidal ecosystems in the Pertuis Charentais. Benthic macrofauna, living (stained) foraminifera, and physicochemical characteristics of the water column and sediment were used as indicators to evaluate these effects. A multidisciplinary approach was conducted across the Pertuis Charentais at 3 different spatial scales: an oyster trestle (micro-scale), an oyster culture area (meso-scale) and various sites across the Pertuis Charentais (macro-scale). The study was also realised at 4 different temporal scales: some months for the spatial micro-scale, every two weeks for 2 years at meso-scale and once per season during one year at macro-scale. In this study, I found that oyster farming enriches sediment in fine particles, organic matter (up to 12 %), particulate organic carbon (15-20 μg mg-1) and leads to high microphytobenthic biomass. Moreover, the association of seasonnal warming (during spring and summer), remineralisation of accumulated organic matter and short-term hypoxic conditions leads to sulfides and ammonium production. Consequently, the benthic biodiversity decreases and the population dynamic is disturbed. The population dynamic disturbance is characterised by fast abundance rises followed by high mortality rates. In these conditions, tolerant benthic macrofaunal (Cirratulidae, Spionidae and Capitellidae) and foraminiferal (Ammonia tepida and Cribroelphidium gunteri) species are promoted. AMBI index confirms “medium” ecological ...