62
to the exponential phase, and excretion can be quite significant in pre
- as well as post - exponential phases, excretion must be expected to
have physiological and ecological significance in many cases. There
is ample evidence to indicate that changes in light, temperature, nutrient levels, salinity and population density may induce significant
excretion of organic compounds by otherwise "healthy" cells.
(Guillard and Wangersky, 1958; Marker, 1965; Soeder and Bolze, 1981).
The release of organic compounds py planktonic algae thus depends on
the physiological state of the cells as well as on many environmental
factors.
In addition,good evidence has been provided to show clear
differences between algal grQups and species. The diatom SI1.e1.e;toYlema
co~~ does not seem to excrete much organic carbon, even in the late
stationary phase, while several Chae;toceJUL6 species tend to release
large quantities of extracellular carbohydrate in this growth phase
(Myklestad and Haug, 1972; Myklestad, 1974, 1977). Dinoflagellates
seem to be good excretors in genereal (Marker, 1965; Wangersky, 1978).
Differences in behaviour between species may explain some of the disagreements found in the literature. Sharp (1977) based some of his
conclusions on results obtained with S. cMta.tum.
Other discrepancies
may have originated in the stress conditions unintentionally introduced
in the treatment of the algae. Among the stress factors which may influence excretion, nutrient deficiency is probably the most important.
EXCRETION AND NUTRIENTS
Nutrient levels and kinetics as well as excretion and release rates
are not easily studied in nature. The more conclusive information on
phytoplankton excretion has therefore been provided by studies of algal
cultures under defined conditions in the laboratory.
A wealth of organic compounds that may have come from algal sources
has been found in lake and seawater (for reviews see Duursma, 1965;
Collier, 1970; Wangersky, 1978), but only a limited numbers of compounds
are likely to be involved in excretion. Among these are glycol late
(Hellebust, 1965; Watt, 1969), glycerol (Graigie e~ ai., 1966), amino
acids and peptides (Fogg and Westlake, 1955; Hellebust, 1965; Aaronson
e~ ai., 1971; Walsby and Fogg, 1975) vitamin B 12 , thiamin and biotin
(Carlucci and Bowes, 1970; Aaronson e~ ai. 1971, and above all various
types of polysaccharides (Lewin, 1956; Marker, 1965; Hoyt, 1970; Aaronson, 1971; Huntsman, 1972; Myklestad and Haug, 1972; Myklestad e~ ai.,
1972, Myklestad, 1974, 1977). Excretion of toxins by dinoflagellates
to the exponential phase, and excretion can be quite significant in pre
- as well as post - exponential phases, excretion must be expected to
have physiological and ecological significance in many cases. There
is ample evidence to indicate that changes in light, temperature, nutrient levels, salinity and population density may induce significant
excretion of organic compounds by otherwise "healthy" cells.
(Guillard and Wangersky, 1958; Marker, 1965; Soeder and Bolze, 1981).
The release of organic compounds py planktonic algae thus depends on
the physiological state of the cells as well as on many environmental
factors.
In addition,good evidence has been provided to show clear
differences between algal grQups and species. The diatom SI1.e1.e;toYlema
co~~ does not seem to excrete much organic carbon, even in the late
stationary phase, while several Chae;toceJUL6 species tend to release
large quantities of extracellular carbohydrate in this growth phase
(Myklestad and Haug, 1972; Myklestad, 1974, 1977). Dinoflagellates
seem to be good excretors in genereal (Marker, 1965; Wangersky, 1978).
Differences in behaviour between species may explain some of the disagreements found in the literature. Sharp (1977) based some of his
conclusions on results obtained with S. cMta.tum.
Other discrepancies
may have originated in the stress conditions unintentionally introduced
in the treatment of the algae. Among the stress factors which may influence excretion, nutrient deficiency is probably the most important.
EXCRETION AND NUTRIENTS
Nutrient levels and kinetics as well as excretion and release rates
are not easily studied in nature. The more conclusive information on
phytoplankton excretion has therefore been provided by studies of algal
cultures under defined conditions in the laboratory.
A wealth of organic compounds that may have come from algal sources
has been found in lake and seawater (for reviews see Duursma, 1965;
Collier, 1970; Wangersky, 1978), but only a limited numbers of compounds
are likely to be involved in excretion. Among these are glycol late
(Hellebust, 1965; Watt, 1969), glycerol (Graigie e~ ai., 1966), amino
acids and peptides (Fogg and Westlake, 1955; Hellebust, 1965; Aaronson
e~ ai., 1971; Walsby and Fogg, 1975) vitamin B 12 , thiamin and biotin
(Carlucci and Bowes, 1970; Aaronson e~ ai. 1971, and above all various
types of polysaccharides (Lewin, 1956; Marker, 1965; Hoyt, 1970; Aaronson, 1971; Huntsman, 1972; Myklestad and Haug, 1972; Myklestad e~ ai.,
1972, Myklestad, 1974, 1977). Excretion of toxins by dinoflagellates