Plankton plays a key role in the bioconcentration and biomagnification of mercury (Hg) in marine food webs. Few studies have investigated the driving factors in coastal plankton food webs. Total-mercury (tHg) and total methylated-mercury (MeHg) were measured in seawater, size-fractioned phytoplankton (0.7 to 60 μm), zooplankton (60 to >2000 μm) and mysids, sampled monthly between February 2020 and November 2021 in the Bay of Marseille (NW Mediterranean Sea, France). Total-Hg and MeHg concentrati