The Vertical Distribution of the Infauna of a Sand Flat

This study is concerned with the vertical distribution of macroscopic invertebrates at two sites in Tomales Bay, California. Four sampling procedures were used to obtain data on more than 20,000 individuals. The infauna does not react to tidal fluctuations in water level by appreciable vertical movements in the areas studied. There is no evidence that the depth of the infauna varies with elevation in the range from 0 to 1 m above sea level. The average median depth of all species (except Phoronopsis harmeri) was found to be 8 cm in samples taken at low tide during daylight hours. Most species of the infauna and about 80% of the individuals occur in the upper 15 cm.