To assess the effects of 2 mangrove crabs on benthic meiofauna a laboratory experiment was performed in Zanzibar, eastern Africa. The 2 ocypodidae crab species Uca annulipes and Dotilla fenestrata are commonly found at mid to high water levels among Avicennia marina trees. Both genera are borrowers in soft sediments and feed upon drained surface deposits by forming pseudofaecal pellets. They are efficient bioturbers of the uppermost few mm of the sediment and some Uca species may prey directly on meiobenthos. The 2 species were added to microcosms containing sediment with natural meiofauna populations. After 10 d of enclosure, numbers of harpacticoid copepods in the top 1 cm layer were significantly lower in microcosms containing U. annulipes than in control microcosms. Two nematode assemblages were found in the microcosms, one in the surface layer and one deeper down. The crabs did not alter the structure of these assemblages. It appears that the nematodes are quite resilient to the reworking of the sediment surface. We conclude that the ocypodid crabs do not regulate resident nematode assemblages, but may inhibit settlement of colonisers that have not adapted to the intense surface disturbance created by these crabs. Such biological control is most likely to be in those areas where tidal water contains relatively high numbers of migrating meiofauna.