Healthy pond water is teeming with tiny organisms, but most can only been seen under a microscope.
Microorganisms are single celled organisms that are found within four kingdoms – the plant kingdom, bacteria, fungi, and protozoa. While it may seem at first as though all microorganisms are the same, they are actually perhaps the most diverse group of organisms in the world, their minute size being one of the few things that they share in common with one another.
These microorganisms are at the very base of food webs and ecological functions; without them, life simply would not be possible. From generating oxygen to facilitating decomposition to promoting the carbon cycle to releasing nutrients that otherwise would be bound up in nature and not available to the rest of us living things, the world as we know it today simply would not exist were it not for microorganisms and bacteria.
In ponds, the types of bacteria and microorganisms found differs depending on the type of water body – perhaps predictably, natural ponds contain a greater diversity of these beneficial organisms than do most manmade ponds.
Types of Pond Bacteria & Microorganisms
There are many thousands of types of bacteria and microorganisms found in aquatic ecosystems, including your personal pond. The main aquatic groups include arthropods, bacteria, protozoa, hydras, fungi, phytoplankton, and algae:
A Water Mite. Photo by Anatoly Mikhaltsov, available under a Creative Commons Attribution-Share Alike 4.0 International license.
Arthropods include micro and macroinvertebrates such as tardigrades (water bears), crustaceans, some insect larvae, and water mites among others, and most are visible without the use of a microscope. These unique and varied organisms serve a variety of functions – food for other creatures, such as fish; soil aeration; consumption of other microorganisms, like algae, and potentially problematic creatures like mosquito larvae (though mosquito larvae are themselves considered arthropods); and decomposition of organic matter. The size of these creatures really varies, from the size of the period at the end of this sentence to a large monarch butterfly (yep, those are arthropods, too!). In manmade ponds, the presence of some of these is good, while others may indicate poor water quality. For example, tardigrades are found in virtually any spot with dampness, whether that be in moss, a puddle, or your pond. They’re important for proper ecosystem functioning, and your pond should certainly have them. Others, like mosquito larvae, could mean that your pond is too stagnant and your water quality needs to be closely monitored and adjusted.
Cyanobacteria. Photo by Matthew J Parker, available under a Creative Commons Attribution-Share Alike 3.0 Unported license.
As you likely know, there are good bacteria and bad bacteria. While this group often gets a bad rep, ecosystems and the organisms within them (including us!) would die without them. They are among the tiniest and oldest microorganisms on Earth, and can be found virtually everywhere – from a tiny drop of rain to the cap of an ink pen. They are able to multiply exceedingly quickly, making them exceptional at aiding in decomposition in ecosystems and thus cycling nutrients. Specifically, there are heterotrophic bacteria and autotrophic bacteria. The former are the ones responsible for decomposition and nutrient cycling (and can also help to control algae populations by reducing the nutrients that are available to them), while the latter are typically known as cyanobacteria (often misleadingly called blue-green algae even though they are not actually algae).
Cyanobacteria are tricky – you want some in your pond, but not too much. Cyanobacteria have evolved a symbiotic relationship with some species of algae and fungi (and in fact, plant chloroplasts evolved from cyanobacteria long ago, so we have them to thank for a great deal!), and are responsible for fixing nitrogen so that it is available for other organisms to use. However, too much cyanobacteria indicates poor water quality and is most often the culprit behind green, foul-smelling water, so you’ll have to be sure to monitor your water quality daily.
Blepharisma japonicum. Photo by Frank Fox, available under a Creative Commons Attribution-Share Alike 3.0 Germany license.
Protozoa are microscopic, unicellular organisms that resemble animals in that they must consume other organisms in order to obtain the nutrients that they need to live. For example, bacteria help break down organic matter, and protozoans in turn feed on both the bacteria and the detritus (and in turn are eaten by zooplankton, which in turn are consumed by invertebrates, which are in turn devoured by fish, and so on). Without protozoans (which consume as much as 50% of bacteria), bacteria would be able to build up to potentially harmful levels, and also without protozoans, an exceedingly critical link in the food web would be removed, severely crippling the ecosystem as a whole and limiting the plants and animals that would be able to survive in it.
