This project is following a previous IPEV project in 2017 (project 1166) and it is a part of the ANR project WAQMOS (2015-2020). The aims is to study, through a chronobiological approach, the clockwork of the Arctic scallop Chlamys islandica and as well the mussel Mytilus edulis, especially during the polar night. The scientific context of this project, supported by recent studies, is that polar night could be associated to a time of high biological activity in marine organisms, although the prevailing paradigm suggests the opposite situation with the presence of biological quiescence during polar night ,. We have already shown that the circadian rhythm of valve behavior is maintained even through the polar night. In the present project, we propose to study: a) Endogenous mechanisms underlying the circadian rhythm; b) Their synchronization by light intensity variations; c) the circannual rhythm. The molecular clockwork will be investigate in relationship with the valve behavior and the growth of bivalves. Finally, this study will be put into perspective to exacerbated global warming at the poles, which modify the life cycles between the bivalves and their food availability such as the phytoplankton.