Hanna-May MALAHEL

Coral-algal phase shift process in Guadeloupe: research of influencing factors and remediation tools

The Coral-algal phase shift (CAPS) is the transition from a coral-dominated community to one dominated by macroalgae. Eutrophication of the environment and reduced grazing pressure by herbivores are the main factors inducing this phenomenon. The degradation of the reef environment by various sources of pollution (soil erosion, fertilizer discharges from agriculture, inadequate wastewater treatment), coupled with the vulnerability of the reefs (bleaching, coral diseases), has led to the development and establishment of the CAPS phenomenon on Guadeloupe's reefs. The weight and influence of these different factors on the development of this disturbance are still poorly identified around the Guadeloupe archipelago.

The main objective of the thesis is to understand how the CAPS process works in the Guadeloupe reef context. The thesis will therefore lead to 1) an inventory of the factors influencing CAPS (location and monitoring of mineral pollution sources using an isotopic approach, algal community composition and spatio-temporal dynamics of their development, characterization of herbivore populations), 2) physiological monitoring of the absorption kinetics of nitrogenous molecules by macroalgae and zooxanthellae, 3) proposal of an active restoration method through herbivore repopulation experiments (in particular sea urchins Diadema antillarum and crabs Maguimithrax spinosissimus).