Beginning: December 2025
Supervisors: VANNIER Pauline, BURGAUD Gaëtan (Université de Bretagne Occidentale)
PLASDEEP Project
Marine plastic pollution has become a major global concern. In fact, nearly 30 million tons of plastic waste end up in the environment every year, with 3 to 10% of that ending up in the oceans. Once in the sea, plastic undergoes various physical and chemical degradation processes, including UV radiation, abrasion, and oxidation, fragmenting into microplastics (less than 5 mm in size). Under the effect of ocean currents, these plastics disperse from the surface to the deepest point in the oceans: the Mariana Trench, at a depth of 11 km. Once in the marine environment, these plastics are quickly colonized by microorganisms that form biofilms. These microbial communities on the surface of polymers are referred to as the plastisphere. Colonizing these polymer surfaces provides microorganisms with a relatively stable environment, enabling genetic exchanges and modifying the microbial loop of ecosystems. The structure and composition of the plastisphere vary depending on the nature of the polymer, its geographical location, and environmental factors. Some taxa have demonstrated their ability to degrade certain polymers. Most research on the plastisphere has focused on the first few meters of the water column, in the euphotic zone. Few studies have focused on the microbial communities of biofilms on polymer surfaces in the deep marine environment. However, the presence and accumulation of polymeric materials in the deep environment have been documented.
This thesis project aims to study the plastisphere of the deep sea, beyond 1,000 meters in depth, in environments that are subject to high hydrostatic pressures, low temperatures, and a total absence of sunlight. This project focuses on the bathypelagic zone, a vast region between 1,000 and 4,000 meters deep, which is the largest habitat on the planet.