Suspended benthic microalgae in the water column reflect the strong benthic-pelagic coupling in coastal ecosystems and particularly in turbid macrotidal systems. Nevertheless, the temporal pattern of benthic microalgae contribution to phytoplankton assemblages has been largely overlooked, and yet it may provide significant clues for trophic studies, water quality assessment and understanding of toxic shellfish outbreaks related to phycotoxins produced by benthic species. The study, based on data acquired in a macrotidal system along the French Atlantic coast, analyze the seasonal contribution of benthic microalgal growth-forms to phytoplankton using a 12-year time-series from the Phytoplankton and Phycotoxin Monitoring Network (REPHY) implemented and managed by the French Research Institute for the Exploitation of the Sea (IFREMER). Here we provide all the information gathered in order to estimate microalgal biovolumes and carbon biomass. The table (.xls format) comprise four spreadsheet: i) a main table with all the information regarding the taxa-volume-carbon calculations, ii) equations for geometric forms, iii) a and b coefficients for the biovolume-to-carbon conversion and iv) all the references used.