Diatoms



Looking like a small brown seaweed, this mass of plant material is really something quite different.  It is a colony of microscopic, single celled plants called diatoms that display a yellowish-brown color.  Diatoms occur as both colonies and as single cells.  You can find several types of colonies of diatoms: chains of round, tuna-can shaped individuals that form a large amorous mass (as seen in the photograph) or more organized branching filaments made up of numerous intertwined elongated individuals.  They are a common plant in marine and estuarine waters (as well as in fresh water) and are an important part of the marine food chain worldwide.


The small spheres in the yellow-brown mass in the photograph are bubbles of oxygen being produced by the plant on a sunny day.


Diatoms occur as single cells consisting of cellular material encased in overlapping shells of silica called a frustule or test.  They reproduce by vegetatively dividing the cell in two parts, each of which uses half of the old test. Since one half of the test is smaller than the other half, each successive generation is partly smaller than the original cell.  When a minimum size is reached, sexual reproduction occurs forming an auxospore which expands to a larger size.


According to Thomas Mumford, senior marine scientist with the Washington Department of Natural Resources, chain forming diatoms are common in the spring and fall when they will coat some sandy and muddy beaches - growing faster than they can be eaten.