1. The sedentary communities characteristic of float bottoms in Newport Harbor, California, are described.
2. The most important communities at present are dominated, respectively, by algae, bryozoans, Ciona intestinalis, Styela sp. and Mytilus sp.
3. These communities represent stages in an ecological succession.
4. The algal community appears first on freshly exposed surfaces, to be followed usually by a bryozoan community.
5. The bryozoans prominent in the bryozoan community settle more readily on surfaces supporting a vigorous growth of diatoms and other algae than on clean surfaces.
6. The community dominated by Mytilus constitutes the climax at present.
7. Mytilus has been observed to settle only on surfaces bearing a bryozoan, Ciona or Styela community.
8. The establishment of Ciona or Styela communities appears to depend in part on seasonal factors.