Protists (or protozoans) are quite fascinating little creatures – they are neither plant nor animals, but rather belong to a group entirely their own with an estimated 50,000 plus species. Common species found in ponds include Euglena, Paramecium, amoebas, and ciliates. Most protozoans are considered beneficial, performing the duties mentioned above and also known to create something called biofilm, which is essentially a slimy layer that can contain protozoa, bacteria, and/or fungi and is fed on by a variety of organisms. Others (about one third of protozoa species), however, are parasitic and can cause diseases such as giardia. Overall, though, having protozoa in your pond is a very good and necessary thing – without them, your pond ecosystem would have a very difficult time functioning.
Hydras. Photo by Stephen Friedt, available under a Creative Commons Attribution-Share Alike 3.0 Unported license.
Hydras are predatory freshwater microorganisms, technically considered animals, that occur primarily in ponds, lakes, and other slow-moving water bodies. They feed on a variety of creatures, though chiefly insect larvae and small crustaceans, and interestingly enough are not known to die of old age but rather only via injury, disease, starvation, or being eaten. They have extremely tiny tentacles and attach themselves to rocks, logs, and aquatic vegetation, where they feed on whatever floats by them or is also on that surface. They are present in most ponds, and not really considered either good or bad. Some hydra species have developed a mutualistic relationship with algae – the hydra feed on things that would otherwise predate on the algae, while the algae produce photosynthetic compounds that can be utilized as a food source by the hydra.
Fungi can grow large, but are in-fact single celled organisms.
Because fungi are typically so easy to see and relatively large, it can be odd to think of them as microorganisms. However, fungi are indeed single celled organisms that start off quite small, and may also exist in small filaments called hyphae (which often have a mutualistic relationship with plant roots – they help the plant obtain nutrients from the soil, and the roots in turn give off compounds that can be used by the fungi).
Fungi are heterotrophic and release enzymes into the surrounding environment that break down compounds and nutrients into forms that are usable by the fungi and other organisms. Through this, they aid in nutrient cycling, decomposition, and provide a valuable food source to other organisms. In fact, fungi are one of the only organisms that are able to break down tough plant structural compounds such as lignin, tannins, and cellulose, and as such play a crucial role in aquatic plant matter decomposition. Through this, they help prevent the buildup of nutrients in your pond, thus promoting healthy water quality.
Image of phytoplankton under a microscope.
Phytoplankton are floating, microscopic plants that prefer still water, like that of ponds or the deep ocean. In streams and rivers, little to no phytoplankton exist because the faster flowing waters wash them away more quickly than they are able to reproduce. They are single celled organisms that often gather together in colonies for survival, and provide a critical food source for zooplankton, aquatic invertebrates, and some fish species. However, algae love phytoplankton, and so if phytoplankton numbers are high, algae numbers are also likely to be high and have the potential to lead to algal blooms. You can help control their numbers by incorporating a bit more flow into your pond, via an aerator, pump, or waterfall, though you won’t want to disturb the water so much as to remove them completely.
Diatom Algae. Photo by Berezovska, available under a Creative Commons Attribution-Share Alike 4.0 International license.
Perhaps the most well-known organism among pond owners, algae can either be microscopic or gather together to form large colonies. Algae are exceptionally important in pond ecosystems, as they are at the base of the food web – they are consumed by insects, which are in turn consumed by fish, birds, herps, and various mammals. Some animals will also directly eat algae. In addition, alga generate oxygen and aid in nutrient cycling – it’s only when their numbers get out of control that algae become a problem, as is discussed in our article on the different types of algae found in ponds.
The number of algae species is widely contested, ranging from estimates of 1 million to 350 million. Of course, some algae are helpful while others tend to be more harmful. Diatoms, for example, are never bad no matter how many there are. In fact, they’re responsible for producing anywhere from 25 to 40% of the world’s oxygen (more than all of the rainforests combined), and really don’t look like typical algae at all. They look more like tiny glasslike structures with intricate patterns in them.
Other species, like euglena, are more problematic because you won’t even know that they’re there until a bloom occurs, turning your pond bright red and severely damaging the water quality until you’re able to get the population under control – which is no small task considering euglena doesn’t respond to any known biological or manual control methods. As always, monitor your water quality regularly and you’ll greatly minimize the risk of algae (or any of the microorganisms covered here) becoming problematic.