A Drop of Water
I am fortunate to live just a couple of blocks from Golden Gate Park, the crown jewel of San Francisco. This park covers nearly 1,017 acres, draws 75,000 visitors each day and is dotted with about half a dozen lakes. One of my favorites is Stow Lake. Stow Lake offers paddle and row boats for rent, some great birding, beautiful stone bridges at several points around the lake that cross to an island in the center and a wonderful heron and egret rookery every Spring on another isolated island, along with assorted turtles and fish. When walking around the lake on the East side, one can see a beautiful waterfall and a Chinese outdoor pagoda and the only sounds to be heard are the waterfall and quiet conversations. But as you walk around the West side of the lake, busy 19th Avenue is only a couple of hundred feet away and the steady hum of traffic provides a kind of low-level white noise that underlies the sounds of Nature.
In spite of the traffic noise, this is my favorite side of the lake because it is where I get some of my best pond water for my microscope. Under a couple of bushes is a grate with quiet, still water and lots of indirect light, which is the perfect environment for many microscopic organisms. I bring along a little plastic bottle or an old jelly jar along with a pair of scissors to snip off some underwater vegetation and carefully collect assorted twigs and leaves that look promising along with the nasty looking water. Serious microscopists will examine the collection with a hand lens at the collection site, however, I like the element of chance. Besides, the micro-animals visible at the low powers of a hand lens (10-20x) are not what Im after any way. I like the invisible life that is teeming in these waters - ciliates, algae, diatoms, mastigotes, amoeba and bacteria.
After bringing my catch home, I add a little stale tap water (fresh tap water will kill most of these organisms) and place the jar in a corner of my lab (a pine door on concrete bricks). Its usually recommended to view your catch right away as some organisms will not live more than 24 hours outside of their native habitat, however, I am easily distracted and often dont get around to seeing what Ive caught until a couple of days or even a couple of weeks have gone by. I am never disappointed. A single drop of this water under the microscope at 60x is bursting with life. It often reminds me of cartoons I saw as a kid that showed city traffic from an aerial view with cars, trucks and people rushing in every direction. Its often too much at first but with a little careful scanning, one can usually find a quiet corner thats not so hectic and where its easier to raise the power to 120x and actually observe some detail.
One of the most common types of unicellular organisms are ciliates, usually oval or spherical in shape and covered in layers of tiny hairs (cilia) that help propel them and ingest food. The famous paramecium is one of the most studied organisms in biology and is often seen in pond water. Paramecium are often just visible to the naked eye, but the view through a microscope is stunning. They look like a large slipper and one can see hundreds of tiny cilia along the borders of this organism as well as large circular areas that appear and disappear. These circular areas are Water Expelling Vesicles (WEVs) that move water in and out of the cell to keep the organism in equilibrium with its environment. One of my favorite lighting techniques is dark field or dark ground lighting. I insert a small cardboard arrow into the filter holder of my microscope to block most of the light coming through the field of view and this lights up most organisms in a really unique way. The analogy is often made of sitting in a dark room with the curtains drawn and viewing dust particles in a shaft of light. Incredible detail can be seen with dark field lighting and the view is comparable to the view through a telescope of a star cluster - beautiful little jewels spread on black velvet. The view through a telescope is more user-friendly in that stars are not moving around looking for a meal or trying to avoid being eaten. However, when Im at my microscope, Im always nice and warm and I dont need to wait for a clear night to observe.
