Estimation of the biomass of plankton

Summary

A mathematical function is demonstrated in the numbers of individuals of the various species in a planktonic biocoenosis. The logarithms of the numbers form a Gauss or normal probability curve. A similar probability relation is found in the volumes of the individuals of the various species as well as in the biomass of the various populations.

This relationship in the numbers is caused by the effect of the numerous ecological factors influencing the rate of proliferation of the various plankton species. The cause of this relationship concerning the volumes of the various species is not understood. The relationship between the various biomasses is the mathematical product of number and mean volume.

An approximate hyperbolic function can be derived from the population volumes and with the aid of a simple equation the plankton biomass is calculated. A modus operandi is given to abbreviate the work necessary to determine the plankton biomass with Lohmann's method. Only ten or twenty of the most dominant populations out of all species present in a plankton sample, have to be counted and measured.

The biomasses of the populations in various plankton samples may easily be compared using the hyperbolic or the probability relationship.

The biomasses of plankton in various habitats may easily be compared in a graphic way. The logarithms of the biomasses found during the year follow a probability curve and may be plotted and compared on a cumulative logarithmic probability graph.

The number of organisms of each species to be counted depends on the degree of accuracy and has to be about a hundred. A chance determined spread is always found in plankton counts.

The spatial distribution of most plankters shows a very broad spread. Therefore, sampling at ten places and working with the mean of the ten samples is compulsory.

Some gregariously living zooplankters form bunches in the water. A reliable mean may be calculated using the hyperbolic function which seems to describe their densities at the various places.

From the existing methods of collection of plankton the rotary, electric pump is chosen. A translucent hose with a special and moving mouth is let down into the water. First the water passes through the plankton-net and after that through the pump and the water-meter. A series of 7 samples of increasing decimal volumes is drawn in this way. From these samples the plankton is concentrated and fractionated by means of two sedimentation chambers, four small plankton sieves and three plankton nets. The sieves and nets have various standardized meshes.

Square counting chambers of 10 cm² area are used. These chambers have a thin glass bottom and a broad rim. The sedimentation chambers and the small plankton sieves fit on and into the chambers thus minimizing the loss of organisms.

The plankton organisms are enumerated by means of an inverted microscope projecting the image on a ground glass which makes counting easier. Only those organisms seen within a measured square on the ground glass are counted.

By standardization of the sample volumes, the magnifications of the microscope and the dimensions of the squares the conversion factors are so simple that only zeros or a decimal point have to be placed in the number counted to obtain the result.

International standardization of the method of estimation of the biomass of plankton and the expression of the results is proposed.