Composition and Biomass of Phytoplankton
153
and sometimes seasonally among the same species under different growth conditions.
Cell volumes are calculated for each species by applying cellular dimensions to
formulae for solid geometric shapes most closely matching the shape of the cells.
Examples of geometric shapes are given in Fig. 10.10.
Other approaches for estimating biomass are to determine the concentration of a
particular chemical constituent of the phytoplankton per unit volume or per unit
surface area of water. The composite total may be reported without a breakdown
by species, such as total weight, or it may be reported as a concentration of an
algal-specific chemical constituent, such as photosynthetic pigments, carbon, or
nitrogen.
Organic Carbon of the Algae
The determination of total particulate organic carbon is discussed in Exercise 9.
Here again, no practical method exists to separate. particulate detritus from the
phytoplankton.
An estimate of organic carbon content of algae can be determined by the general
ratio of cellular carbon to cell volume. A ratio of cellular organic carbon (in }lg) to
cell volume (in }lm 3 II) of 0.10 has been found to be relatively constant for numerous
algae (Mullin et aI., 1966; Strathmann, 1967). This value, however, can be viewed as
no more than an approximate one [cf., Sicko-Goad et ai. (1977)]. An approximate
cell volume to cell carbon conversion is 0.2 pg CI}lm 3 for preserved nondiatom algal
species (0.1 pg CI}lm 3 for living flagellates) (Strathmann, 1967; Redalje and Laws,
1981; Borsheim and Bratbak, 1987). Cellular carbon often correlates better with
surface area than cell volume for diatoms (Strathmann, 1967; Bellinger, 1974).
Pigment Concentrations
Measurements of the concentration of photosynthetic pigments can be used to
estimate the composite biomass of phytoplanktonic populations. The methodology
for measuring pigments is relatively direct and accurate and can be performed both
on algae separated from the water as well as in vivo. Pigment concentrations of algae
can vary widely depending on metabolism, light, temperature, nutrient availability,
and many other factors. In addition, pigments of certain bacteria, especially those of
photosynthetic and nonphotosynthetic sulfur bacteria, can interfere with the analysis
of chlorophyll in algae. Chlorophyllous pigments also degrade to relatively stable
phaeophytin products, which interfere with the spectrophotometric or fluorometric
determinations of chlorophyll. Phaeophytin concentrations, however, can be
estimated separately on the same samples for which chlorophyll is determined. Thus,
pigment analyses can yield a sensitive approximation of algal biomass but, because
of physiological variability, interpretation of the data must be done with care.
Sample Preparation. Water samples should be filtered through either membrane or
glass fiber filters. The pore size of the filters must be sufficiently small to retain all
algae of the smallest dimensions. When membrane filters are used, a pore size of
0.45}lm (e.g., Millipore HA) is recommended; when glass fiber filters are employed,
a pore size of 0.5 to 0.7 }lm should be used (e.g., Reeve Angel 984H or Whatman
GFIF). The pressure differential during filtration should not exceed 0.3 atm, to
minimize damage to delicate organisms. The amount of sample required will vary
according to the concentration of phytoplankton. While 0.21 may be quite adequate
153
and sometimes seasonally among the same species under different growth conditions.
Cell volumes are calculated for each species by applying cellular dimensions to
formulae for solid geometric shapes most closely matching the shape of the cells.
Examples of geometric shapes are given in Fig. 10.10.
Other approaches for estimating biomass are to determine the concentration of a
particular chemical constituent of the phytoplankton per unit volume or per unit
surface area of water. The composite total may be reported without a breakdown
by species, such as total weight, or it may be reported as a concentration of an
algal-specific chemical constituent, such as photosynthetic pigments, carbon, or
nitrogen.
Organic Carbon of the Algae
The determination of total particulate organic carbon is discussed in Exercise 9.
Here again, no practical method exists to separate. particulate detritus from the
phytoplankton.
An estimate of organic carbon content of algae can be determined by the general
ratio of cellular carbon to cell volume. A ratio of cellular organic carbon (in }lg) to
cell volume (in }lm 3 II) of 0.10 has been found to be relatively constant for numerous
algae (Mullin et aI., 1966; Strathmann, 1967). This value, however, can be viewed as
no more than an approximate one [cf., Sicko-Goad et ai. (1977)]. An approximate
cell volume to cell carbon conversion is 0.2 pg CI}lm 3 for preserved nondiatom algal
species (0.1 pg CI}lm 3 for living flagellates) (Strathmann, 1967; Redalje and Laws,
1981; Borsheim and Bratbak, 1987). Cellular carbon often correlates better with
surface area than cell volume for diatoms (Strathmann, 1967; Bellinger, 1974).
Pigment Concentrations
Measurements of the concentration of photosynthetic pigments can be used to
estimate the composite biomass of phytoplanktonic populations. The methodology
for measuring pigments is relatively direct and accurate and can be performed both
on algae separated from the water as well as in vivo. Pigment concentrations of algae
can vary widely depending on metabolism, light, temperature, nutrient availability,
and many other factors. In addition, pigments of certain bacteria, especially those of
photosynthetic and nonphotosynthetic sulfur bacteria, can interfere with the analysis
of chlorophyll in algae. Chlorophyllous pigments also degrade to relatively stable
phaeophytin products, which interfere with the spectrophotometric or fluorometric
determinations of chlorophyll. Phaeophytin concentrations, however, can be
estimated separately on the same samples for which chlorophyll is determined. Thus,
pigment analyses can yield a sensitive approximation of algal biomass but, because
of physiological variability, interpretation of the data must be done with care.
Sample Preparation. Water samples should be filtered through either membrane or
glass fiber filters. The pore size of the filters must be sufficiently small to retain all
algae of the smallest dimensions. When membrane filters are used, a pore size of
0.45}lm (e.g., Millipore HA) is recommended; when glass fiber filters are employed,
a pore size of 0.5 to 0.7 }lm should be used (e.g., Reeve Angel 984H or Whatman
GFIF). The pressure differential during filtration should not exceed 0.3 atm, to
minimize damage to delicate organisms. The amount of sample required will vary
according to the concentration of phytoplankton. While 0.21 may be quite adequate