Abundance of amoebae

  • Diffirential data on amoebae abundace allow us to calculate the real number of amoebae per square unit if the sediments. For this purpose we will use most evident, step-by-step extrapolation of amoebae numbers between subsamples. Below this algoritm is shown as a mathematical ratio, which is much more complicative than the algoritm really is.

  • Calculation gives us following results: depending on the site, sample, time of the year amoebae number varies from 9.2 mln to 69.7 mln per m2. In the upper layer of the bottom seiments their number reaches 600 ind./ml
  • How much is it. From this comparison we can see that in terms of ind/ml our data are average. Much more sufficient numbers were noted by researches. Even taking into account incompatibility of methods, differences of ectops and other possible factors we may safely conclude that abundnace of amoebae may reach several hundred specimens per ml of sediments.
  • Data in the terms of ind/square units are incomparable with any aviliable, as similar data were not obtained before this study. However, this allow us at least to evaluate number of amoebae comparing it with that of other groups of protists. For example, it is comparable with the number of ciliates in the similar benthic habitats (which normally consists about 50 mln ind/ml according to different data) or even exeeds them. Thus we should reserve to amoebae at least comparable role in freshwater benthos.

  • Following three curves illustrate number of species, the accumulation of fauna starting from the first sample in the core and the abundnace of amoebae in every sample. These are data on one typical core, results from other cores are similar in general patters. From the right side is the respective vertical profile of sediments in the core.

  • We may see, that both species diversity and abundance decrease with the increment of the depth. Really, only the layers consisting of detrit with gradually increasing content of ooze are inhabited with amoebae. However species diversity was exhausted only at the depth of 20 cm into the sediments. This, together with the data on three ecological groups of amoebae, shows us, that the usual samples of the "upper 3-4 mm layer" of the bottom sediemnts are far not enough to make any representative conclusion even on the biodiversity of amoebae in the sedeiments. Definitely, amoebae are most abundant in surface layers. However, usualy the maximum of abundace is situated not on the sediemnt surface, but below - at the depth 5 - 10 cm. I am not trying to explain this, but perhaps this point also should be noted when we are truing to calculate number of amoebae in the sediemnts from the data on surface samples.

  • Our diffirential quntitative data allows us to make one more interesting calculation. Here I tried to estimate the distribution of biovolumes of large, medium-sized and small amoebae in the sediments. For estimation of the cell volume I used the ration between cell volume and nuclear diameter, calculated by Rogerson and co-workers in 1994. The data show that in no case small amoebae represents the most of biovolume. This may be the results of overlooking of smallest amoebae (which is less probbale, as methods used in this study isolates small species even better than large and medium-sized) or (which is more probable) the result of the general specificity of freshwater amoebae fauna.
  • Generally, freshwater amoebae are larger than marine. There are much less small (below 25 microns) specis, then in marine habitats. Data on strong domination of small amoebae are obtained from the studies of marine plankton and benthos and it seems to be the specifity of marine ecotops. Anyway, in freshwater benthos medium sized species seems to dominate strongly from all points of view.

  • Following are the tables of primary data from the first 5 cores of sediements. Abundance in indicated in ind./ml (0.2 ml of sample was inoculated, thus all figures in the table are divisible to 5).

    Data from the core 1 (November 1993)

    Data from the core 2 (November, 1993)

    Data from the core 3 (May 1994)

    Data from the core 4 (July 1994)

    Data from the core 5 (July 1996)