william_dembowski's Journal

On April 20 I opened the book on a new iNaturalist project, “Diatoms and Desmids of the United States”, with the following general information:

About:
There is no more precious resource than an adequate supply of clean fresh water; and there is no better indicator of water purity than the micro-organisms which make it their home. The purpose of this project is to document the population of diatoms and desmids found in fresh surface waters of the United States and, when accompanied by additional data, to find a correlation between the pH value of those waters and the types of diatoms and desmids found there.

Terms:
Observations must be of freshwater diatoms and desmids of the United States; no marine varieties. Must be accompanied by micro-images suitable for identifying the organisms to the genus level. If possible, the pH value of the water sampled should be included to best serve the purposes of the project. Only images of living specimens will be used in the pH analysis but images of non-living specimens will also be accepted for use in general population studies.

I expanded the project to include all of the U.S. because relatively few people are equipped and/or motivated to participate in a project like this; and the larger area I cover, the more likely I am to attract participants. Of course, generating interest (even without participation) is not a bad thing.

(Project Update: Diatoms & Desmids of the U.S.A.)

Classifying micro-organisms can be a daunting task, especially since taxonomists themselves cannot agree on the system to be utilized. For example: the system used by iNaturalist places desmids in the Kingdom Plantae; another equally valid system places them in the Kingdom Proctista; and yet another in the Kingdom Chromista. From that point on, the matter only gets worse.

When researching micro-organisms on the internet one cannot always be certain which site is using which system and confusion of names can reign. One system might label a Family with a term that others do not recognize, or even use for another purpose. One minor saving grace is the photo-micrograph. If one cannot identify an organism by “name”, at least one can identify it by “sight”. Inadequate as it may sound, or actually be, this project will simply have to perform its work as best it can under the circumstances.

(Project Update: Diatoms & Desmids of the U.S.A.)

Diatoms are single celled golden algae that are encased in glass-like shells (frustules) composed mostly of silica that are intricately marked and nearly indestructible. Although they vary greatly in size, the most commonly encountered diatoms are from 10 to 200 microns long. A micron is 1/1000 of a millimeter.

There are more than 200 genera of living diatoms and approximately 100,000 extant species (plus many more fossil forms). Diatoms occur in virtually every environment that contains water. This includes not only oceans, seas, lakes, ponds and streams, but also soil. This project will deal only with the freshwater varieties.

Live diatoms contain chloroplasts which allow them to photosynthesize. These structures are typically shades of brown and yellow but other hues can occur. Non-living specimens lose their internal structures quite rapidly, leaving only the colorless frustule. In this state the finely etched patterns of the frustules can be plainly seen and are extremely useful in the identification process.

(Project Update: Diatoms & Desmids of the U.S.A.)

Diatoms are well established indicators of water purity and are particularly sensitive to the pH of the water in which they are found. It is said that the pH of a body of water can be inferred by identifying the diatoms which permanently reside there. One of the purposes of this project is to frequently monitor the population of diatoms in bodies of water to determine which are permanent residents and which are transients, either random or on a seasonal basis. Another purpose of the project is to find a correlation between the genera of diatoms found and the pH of their aquatic environment.

(Project Update: Diatoms & Desmids of the U.S.A.)

Desmids are an order of single celled green algae with approximately 40 genera and 6,000 species. They are divided into two compartments separated by a narrow bridge or isthmus. This gives them the appearance of being two cells, but they are actually a combination of two semi-cells sharing a single nucleus which lies in the isthmus between them. They range in size between 50 and 250 microns. A micron is 1/1000 of a millimeter.

Desmids are photosynthetic, and so it had been usual for taxonomists place them in the Kingdom Plantae. However, as more is learned about their internal chemistry, it is becoming more common to place them in the Kingdom Protista with all other forms of micro-algae. Contrary to “common knowledge”, algae are not true plants.

(Project Update: Diatoms & Desmids of the U.S.A.)

Desmids are dependent on clear, relatively nutrient-poor waters; and in many parts of the world they are a seriously threatened group of organisms. Most species only occur under a very specific combination of habitat variables. As such they may be considered excellent indicator organisms and are very useful in monitoring aquatic and semi-aquatic habitats.

Identifying and measuring all of the nutritional components of an aquatic eco-system is beyond the scope of this project. Instead, desmids will be documented on a “present / not-present” basis; with the eco-system thus being labeled as suitable or not suitable for their existence. The single most important indicator of unsuitability, in addition to the absence of desmids themselves, is the presence of large amounts of filamentous algae which flourish in nutrient-rich waters and rapidly crowd out the relatively “passive” desmid cells.

(Project Update: Diatoms & Desmids of the U.S.A.)

When taking a casual survey of the micro-organisms in a body of water, one or two observations of the same organism are sufficient. When making a serious population study, however, this is not the case. In a population study it is necessary to determine which organisms are permanent residents and which are transients. There are many variables that enter the study (temperature, pH, time of the year) that can influence changes in the population. That makes it necessary to document an organism every time it is encountered. I treat each lab session examining the same sample as a separate entity. I do not allow the results of yesterday’s session to influence what I record in today’s. One session typically consists of two or three slides, and I find that one sample will normally last for three days; after that it loses its vitality. A sample large enough to fill a ten gallon aquarium would probably have a longer shelf-life, but my usual sample is a pint or less.