Effect of hydrodynamics on the structure of macroalgal communities and on the interactions between macroflora / macrofauna in the intertidal zone

• Main Author: Burel, Thomas
• Other Authors: Brest, Ar Gall, Erwan, Grall, Jacques, Schaal, Gauthier
• Format: Thesis
• Language: French
• Published: 2020
• Subjects: Macroalgues; Communautés; Estrans rocheux; Assemblages faune-flore; Hydrodynamisme; Macroalgae; Communities; Rocky shores; Fauna-flora Assemblages; Hydrodynamics; geo; envir; Western Head; North East Atlantic
• Online Access: http://www.theses.fr/2020BRES0019/document

This thesis aims at quantifying and explaining the effects of hydrodynamics on the communities of the North-East Atlantic rocky shores. In that prospect, several studies were carried out in 14 sites at the western head of Brittany, at different spatial scales, from a few metres to a hundred kilometres. Two biological sampling methods were used for macroflora and macrofauna to study variations in the structure of macroalgal communities and seaweed dominated assemblages. A new proxy for small-scale hydrodynamics has been developed, in situ wave height.In situ wave height appears to be the most important physical factor in the internal structuring of macroalgal communities. By studying the differentiation of six macroalgal communities vertically distributed on the shore, the role of hydrodynamics seems to be minor compared to the elevation and the average duration of emersion.The shift in intertidal dominance from macroflora to macrofauna is mainly explained by in situ wave height. Sessile organisms respond differently to hydrodynamics. Interestingly, the existence of tolerance thresholds for hydrodynamics was highlighted. Within the communities dominated by macroalgae, the in situ wave height significantly modulates both the fauna-flora interactions, strong at the top and middle of the shore, and the flora-flora interactions, more important at the bottom of the intertidal zone.Studying the effect of hydrodynamics on a midintertidal macroalgal community using seven proxies revealed different community responses. The wave heights measured in situ and calculated using theSWAN model appear to be complementary in assessing the role of hydrodynamics in the structuring of macroalgal-dominated rocky intertidal ecosystems. Cette thèse vise à quantifier et à expliciter les effets de l’hydrodynamisme sur les biocénoses des estrans rocheux du Nord-Est Atlantique. Dans cette optique, plusieurs études ont été menées sur 14 sites de la pointe bretonne, à différentes échelles spatiales, de quelques mètres à une centaine de ...