Four common intertidal harpacticoid species (Paramphiascella fulvofasciata, Tigriopus brevicornis, Nitocra spinipes and Harpacticus obscurus) were offered pelagic diatoms (Phaeodactylum tricornutum) as food in laboratory experiments. To ensure generality we used copepod species originating from diverse habitats with different ecological characteristics. The diatoms were enriched in the stable carbon 13C isotope to facilitate tracing in the harpacticoids. Uptake of diatoms was clearly species-specific and in general P. fulvofasciata was more efficient than the other species. We found significant uptake by 24 h of incubation for T. brevicornis. From 24 h onwards we found an increase for all 3 species. Species had similar d13C values before and after starvation, indicating that labeled material was efficiently assimilated in their tissues. We tested whether diatom assimilation is density-dependent and this was true for 2 species (N. spinipes and P. fulvofasciata) but not for the semi-pelagic T. brevicornis. Finally, a positive effect of faecal pellets on food uptake for the less mobile species was shown, indicating that microbial gardening occurs within benthic harpacticoids as it does for several other crustacean species.