Distribution and Abundance of Interstitial Ciliates in Southampton Water in Relation to Physicochemical Conditions, Metal Pollution and the Availability of Food Organisms

Sediment samples were collected at low tide from eight sandy and muddy shores around Southampton Water on one occasion in July and one occasion in September. The temperature and pH of the sediments were measured at the time of collection, the water content of the sediments was determined and samples subjected to granulometric analysis. The population densities of bacteria and microflagellates were determined and the ciliates in sub-samples were identified to genus level and enumerated. The concentrations of cadmium, copper, lead, mercury and nickel in the interstitial water and in the dried sediments were measured by the dithizone and atomic absorption methods, respectively. These metal concentrations were compared with literature values for other British estuaries. Ciliates belonging to 23 genera were found in the sediments, the diversity of ciliates varying widely between stations. Bacterial numbers (mean 5×108 cm−3) at the various stations correlate with the surface area of the sediment particles and also correlate weakly with flagellate numbers (mean 2×104 cm−3). Total ciliate numbers (mean 1×103 cm−3) correlated quite strongly with flagellate numbers, but not with bacterial numbers.Euplotes,StrombidiumandUronemawere common at all stations and generally dominated;Didinium,Mesodinium pulexandPleuronemawere also found at all stations, and the latter two were often numerous;Uronychiawas found at seven stations. The distributions ofAcinetopsis,Blepharisma,Lacrymaria,M. pulex,Paramecium,Spirostomum,StrombidiumandVorticellashowed similar correlations to one another, and tended to favour sites nearer to sources of freshwater; these ciliates also showed a correlation with pH, river waters locally being alkaline. None of the ciliates showed correlations with any physical characteristics of the sediments. There were no negative correlations of ciliate distributions with metal pollutants. The levels of metal pollutants found in water drained from the sediments do not exceed concentrations to which laboratory cultures ofEuploteshave been found to acquire tolerance