The subject tackles the study of communities, food webs and the main oceanographic processes that take place in the ocean. We will present basic notions on the cycle of the organic matter in the marine environment. We will do special emphasis on microbial plankton communities, as they play a predominant role in marine biogeochemical cycles. The fundamental aim is to acquire basic knowledge on the communities of organisms, their interactions and the oceanographic processes in order to understand the role of the biology of the ocean in the Earth system functioning.