Sampling, Biomass Estimation and Counts of Freshwater Algae - Freshwater Algae: Identification, Enumeration and Use as Bioindicators - page 74

Table 2.3 Species Counts and Biovolumes from the Lake Water Sample Shown in Fig. 2.16.

% Total Unit Species Total Species % Total

Count (Cells or Phytoplankton Biovolume Biovolume × 10 5 Phytoplankton

Species colonies ml −1 ) Count (μm 3 ) (μm 3 ml −1 ) Biovolume

Stephanodiscus minutula 12 000 78 380 46 13

Cryptomonas ovata 775 5 1050 8.1 2

Rhodomonas minuta 680 4 145 1.0 < 1

Anabaena flos-aquae∗ ∗ 120 1 2165 2.6 < 1

Synechococcus aeruginosa 30 < 1 20 0.005 < 1

Aphanizomenon flos-aquae∗ ∗ 480 3 1520 7.3 2

Ceratium hirundinella 30 < 1 40 000 12 4

Peridinium cinctum 578 4 48 000 280 77

Unit species biovolume: mean volume of a single cell or colony ( ∗ ), estimated from linear measurements; total species biovolume: volume
of the entire population of a single species, determined as the product of unit biovolume and cell count.
Percentage contributions: These are shown for each species in relation to total phytoplankton count and total phytoplankton biovolume
(shaded columns) and differ markedly in relation to unit (cell or colony) size.

Calculation of biovolumes

but often make a major contribution to phytoplank-
ton biomass.
Calculations of mean unit biovolumes for indi-
vidual species can be carried out from measured
dimensions of the organisms, treating them as simple
geometric shapes or as combinations of geometric
shapes. Some examples of standard cell shapes, key
dimensions, geometric formulae and representative
species are given in Fig. 2.17, and a list of typical
biovolumes for some common planktonic algae in
Table 2.4. A comprehensive reference set of geomet-
ric shapes and mathematical equations for calculating
biovolumes of

The biovolume of particular algal species within
mixed lake phytoplankton samples can be considered
in relation to
mean unit biovolume - the average volume of indi-
vidual organisms (cells or colonies), expressed as
μm 3
species population biovolume - the volume occu-
pied by single-species populations per unit volume
of lake water, expressed as μm 3 l −1 , and
total phytoplankton biovolume - the cumulative
volume occupied by all the species within the phy-
toplankton sample, expressed as μm 3 l −1

850 pelagic and benthic microalgae
from microscopic observations has been published
by Hillebrand et al . (1999).
Although typical unit biovolumes for particular
species based on geometric shapes can be obtained
from the literature (Bellinger, 1974; Reynolds and
Bellinger, 1992; Stephen, 1997), it is always prefer-
able to make calculations afresh for each phytoplank-
ton sample, preferably using live material. It should
be noted that variations in mean unit biovolume for a
particular species can vary spatially within a freshwa-
ter environment (e.g. lake water column), temporally
with season (Bellinger, 1977) and with conditions
of water quality - including heavy metal pollution
(Fig. 3.7) and acidity (see Section 3.2.3).

>

Mean unit biovolume Mean unit biovolume
depends on size and shape, which vary greatly from
species to species (Fig. 2.16). In some cases, algal
shape approximates to a simple three-dimensional
figure such as a sphere (e.g. Chlorella )orrod(e.g.
Melosira ) whilst others are more complicated ( Cer-
atium,Campylodiscus ). Calculation of mean unit bio-
volume for colonial algae such as Microcystis may
present particular problems, since they are typically
highly irregular in shape, vary considerably in size