Factors Controlling the Localizations of Populations of Protodrilus symbioticus Giard

The environmental factors which might be expected to influence the distribution of intertidal interstitial animals are temperature, light, sand grain sizes, salinity variations, water-currents, oxygen tensions and the surfaces of the sand grains themselves. Boaden (1963) analysed in the laboratory the effect of light, salinity changes, water-currents and gregariousness on the distribution of Trilobodrilus heideri Remane. Boaden (1962) showed in field experiments how Protodrilus chaetifer Remane was limited to sands coarser than 500 [u whilst P. adhaerens Jagersten preferred sands with particles in the 210-105 ,u range. Wieser (1956) related the distribution of Cumella vulgaris Hart to sands with particles of 600-150 [Adiameter as only these could be manipulated by the mandibles when feeding. Later, Wieser (1959) showed that most interstitial species occurred in sands with particles greater than 200 u except for nematodes and active burrowers. In an attempt to analyse the factors influencing the localizations of populations of Protodrilus symbioticus on marine sandy beaches, the author has shown the influence on this species of temperature (Gray 1965), of light (Gray 1966a), of grain size (Gray 1966b), and of the surface films produced by bacteria on the sand grains themselves (Gray 1966c). The present paper deals with the effect of oxygen tension, salinity changes, and watercurrents on P. symbioticus. P. symbioticus was obtained from Black Rocks, Anglesey, and extracted from sand using the levitation method of Boisseau (Gray 1965). After each experiment the animals and substrate used were discarded.