An attempt has been made to deal briefly but quantitatively with all size groups of the fauna and flora in a marine mud deposit.
It has been necessary to propose the following new terminology: the Macrobenthos, which is here equivalent to the macrofauna, the Meiobenthos, under which term are included copepods, nematodes, foraminifera, etc., and the Microbenthos, comprising the rest of the protozoa, bacteria, bottom diatoms and other algae; planktonic diatoms and coloured flagellates also occur on the bottom in the region investigated but are not regarded as true microbenthos.
A quantitative ecological study of the microbenthos has been started and the habitat is first described, stress being laid on points of importance to the microorganisms.
The census method for bacteria was an agar-plate method and that for the protozoa and diatoms was a dilution culture method modified from that used by soil microbiologists.
These methods give minimal values for the total population and may safely be used for comparative purposes. The results are still tentative.
Typical figures for the minimal numbers and volumes of living protoplasm per gram of dry mud in the top ½ cm. layer are given in Tables I-IV.
The surface layer is much richer in all types of organisms than is the mud deeper in the cores. There is considerable local horizontal variation in numbers of bacteria and protozoa, suggesting dense aggregations.
Diatoms contribute by far the greatest bulk to the total volume of living micro-organisms; planktonic diatoms, particularly during the summer, completely outweigh the true microbenthos.
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