This study presents a long-term monitoring dataset (2010–2023) from the Iroise Marine Natural Park, a French marine protected area in the NE Atlantic. It includes environmental parameters (temperature, salinity), microscopy-based phytoplankton counts, and zooplankton abundances and biovolumes estimated from imaging data. Two transects and three coastal stations were sampled seasonally, capturing spatial–temporal dynamics. This datasets offers new opportunities to study plankton diversity.