Marine Biology

FILTRATION

By this method, a known volume of water (10-100 ml/cm² of filter) is filtered through a membrane filter of 1µm porosity (vide section 5.3). The filter with the filtrate is dehydrated by passing through the concentrated ethanol stained with alcoholic fast green (0.1% in 95% ethanol) and finally washed with ethanol. The filter is then cleared with creosote; methoxy benzene (anisole) or immersion oil and mounted on a slide using Canada balsam, dissolved in toluene or xylol. For the cursory examination and counting of organisms, the memberane filter with the filtrate may be subjected to immersion oil and taken for Utermohl counting (vide section 5.3).

Though the preparation of good dehydrated and mounted slides is time consuming, it is advantageous as the prepared filters can be stored for a number of years.