QUANTITATIVE METHODS IN THE STUDY OF INTERSTITIAL FAUNA

Most work on interstitial microfauna has been done in the intertidal zone. More quantitative information on the subtidal is necessary. Some methods are proposed for sampling the undisturbed sea bottom by either ships or diving. For separation of the vagile interstitial fauna, especially ciliates and flagellates from the sediment, a simple method using seawater-ice is described. The animals are forced out of the sediment due to the high salinity of the melted seawater and the subsequent streaming action. In the last 40 years many papers have been published about the microfauna of marine sediments. New species and genera are continually being discovered and described; new families, orders, and even higher taxonomic groups are being created for interstitial specimens. However, the more descriptive details accumulated, the more necessary it becomes to do quantitative studies regarding distribution, abundance, migration, fluctuation, and other ecological relations. Furthermore, as most work has been done on the intertidal zone, it became apparent that more quantitative information on the subtidal area was necessary. Essentially, the limiting factors in studying interstitial fauna are the difficulties in the methodology which arise mainly from sampling, especially subtidally, as well as from separation and isolation methods. For quantitative studies it is very important to get undisturbed samples from the sea bottom. Furthermore, a factor often neglected is that flagellates, numer- ous small ciliates, and most acoel turbellarians are more or less "swimming- types." They possess few or no adhesive organelles for attachment. With stream- ing seawater through the sediment these animals may be passively displaced or lost. Therefore, the sediment sampler should not allow any outlet of interstitial water.