Another common denizen of pond water is the mastigote, or flagellate. Some scientists, both professional and amateur, avoid the term flagellate, however, it is still commonly used by many microscopists (just as protozoa is still in use even though it is scientifically outdated). Protozoa means first animal and when I was in grade school, protists were usually placed in the animal kingdom. However, there are now currently five accepted domains - Bacteria, Protists, Fungi, Animals and Plants and so all of the unicellular organisms fall under the domain Protista. So, too, the flagellates were originally named because of the flagella or whip that protrudes from the front and/or rear that are rotated rapidly to both propel the organism through water and draw in food for sustenance. Some scientists now hold the view that only bacteria have true flagella and the protists with whips should be called Mastigotes and their whips should be called undulipodia rather than flagella. Believe it or not, professional scientists can get really worked up over these differences (one book I read said they nearly came to blows over the matter), however, amateur scientists such as myself can take a more relaxed view. Regardless of how you name them, these are amazing creatures and a wonder to behold. Again, the dark field view is usually more rewarding as the undulipodia or flagella are often less then a micron in width. A micron is 1,000th of a millimeter, approximately 0.0005118 inches. The wave length of light is roughly one quarter to one half a micron, so the little whips are just visible under a light microscope. The cell shapes range from spherical to elongated and mastigotes generally much smaller than ciliates, however, they often move slower so are easier to observe . One of my favorites is one that I never identified, but it has two undulipodia protruding at 45 degree angles from the anterior or frontal position, each of them rotating so fast that they form little loops. It always reminds me of a microscopic cowboy doing really fancy lasso tricks with a rope. Another great mastigote is Euglena, which often forms green pond scum in early Spring. This is an oblong shaped organism with one long undulipodia at sticking straight out propelling it through the water while the body morphs into incredible shapes. I saw one recently going through amazing morphs, at one time even turning itself into a mushroom shape
Another common pond water organism is the amoeba. Many amoebas build little shells, also called tests, and so dont look like the typical blob that you think of when you think of an amoeba. But there are plenty of blob-type amoebas in any kind of pond water. The trick to viewing them is lots of patience. They move so slowly that you usually have to watch for several minutes before seeing them morph from one shape to another. These amazing creatures create pseudopods, or feet, at will, to walk around the microscope slide, looking for their next meal. I mentioned above how I really love the dark field view through a microscope, but using dark field, its almost impossible to spot these types of amoebas. There is another lighting trick called oblique lighting and to use this I pivot my little arrow to block only part of the light coming through the microscope. This creates a 3-D effect that makes it much easier to spot these elusive creatures, but it still requires a patient eye to find them. Once youve spotted them, there is no doubt that what youre seeing is alive and moving and really amazing. No head, no brain, no arms, no legs - just feet and protoplasm and totally bizarre. I mentioned the shelled amoebas above. Many of these are in a group called Heliozoa which means sun animals. They are called Sun animalcules because they are little spheres with numerous spikes protruding from the shell in every direction making them look like little suns with rays sticking out. These are very easy to spot with either dark field or oblique lighting, however, more often than not, there is no movement detectable no matter how long I look. The spikes are actually incredibly tiny poison needles that pierce their prey. After an unsuspecting protist is impaled on a spike, the needle turns into a straw to suck the essence out of the prey and feed the amoeba. Pretty weird!
And then there are the diatoms. These are little protists that usually look like little submarines tooling around the slide. They use silicate to create a glass-like shell. The White Cliffs of Dover consist of countless millions of diatom shells. They best time to see these little guys moving around is within 24 to 48 hours of collecting them. They move quite slowly but the movement is enough to easily spot and because of the slow movement, they are quite easy to observe. Diatoms look great under both dark field and oblique lighting.
This is just a very rough overview of the major groups of protists seen in pond water under a microscope. I have a few photos posted on my web site at http://virtualcolony.com/micro/ which show some of the organisms Ive mentioned and a few that I havent. In a later post, I will describe some of the micro-animals commonly found in pond water such as rotifers, nematodes, gastrotrichs and tardigrades, also called water bears.
The views through a telescope of Saturn, the Moon and the bright deep sky objects are always beautiful and amazing, but the views of pond water life through a microscope are equally stunning and fascinating. Ive thought many times that the people who create special effects for films would be greatly inspired by what I see under the microscope because many pond water organisms are way more bizarre then a giant bug or some green guy with scales and tentacles.
But the most amazing thing about my little drop of pond water from Stow Lake is when I think about the fact that Im looking at hundreds of organisms in one little corner of one little drop that came from a lake with hundreds of thousands of gallons of water. When I think of all the lakes in Golden Gate Park alone, never mind the rest of the world, the amount of life that is there is staggering. The numbers are so great that it is somewhat like Quantum Mechanics if you think you understand it, then you really dont get it.
To see some great photography of protozoa, click on the Microscopy 101 link to the left or visit Droplet.Sidewalk Astronomer