Chapter Seventeen

Algae, including the beautiful Diatoms

17.1   Diatoms are a major group of algae, also within the phylum of Heterokonts and are among the most common types of phytoplankton. Diatoms are unicellular, although they can form colonies in the shape of filaments or ribbons (e.g. Fragilaria), fans (e.g. Meridion), zigzags (e.g. Tabellaria), or stars (e.g. Asterionella). The first diatom formally described in scientific literature, the colonial Bacillaria paradoxa, was found in 1783 by Danish naturalist Otto Friedrich Müller. Diatoms are producers within the food chain. A unique feature of diatom cells is that they are enclosed within a cell wall made of silica called a frustule. These frustules show a wide diversity in form, but are usually almost bilaterally symmetrical. The symmetry is not perfect since one of the valves is slightly larger than the other, allowing one valve to fit inside the edge of the other.

17.2   Diatom communities are a popular tool for monitoring environmental conditions, past and present, and are commonly used in studies of water quality. are a major group of algae, and are among the most common types of phytoplankton. A feature of diatoms is the urea cycle, which links them evolutionarily to animals. This was discovered in research carried out by Andrew Allen, Chris Bowler and colleagues. Their findings, published in 2011, that diatoms have a functioning urea cycle was highly significant, since prior to this, the urea cycle was thought to have originated with the metazoans who appeared several hundreds of millions of years after the diatoms. Their study showed that while diatoms and animals use the urea cycle for different ends, they are seen to be evolutionally linked in such a way that animals and plants are not.

17.3   Decomposition and decay of diatoms leads to organic and inorganic (in the form of silicates) sediment, the inorganic component of which can lead to a method of analyzing past marine environments by corings of ocean floors or bay muds, since the inorganic matter is embedded in deposition of clays and silts and forms a permanent geological record of such marine strata.

Diatom anatomy

17.5   The various sorts of algae play significant roles in aquatic ecology. Microscopic forms that live suspended in the water column (phytoplankton) provide the food base for most marine food chains. In very high densities (algal blooms) these algae may discolor the water and outcompete, poison, or asphyxiate other life forms.  That is exactly the danger that threatened Lake Annecy some sixty years ago, and was reason for the huge efforts made to build the sewage network around the lake.

17.6   Algae can be used as indicator organisms to monitor pollution in various aquatic systems. In many cases, algal metabolism is sensitive to various pollutants. Due to this, the species composition of algal populations may shift in the presence of chemical pollutants. To detect these changes, algae can be sampled from the environment and maintained in laboratories with relative ease.

17.7   Chrysophytes are a class within the phylum of Heterokonts. They contain the pigment fucoxanthin. Because of this, they were once considered to be a specialized form of cyanobacteria. Because many of these organisms had a silica capsule, they have a relatively complete fossil record, allowing modern biologists to confirm that they are, in fact, not derived from cyanobacteria, but rather an ancestor that did not possess the capability to photosynthesize. Many of the chrysophyta precursor fossils entirely lacked any type of photosynthesis-capable pigment. Most biologists believe that the chrysophytes obtained their ability to photosynthesize from an endosymbiotic relationship with fucoxanthin-containing cyanobacteria. Originally they were taken to include all such forms of the diatoms and multicellular brown algae, but since then they have been divided into several different groups based on pigmentation and cell structure.

17.8   The Chlorophyceae are one of the classes of green algae, in the division Chlorophyta within the kingdom Viridiplantae, defined by the arrangement of their flagella, which are displaced in a "clockwise" order.

Chrysophytes, or golden algae

Continue Reading   Chapter Eighteen