Seed banks can help to maintain the diversity of interacting phytoplankton species

•We model phytoplankton community dynamics including seed banks.•Empirically-motivated models are calibrated to observed phytoplankton time series.•Interactions between species include both competition and facilitation.•Removing seed banks leads to a drastic decrease in biodiversity.•Perturbations to intrinsic growth rates or interactions are buffered by seed banks.