There are millions of invisible life forms that are essential to life on earth. These microscopic organisms trap sun energy and kick start the entire marine food web. They are also responsible for the production of most of the earth’s oxygen. I am referring to the tiny diatoms and dinoflagellates that are collectively called the phytoplankton.
Dependent mostly on the waves and currents for their movement, the phytoplankton are floating microalgae that photosynthesize and initiate the transfer of energy from sunlight to living cells. Sometimes referred to as “plants of the sea” they are technically not true plants. Instead they belong to their own kingdom, the Protista and, along with the macroalgae or seaweeds, represent a significant ecological importance in the ocean.
The diatoms are the most abundant group of phytoplankton. They are single-celled and are constructed of two halves, an upper epitheca and a lower hypotheca. They divide frequently, about once every six days. While there is a great diversity of species of diatoms, most of them resemble one of two basic shapes: the cylindrical pennate forms and the circular centric forms. Diatoms are global environmental indicators, often used to study changes in climate and nutrient runoff from land. Because they need sunlight to photosynthesize they are restricted to the upper portions of the ocean surface where light can penetrate.
The dinoflagellates are another significant group of phytoplankton. These organisms also possess a pair of flagella which assist in movement. Occasionally they undergo a population explosion or bloom and this can create another problem, depending on the species. Alexandrium is a dinoflagellate in Cape waters that is responsible for red tide. Usually this occurs in the spring. Alexandrium contains a neurotoxin that becomes embedded in the tissues of filter-feeding animals such as mollusks. Humans that consume contaminated shellfish can become ill due to paralytic shellfish poisoning. Hence, these shellfish beds are closed until the numbers of plankton cells in the water column are substantially reduced and the mollusks, which are unaffected by the toxic plankton, can feed on other harmless species.
Copyright Gil Newton 2009 Thanks to Chris Dumas for logo image.