Estuarine and Coastal Marine Science (1977) 5, 685-693 Ecology of Free-living Marine Nematodes from an Intertidal Sandflat in Strangford Lough, Northern Ireland Howard M. Platt The Queen’s University, Belfast, Northern Ireland” Received 19 December 1974 and in revised form 15 October 1976 Keywords: ecology, meiobenthos, intertidal sand habitat, Ireland coast, Nematoda Free-living marine nematode populations from a sheltered intertidal sandAat in a large sea lough in Northern Ireland were studied over a rz-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 cliffer- ences 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. Introduction Although free-living nematodes are the dominant meiofauna group in most benthic habitats, detailed studies of species from the British Isles have only recently been reported (Capstick, 1959; Gray & Rieger, 1971; Harris, 1972a, 1972b; McIntyre & Murison, 1973; Ward, 1973; Warwick, 1971; Warwick & Buchanan, 1970, 1971). Most recent work deals with exposed beaches or subtidal areas. From Ireland, data on marine nematodes are more scarce but Southern (1914) deals taxonomically with species from the west coast and Boaden (1968) and Boaden & Platt (1971) studied the vertical migration of the meiofauna from an exposed beach on the north-east coast. Boyd (1973a) recorded the presence of unidentified nematodes in plankton samples from Strangford Lough and considered them to be benthic forms. The work reported here contributes to the knowledge of the distribution of nematodes from sheltered intertidal environments in the British Isles. Data are presented on overall density, seasonal changes and species composition of the nematode populations. Species from the area which were new to science have been described in an earlier paper (Platt, 1973). The study area Strangford Lough is a large body of seawater extending 30 km from its narrow entrance in the south to its shallow upper reaches in the north (Figure I). The only freshwater influxes of any consequence are the Quoile Estuary in the south-west and the Comber River in the north-west. Neither have any great effect on the salinity of the Lough which varies little from that of the adjacent sea. Boyd (1973a) and Williams (1954) give detailed descriptions of the topography of the area, Williams (1954) provides a general fauna list for the Lough, while the meiofauna (other than nematodes) is reviewed by Boaden (1966). ‘Present address : British Antarctic Survey, Madingley Road, Cambridge CB3 oET, England 685