Sellner
Kevin G.
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The global, complex phenomena of harmful algal blooms
Sellner
Kevin G.
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Marine and fresh waters team with life,
much of it microscopic, and most of it
harmless; in fact, it is this microscopic
life on which all aquatic life ultimately
depends for food. Microscopic algae
also play an important role in regulating
atmospheric CO2 by sequestering it
during production and transporting it
to deeper waters. Yet some of the microscopic
“algae” cause problems when they
accumulate in sufficient numbers, due
either to their production of endogenous
toxins, or to their sheer biomass or even
their physical shape. These are known as
the harmful algae, or, when in sufficient
numbers, harmful algal blooms (HABs).
These blooms were formerly called “red
tides” because many were composed of
dinoflagellates containing red pigments
that in high densities colored the water
red, but blooms may also be green, yellow,
or brown, depending on the type
of algae present and their pigmentation. As with all blooms, their proliferation results from a combination of
physical, chemical, and biological mechanisms
and their interactions with other
components of the food web that are for
the most part poorly understood. Most
HABs are dinoflagellates or cyanobacteria,
but other classes of algae, including
diatoms, have members that may form
HABs under some conditions. As stated
by J. Ryther and co-workers many years
ago, “...there is no necessity to postulate
obscure factors which would account for
a prodigious growth of dinoflagellates to
explain red water. It is necessary only to
have conditions favoring the growth and
dominance of a moderately large population
of a given species, and the proper
hydrographic and meteorological conditions
to permit the accumulation of organisms
at the surface and to effect their
future concentrations in localized areas”
(Ryther, 1955).