The word phytoplankton is used to include Blue-green Algae, Spirulina and Chlorella which are known foods for man as well as thousands more microalgae found in water on land and sea.
Blue-green Algae are more like bacteria and actually have been placed under the Phylum of Cyanobacteria.
Spirulina is blue-green and also falls under the Cyanobacteria Phylum. Spirulina are single celled, attaining sizes of 500 micrometers in length which makes some of these larger cells visible to the naked eye. All the Blue-green Algae lack a true nucleus; instead, the gene carrying material is dispersed throughout the cell. The chlorophyll pigment in Blue-green Algae are dispersed throughout the cell as well. They have a soft cell wall and are easily digested as a food by man. These algae food products come from lakes, ponds, and lagoons.
Chlorella are Green Algae and fall under the Phylum of Chlorophyta. It grows in ponds on land and very different from the Blue-green Algae in structure. Chlorella is considered a true plant form, having cell-walls of cellulose. Blue-green Algae do not.
A Chlorella cell is slightly larger than a red blood cell which is about 7 or 8 micrometers. It has a nucleus and chloroplasts contained, not dispersed. It's cell wall is not digestible by humans and has to be cracked open before marketed as a food.
One phytoplankton product we are eating comes from a sea farm off the coast of British Columbia, Canada. These plankton include many Phylum, including the Chlorophyta. The Chlorella do not grow in the ocean so is not a part of this Marine Phytoplankton.
Samples of the British Columbia coastal area have identified at least 200 known species between 1989 and 1996. They are single celled and vary in size from 10 to 200 micrometers. There is a website devoted to explaining more about the Marine Phytoplankton. Just go to Why Plankton Website
Janis Ihrig
More on Marine Phytoplankton at
http://www.arkadias-choice.com/plankton.php