The Phytoplankton

In this course we will, of course, cover the autotrophs or phytoplankton, which is responsible for the genesis of approximately 70% of the world’s atmospheric oxygen. For these organisms to inhabit the open water, it is pertinent that they remain in the upper waters that have the highest light intensity (euphotic zone). However, since the euphotic zone is prone to turbulence (induced by wind, tide, etc.) remaining in the euphotic zone is an active process. It may be accomplished by many adaptive mechanisms alone or in combination, including flagellation, microscopic size (high surface area/volume, sinking increases with increased diameter), adaptive cell shape and reduced cell densities (lighter). Therefore the majority of organisms in the plankton are unicellular. The most prevalent in the marine phytoplankton are the dinoflagellates (10-80 μm) and the diatoms (20-100 μm). Morphological designs that deviate from the regular centric or spherical shape reduce sinking rates, which is especially obvious in the diatoms. Other unrelated algal groups such as the dinoflagellates and euglenoids have evolved lighter, “naked” or unarmored unicellular organisms, some of which are capable of shape changes.