Insecticides and chalk, who would have thought! Interpreted as diatomaceous earth and coccoliths

Russell G. Rhodes

Department of Biology

Missouri State University

Springfield, Missouri


Algae play a significant role in our sphere.  We have the ability to utilize, control, and evaluate the algae.  As a group of organisms, we can simply refer to them as photosynthetic, although there are species that are both photosynthetic and heterotrophic, symbiotic, phagotrophic, and heterotrophic.  We can find algae that are very simple organisms consisting of single cells.  Some algae are colonial, others are filamentous and many are macroscopic and parenchymatous, somewhat similar to higher plants.  In addition include in general discussions of algae, organisms that are void of nuclei, chloroplasts and other organelles and grouped with the bacteria.  These organisms are called the cyanobacteria.  There are even algae that have characteristics that seem to blend characteristics of the bacteria and the eukaryotic algae.  These forms are only now becoming a recognized part of our sphere's biota.


Algae are found throughout our sphere from the atmosphere to ground water.  They occupy habitats that we prize such as prehistoric caves, and those that we wouldn't even thing of, such as rocks, ice, and hot springs.  We bring them into our homes and they can be found on carpet and on the sides of brick work, sidings, and roofs.  They even occupy our bird baths and give some of them a distinct red color on the bottom.


We have found a number of uses of algae that are of benefit.  Many of our common products such as toothpaste, asprin, insecticides, sushi, water filters, emulsifiers in salad dressing and other such products, to name a few are products of algae.  Before the "white board" there was the "chalk board" and the chalk was mined from formations like the White Cliffs of Dover which are accrual locations of coccoliths.

We can control algal growth as they have, when in abundance, undesirable effects such as green swimming pools, taste and odor effects on our drinking water, clarity of recreational water, and toxic products adversely affecting livestock, fish, dogs, and humans.


By understanding the properties associated with specific taxa of algae, we have the ability to qualitatively and quantitatively measure the algae in a variety of circumstances.  These measurements include species identification, and quantification, cellular chemical properties, and extracellular products from both living and dead algae.

Objectives of this presentation:

The objectives of this presentation include:

1.  Focusing on characteristics of taxa that have particular roles to play in our environment on this sphere

2.  Evaluating the  role that various taxa have in their habitats

3.  Determining what can be done for the control of some of the species that have particular adverse effects in their habitats.

Focus on Taxa

The algae are a very heterogenous group of organisms that range in size from 2 microns to 30 meters in length.  Some require planktonic nets with very small mesh size (20 microns) while others require ocean going barges to collect them.  The focus for this presentation is on the microscopic forms and not the macroscopic forms.  In both freshwater and marine habitats we can find macroscopic and microscopic forms and there the similarity ends.  Generally there are similar genera in both habitats, but species are generally specific to one or the other habitat.  Salinity has a controlling influence on the distribution of algae. 

There are three very significant terrestrial formations that contain an abundance of fossilized algae and these are used to provide examples of the extent of the algal preponderance and growth.  One of these are the deposits associated with diatomaceous earth, another is associated with chalk formations, and a third is associated with oil bearing shale.    We use these to illustrate that through time and analysis of core samples taken through earth accumulations, a variety of algae can be found and can be used to identify the kinds of habitats in which the fossils were thriving.

The focus in this presentation is on the former two examples of "algal deposits".   These examples include the taxa associated with diatoms, class Bacillariophyceae, and scaled and coccolith algae, class Chrysophyceae.  The third, while significant to our discussion, the classes Xanthophyceae and Chlorophyceae, is a topic of a future presentation.


Diatoms, while not the only group of organisms that have silicon as a skeletal feature, are the most abundant of those that do utilize silicon in their construction.  The silicon comprises the wall and is composed of two halves, one half fitting neatly inside the other, almost exactly like a petri plate.  Since silicon (glass) is a solid material when you drink from it, the diatom wall contains numerous holes, slots, and other orifices that permit gases, nutrients, minerals, and of course water to enter into the cytoplasm.  Imagine a glass that is lacey and try drinking from that.

The origin of the holes is through cytoplasmic formation of vesicles that originate from the golgi apparati of the cells.  As you can recall from cell biology, the golgi apparati get information from the nucleus and from DNA.  Hence the formation of these vesicles is dictated by the DNA, and that results in species specific orientation of the pores, slots, and other openings in the wall. 

To see these openings hereafter referred to as ornamentation, a misnomer but convenient, the cytoplasm must be removed.  There are several methods that are used to void the wall of organic material, and these include sulfuric acid, hydrogen peroxide, and incineration.  Of course this means that identification of diatoms is based on wall ornamentation.  This feature of the cell results in a taxonomic hierarchy of families that are grouped into two large groups.

Centric diatoms:  The general appearance of a centric diatom is one of a circle.  The wall is composed of two overlapping halves and the "circle" is the view of the valve.  Depending on the orientation of the cell it may appear as a rectangle and in that case the overlapping halves, the girdle halves, are seen and the valve is on edge.  The wall which is called the frustule does not have longitudinal slots and that is a universal feature of the centric diatoms.  Many of these species are planktonic.  Common genera include Coscinodiscus, Cyclotella, Melosira, and Stephanodiscus.  Not all centric diatoms have the appearance of a circular valve.  Some valves are more angular such as Biddulphia and Rhizosolenium.  Other taxa have extending seta from the valves and these are generally associated with marine forms, such as Skeletonema.  One interesting case that I worked on was the death of a set of fingerling trout in a hatchery.  I was sent prepared sections of the fingerlings and I asked for water samples.  In both I found Melosira with spines.  The Melosira were found in the gut and the fingerlings were reported to have "drowned".  My suggestion was that the spines penetrated the gut and allowed fluids to enter.

