HABs and Biotoxins: Phytoplankton
Marine algae come in a variety of sizes and forms. They range from large
sessile plants such as kelp to microscopic in single cells. The small, microscopic
plants are often referred to as microalgae or phytoplankton. Phytoplankton literally means 'phyto' = plant and 'planktos' = made to wander. Like terrestrial plants, these organisms
contain chlorophyll and need sunlight and inorganic nutrients to grow. Virtually
all marine phytoplankton are buoyant and live in the upper part of the water
column called the photic zone.
Most importantly, these marine marine microalgae or phytoplankton, similar to
terrestrial plants, use inorganic nutrients, such as nitrate, phosphates,
and sulfur, and convert them into the basic building blocks of living organisms--proteins,
fats, and carbohydrates. Like other living organisms, they also need trace
elements such as silicon, iron, and calcium.
..."Diatoms are so
exquisite it is hard to believe that they are also enormously
important. They are, one could argue, the most vital plants on
earth. They bob, drift, and sometimes glide through most of the
waters of the world in incredible numbers. Just one liter of sea
water may contain as many as 1 million of these one-celled specks
of algae- the primary foodstuff of the sea. Even land-dwelling
creatures, including man, are in their debt, for diatoms that
team in the upper few meters of the ocean produce, through photosynthesis,
much of the oxygen we breathe."
Richard B. Hoover in National Geographic
155(6):870, June 97
Two broad classes of phytoplankton that are of interest to researchers at the NWFSC
are dinoflagellates and diatoms.The dinoflagellates typically have a flagella
or whip-like tail that can move them through the water column. They are composed
of complex outer shells or armor plating (made of carbohydrate material) and
come in a variety of shapes and sizes.
Perhaps the most varied, beautiful and geometrically intricate of all the
phytoplankton are the diatoms (see the side bar to the right). Unlike most
phytoplankton, these organisms have a rigid silica shell (and require silicate
as an essential nutrient) composed of two interlocking parts. In contrast to
the dinoflagellates, diatoms do not propel themselves in the water column,
but are dependent on oceanic currents for transport. After diatoms die, their
silica shells are either solubilized back into the seawater or sink to
the bottom and eventually, given eons of time, become diatomaceous earth.
Phytoplankton, or algae, are normal components of all aquatic environments.
When they bloom in significant numbers (approximately 1 million cells per
liter of seawater equals a "bloom") and produce biotoxins, these events
are termed harmful algal blooms or HABs. These blooms can have deleterious
affects on both other aquatic life and on those who depend on that water for
subsistence. How and why these blooms occur is a complex issue, depending on oceanographic currents, winds, and other factors. To read more
about algal bloom dynamics, please use in the navigation bar to the right.
In the marine environment these HABs produce some of the most toxic compounds
known to man. In fact, the term Harmful Algal Blooms was initially coined
to describe high concentrations of algae that produce extremely potent poisons. During blooms, fish and
shellfish consume these algae, then accumulate and concentrate the biotoxins
without apparent harm. This renders the fish and shellfish extremely toxic
to whomever consumes them, including marine mammals, sea birds, and humans.
In places where HAB monitoring and surveillance programs do not exist, these
blooms may go unnoticed until they cause illnesses and/or death in humans
who consume products from the sea. The myriad of compounds, that marine phytoplankton can produce are known as marine biotoxins. For
more information about currently known marine biotoxins, please visit the
the navigation bar to the right.
HABs can also have less lethal effects that range from noxious odors and
aerosols to the production of slimes. In some circumstances,
due to coastal wind and wave action, algal blooms will produce components that can
be transported through the air, causing severe eye, nose, and throat irritation,
much akin to pollen and other plant constituents on land. Many of these
effects can have serious economic impacts on communities in coastal areas
that depend on marine resources for their livelihood. Here on the west coast, we are plagued
with several noxious HABs such as domoic acid, PSP, and Heterosigma fish poisoning.To read more about West coast HAB species, please use the navigation
bar to the right.