There is an invisible basis for the wildlife and plants that we all enjoy in our city parks in Edmonds. The hoard of microorganisms are generally not at all obvious, but like other very tiny living things such as cholera or plague bacteria, they can have a very large impact. In this case, the impact is mostly beneficial. We were curious about this world, about which few are aware, but which form a basis for the food web of any ecosystem. While a few species have, from our point of view, negative effects (algal blooms, bacterial infections and poisoning of shell fish) the vast majority of these microscopic organisms are necessary to the functioning of our ecosystems, and in fact have major impacts on our lives. Among these are bacteria, protists, and a few microscopic or near microscopic multicellular organisms like flat worms and rotifers. Without these organisms we would lack fish, whales, porpoises, Orcas, birds and just about every large creature, and be lacking in both carbon storage and breathable oxygen.
To examine this invisible world we decided to sample selected aquatic systems in several city parks, using a mosquito larva dipper and a plankton net (the latter for sampling Puget Sound off the Fishing Pier.) Beside the salt water Fishing Pier site, we sampled freshwater systems in Pine Ridge Park (Goodhope Pond), Edmonds Marsh, and Willow Creek. A few preliminary samples were made and the exact final sites selected for two snapshot samples in mid-May and late June of this year. We both used binocular compound microscopes with attached electronic cameras to take photos of the living things we found. Both of us took part of each sample and examined them separately. The list of microorganisms did not include bacteria (except some of the larger cyanobacteria), which are beyond our expertise, but was concentrated on the protists (diatoms, algae, protozoa) and a few multicellular organisms like rotifers. This is nowhere near a complete list for even the areas we samples, but is at best a start in defining a quite diverse “fauna” and “flora.”
The tiny “plants” we call diatoms are now known to produce at least 20% of the oxygen we breathe (some say as much as 50%), so they are a fairly big deal. They also sequester large amounts of carbon and thus help lessen the greenhouse effect. Occasionally blooms of some species (e.g. Pseudonitzschia sp.) cause poisoning, but only a few species are involved. We discovered over 20 genera and possibly 50 species in the samples. The number of individuals is staggering and must number into the trillions in a pond, marsh or seacoast. Diatoms are photosynthetic (they use sunlight and carbon dioxide to produce glucose and these excrete oxygen in the process) and their chloroplasts are easily visible under the microscope in living specimens. These organisms are divided into centric and pennate species and a fair number of pennate diatoms have the power of motion. Moving species all have grooves in their shells called a raphe. We still are not sure how these species move. Their shells, called frustules, are composed of inter-fitting halves, much like old-fashioned pill boxes, and are composed of hydrated silicon dioxide with the same chemical composition of opal. Since diatoms have to respire and photosynthesize, the frustules are filled with tiny holes and the resulting sculpturing can be quite beautiful. Because their “shells” are glassy, they fossilize well and deposits of diatomite are common around the world. They apparently originated in the Jurassic, while dinosaurs ruled the earth, but really speciated heavily in the world’s oceans in the Eocene, during the last major runaway greenhouse. Once they were discovered, diatoms became a focus of amateur and professional biologists and numerous microscope slides of preserved material from living forms and fossils were produced, especially in the late 19th and early 20th centuries. These included samples from Arctic and Antarctic expeditions and material from dredgings taken by the first real oceanographic expedition by the H. M. S. Challenger in the 1870s. Here is an example of a diatom from that period.
A few of the diatoms collected during our study are shown below:
There was one organism that is now technically a bacterium that we discovered in our samples. It is a cyanobacterium, formerly known as a blue-green alga – Oscillatoria. Unlike other Eubacteria this organism can be seen without oil-immersion (Necessary with light microscopes at magnifications of 1000X) Oscillatoria also has another distinction- like raphid diatoms it can move! In this case it does not move in a straight line, but oscillates, which gives the genus its name. It is found in freshwater over much of the planet. Like diatoms, cyanobacteria photosynthesize and produce oxygen.
Green algae are common in freshwater and at least some golden algae. The genus Spirogyra represents the commonest of the green algae and includes several hundred species. These are photosynthetic and give the green color to puddles in their role as pond scum. Under the microscope, Spirogyra is very beautiful.
In a preliminary sample at Willow Creek, Richman was able to get a golden alga that we never saw again. This is a species of Hydrurus. The puddle has since dried up and so we sampled the creek itself for all of the rest of our observations.
Many protists were thought to be animals as recently as 50 years ago and were included in invertebrate zoology classes at universities as Protozoa. These included flagellates, amoebae and ciliates. We would very likely gotten more of these if we had added nutrients to our samples, but that is another level. We saw one amoeba, several ciliates and several flagellates. Euglena viridis was one of the flagellates and it is photosynthetic like the diatoms. In the salt water off Edmonds Fishing Pier, there were several species of dinoflagellates as well.
Of the multicellular organisms we found in our samples there were at least three Rotifers, as well as two kinds of crustacea: water fleas and copepods. We also observed a planarian flatworm, another flatworm, and a midge larva.
All in all we were able to determine at least 60 species of microorganisms in eight full samples and three pre-samples. There are almost certainly hundreds, if not thousands.
The main point of our short project was to demonstrate the importance of aquatic microorganisms in the familiar ecosystems around Edmonds. While some microorganisms may be dangerous or detrimental to human interests and health, the vast majority are necessary for the proper functioning of the systems in which they live. We do not usually even think of the teaming numbers of unseen organisms, but do notice the more observable life forms like fish, birds and mammals, that in the ultimate need these creatures. The oxygen we breathe, the carbon dioxide and other gases that influence our climate and the food we eat also depend on these multitudes. Thus anything that disturbs the dynamic balance that is provided by them can affect us in unpredictable and often detrimental ways. We would be wise to keep them in mind, even if they are invisible to us.
A more complete exposition on our snapshot study of Edmonds Parks microorganisms will appear in the British online journal Micscape.
Thanks to the encouragement from Jennifer Leach at Edmonds Parks, Recreation and Cultural Services and the citizen scientists at inaturalist and Diatom Forum, who helped in the identification of several of our microorganisms. However, we alone are responsible for any errors.
— By David B. Richman and Mary Ann Tiffany