Abstract Free-living marine nematode populations from a sheltered intertidal sandflat in a large sea lough in Northern Ireland were studied over a 12-month period. Analyses of the physical environment characterize the conditions found at the three sampling stations. High nematode densities were found throughout the year, with notable early summer maxima. Qualitative differences in species composition between the sampling sites are discussed. The assemblage is compared with the nematode fauna from similar habitats in other parts of the world.