What are Diatoms?

Diatoms can grow on moist land as well as in the water.
Diatoms can be found in the upper layers of the ocean.
A sample of sea water will have an array of diatoms that may be viewed under a microscope.
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  • Written By: Mary McMahon
  • Edited By: Bronwyn Harris
  • Last Modified Date: 31 August 2015
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Diatoms are unicellular algae which form distinct and beautiful cell walls from silica. They are widely distributed throughout the upper layers of the oceans of the world, and can also be found in fresh water or moist environments, such as the undersides of plants. There are over 16,000 recognized diatom species, with many more being constantly identified. Because diatoms are so plentiful, they form an important part of the pelagic food chain, serving as a food source for most of the animals in the ocean, either directly or indirectly.

Like many other algae species, diatoms photosynthesize their energy. They also have very limited mobility; some species of diatoms are capable of a slow oozing motion, but others rely on currents to carry them around the ocean. When they die, diatoms sink to the ocean bottom, contributing to the layer of sludge which makes up the sea floor. In parts of the world where oceans no longer exist, this sludge forms a fossilized layer of diatomaceous earth, a substance used in manufacturing and as a natural pesticide.


All diatoms belong to the class Bacillariophyta, although some biologists dispute over their precise classification. As a general rule, they are considered to be protists. They have a simple internal structure, and at some point in their life cycle, diatoms secrete silica to create strong cell walls. The cell walls take the form of two identical halves which interlock, much like the halves of a clam or mussel. The silica forms in a radially or bilaterally symmetric pattern, and it is often extremely complex and astounding to look at. Diatoms reproduce asexually, dividing themselves to create more diatoms.

In many cases, a diatom floats on its own through the ocean. In others, diatoms form huge colonies of individuals, linked together in a variety of ways. The unique organisms are sometimes called the jewels of the sea because of their distinctive cell walls. Many beginning biology students look at diatoms under the microscope to learn about the incredible detail which can be found in microscopic organisms. Any sample of sea water from the surface of a healthy ocean will contain a plethora of diatoms in an array of shapes to look at under a microscope.

Diatoms are similar to dinoflagellates, another large class of protists which inhabits the ocean. Dinoflagellates are more capable of motion than most diatoms, using flagellating arms to propel themselves. Some dinoflagellates also form symbiotic relationships with other organisms. Both were identified and described by early biologists, and numerous pamphlets demonstrating the powers of the microscope used drawings of these minute organisms as illustrations.


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Post 6

I'm trying to find out if it eats anything, or if something else eats it because I have to do a worksheet on it.

Post 5

Some fresh water diatoms are brown, but many ocean diatom blooms look light green. I have seen both, and I think that the oceanic diatom blooms are less disgusting.

I have a pond behind my house that sometimes gets lines of rusty brown scum on top during the spring and summer. I've been told that this is actually a diatom bloom, but I've always just called it algae or pond scum.

I have seen streaks and swirls of yellowish-green in the ocean. My brother-in-law is a marine biologist, and he informed me that these are diatom blooms. While not particularly attractive, they do look better than the brown pond scum.

Post 4

I had been having a lot of problems with brown algae in my aquarium. It was starting to cover the rocks, and a friend of mine told me that though it was called “algae,” it was actually a kind of diatom.

She had experienced the same problem in her tank. She told me that if I did not get rid of the brown diatoms, then they would turn into green algae.

She said that what I should try first is turning off my aquarium lights overnight. I didn't know this, but too much light could actually make the diatoms grow. She said I should only run the lights for about eight hours a day.

Turning off the lights took care of the problem. The brown diatoms were really disgusting to look at, and I'm glad I had her expertise to aid me.

Post 3

@OeKc05 – Diatomaceous earth is totally safe for you and your dogs. Be sure to buy the food grade, though, because it is the one that doesn't contain anything but diatoms. Other kinds might have chemicals added.

I have actually heard of people eating diatomaceous earth, because it is supposed to cleanse your colon. I've heard of farmers giving it to their animals, because it is supposed to get rid of parasites. They also sprinkle it wherever they store their grains to keep bugs from eating them.

The only thing that sounds bad about it is the way that it kills the bugs. It actually cuts into their bodies and zaps out their moisture, so they get sliced and dehydrated. I don't like to think about this.

Post 2

Has anyone here ever used diatomaceous earth as a pesticide? I've been considering putting it around my vegetables and fruit in my garden, but I want to make sure it is nontoxic first.

If my plants absorb it, will they still be safe to eat? Also, I have several dogs as pets. If they eat it, will it harm them?

I would love to give it a try, because it doesn't contain bad chemicals that could harm the environment. I just want to be sure it won't harm me or my dogs before I go dumping it on my food in an area to which the dogs have easy access.

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