SEM of Pseudo-nitzschia

Phytoplankton- What are they?


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.

Image of diatoms

..."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.

Harmful Algal Blooms (HABs) and Biotoxins

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.




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