Dynamics of Symbiont Abundance in Bathymodiolin Deep-sea Symbioses

Deep-sea hydrothermal vents and cold seeps are widespread throughout the world's oceans and represent `oases of life' in a dark and hostile environment. These chemosynthetic habitats are often dominated by mussels of the genus Bathymodiolus. The bivalves harbor bacterial symbionts in their gills that use methane and reduced inorganic compounds such as sulfide and hydrogen as energy sources for chemosynthetic primary production. It is well known that the spatial and temporal gradients of these energy sources can be extremely steep at vents and seeps, and some studies have shown that differences in energy source availability affect symbiont abundance in Bathymodiolus mussels. However, in-depth analyses of physico-chemical gradients and their effect on symbiont abundance are lacking. One of the basic requirements for these analyses is a reliable quantification method for the symbionts. The goal of my thesis was therefore to develop an accurate and efficient protocol for determining symbiont abundance in bathymodiolin mussels.