Centric diatoms may exist as individual cells, the whole organism.  Some of the cells remain attached valve to valve and form filaments as is the case with Melosira.

Coscinodiscus Coscinodiscus (phase) Ditylum (dividing) Melosira Stephanodiscus (division) Stephanodiscus (phase)

Pennate diatoms: The general appearance of pennate diatoms is one of variations of a boat with a hull shape of the Monitor.  Many of the pennate diatoms are unicellular but others may be either colonial or filamentous.   The frustule may be bilaterally symmetrical, symmetrical about an axis drawn through the two poles.  Other species may be bilaterally asymmetrical.  Others may be bilaterally symmetrical but asymmetrical about an axis drawn through the middle.  There are more technical terms but these descriptions will help in identification for now.

A new feature of some of the species of pennate diatoms is a raphe.  This feature is a slot through the silicon that allows cytoplasm and the membrane to have contact with a substrate and there is a resulting mobility of the diatom along the substrate.  Some species have a raphe on both valves and others have a raphe on only one valve.  For the most part pennate diatoms with raphes are benthic.  Some of the latter are epiphytic.  In the marine habitat, there are large colonies of "raphoid" diatoms that exist in the plankton.   Some species of raphoid diatoms exist as colonies in which cells are attached to stalks of a carbohydrate and protein combination.  One of the most interesting of this type is Didymosphenia.  This species has been found throughout the world and can be found in both Tennessee and Arkansas.

Other features of pennate diatoms include "shelves", ribs of silicon that extend into the cell.  Several genera that have these features are Diatoma and Rhoicosphenia.

Asterionella Fragilaria Gomphonema Navicula Epithemia Synedra
Amphipleura Nitzschia Cocconeis (raphe) Cocconeis (pseudoraphe) Meridion Fucoxanthin

Scaled and coccolith bearing Chrysophytes

There are other forms of algae that are unique in their coverings around the membrane and cytoplasm.  These coverings are commonly called scales and coccoliths.  These features are unique since they, too, originate from vesicles originating from the golgi apparatus and thus are guided in their formation presumably from DNA.  Thus the morphology of the scales and coccoliths are species specific.  Scales are composed of silica and coccoliths are composed of various kinds of calcium carbonate and both lend themselves to fossilization.  As with the diatoms there are both extinct and extant forms of these kinds of algae. 

Freshwater forms generally have scales, much smaller in size than the coccoliths which are generally associated with marine forms.  In fact one such coccolith bearing alga is known to have a very high photosynthetic contribution to the seas.  The freshwater forms have species that, if abundant in the phytoplankton, cause taste and odor problems for water treatment plant operators.  Examples of these are Synura and Mallomonas.

Synura Mallomonas Mallomonas (phase) Scaled picoflagellate



There is even another way in which algae have evolved cytoplasmic support.  This group of algae is known as the silicoflagellates.  In contrast to a frustule, as have the diatoms, the silicoflagellates have an internal piece of silicon and this skeleton is surrounded by the membrane and cytoplasm.  The cell also has two unequal length flagella and is typically found in estuaries.   There are two extant species, one heterotrophic (Ebria tripartita) and the second symbiotic with blue greens (Hermesinum adriatcum).  The fossil record is rich with silicoflagellaes.  The affinity of the two extant forms is close to the euglenoid flagellates.  I and Victoria Gibson found Hermesinum in the Chesapeake Bay and described the ecological settings of the organisms.

Hermesinum (endoskeleton) Hermesinum (with cytoplasm surrounding endoskeleton) Ebria (with cytoplasm surrounding endoskeleton)

Terrestrial Locations of Fossil Algae, Diatoms and Coccoliths

There was a time when some of the algae were in such abundance that they made, with their remains large deposits.  Such is the case with both diatoms and coccoliths.  One such deposit of diatoms is found in western US and another deposit of coccoliths is found in England.


References for Diatoms as Indicators  Excellent with images and list.  List of indicator diatoms  Centric to Pennate ratio as indicators of planktonic vs benthic habitats.  An excellent resource with biovolumes, and a large number of items related to diatoms. There is a section on paleolimnology also.  This is the main page for the above portion. An excellent resources  A resource for diatom images by genus. Excellent also.  Diatom microfossils, an excellent page  Diatom homepage Good article detailing using diatoms as indicators of eutrophication A very good article with figures and detailing using among other things diatoms as indicators of eutrophication Didymosphenia

References for Coccoliths  excellent photos  Calcareous nannofossils excellent images  towards bottom of site are links to excellent images of coccoliths used in stratigraphic dating.

References for Scaled Flagellates Silica scaled flagellates Beautiful images of Synura Mallomonas 

References for Silicoflagellates

Terrestrial Habitats  images of mines Images of abandoned mine  Really good image of mining for diatomaceous earth Mining diatomaceous earth in Kansas Excellent source for Chalk information