Homeostasis

The mussel is gone, but the tadpole tank is complete. On a trip to the Habitat for Humanity ReStore, I found a solid end table to place the tank on, as well as an old window screen that Isaac fashioned into a lid for the aquarium. The screen prevents mosquitoes and other bugs from hatching directly into our living room and features a wooden ledge where Isaac and I mounted a grow light, to stimulate plant growth. It is, finally, a real aquarium.

Roughly 12 million US households have an aquarium, which means that the internet is overflowing with advice on aquarium best practices. Use packaged aquarium pebbles, the fish forums command. Test your pH and nitrogen levels, add a filter, and, most egregiously, change out the water in the tank. This is all fine advice if you keep a fish tank. With the exception of some tidepool-adapted sculpin, there aren’t any fish that are adapted to survive in 20 gallons of water, let alone 10 or 5 gallons. By plunking some goldfish or gobies into a tiny environment, it’s necessary to regulate their conditions strictly.

Tadpoles, however, are perfectly suited to small bodies of water. In fact, they do better in shallow water that heats up quickly, and they survive at much higher rates in bodies of water that are too small to support predatory fish. So, thanks to a combination of misplaced self-confidence and absolute faith in amphibian supremacy, I’ve been forgoing the typical aquarium monitoring procedures, or in other words, I’ve been “winging it”.

The first change I noticed in the tank, after installing a couple inches of rock, sand, and muck on the bottom, and wedging some lakeweeds in there, was a proliferation of algae. Long bright green spaghetti strands coiled in the tank, tangling with the plants and reaching toward the surface. The logical response to the algal bloom would have been to panic, but I took a deep breath. Toad tadpoles are vegetarian. In fact, algae are their favorite food. Sure enough, after a week, almost all the algae had been munched down to little green nubs.

Collecting lake weeds.

In fact, after a couple more weeks, I realized that there wasn’t enough algae in the tank. Such a realization came not from some expensive pet store tester, but from what I have dubbed the “Big Chungus Effect.” Big Chungus, named for an unfunny 2016 internet meme, quickly established himself as the largest tadpole of the lot. Unlike his smaller siblings, Chungus was eating plant leaves, somehow crunching down on their more durable fibers and making me go down to the lake to find replacements after he ate several plants to death.

The smaller tadpoles, lacking the ferocious jaws of Chungus, weren’t growing fast enough, so I began to add slices of cucumber to the tank, and eventually clumps of algae from the lake. The addition of the cucumber, combined with the dead plant matter, raised the nitrogen levels in the tank. Nitrogen is the main ingredient in most commercial fertilizer, because plants require it to make chlorophyll, that green-colored photosynthesis motor.

Tadpoles love cucumber!

Let’s zoom out for a second. Nitrogen is the most plentiful element in our atmosphere, making up a whopping 70% of the molecules zipping above our heads and through our lungs. So it might seem a little strange that plants are normally short on Nitrogen supplies. That’s because most of the nitrogen atoms in the world are locked together as N2 (think Nitrogen x2) molecules. N2 is really difficult to break apart; it’s so glued that humans didn’t figure out how to pry it apart until the early 1900s, when German chemists Haber and Bosch tried applying very unsafe levels of heat and pressure to N2, Hydrogen, and a metal catalyst. Their success blew open the door on commercial fertilizer production.

At present day, 1% of humanity’s energy is spent breaking apart Nitrogen molecules so they can be used in fertilizer. So much fertilizer is applied, especially in the US, that there is a 4,000 square mile “dead zone” where the Mississippi empties into the Gulf of Mexico. The dead zone is caused by an overabundance of life – algae multiply like crazy when Nitrogen levels are high, and then the algae dies, fueling in turn a boom of bacteria. The bacteria use all the oxygen, the fish die, the cycle repeats. These dangers were at the forefront of my mind when I noticed new algae growth on the glass walls of my tadpole aquarium.

Someone more responsible than me would have taken a toothbrush and cleaned off the algae, but I decided to trust my living system. Not only will the tadpoles eat the additional algae, but so will snails. And boy, do I have snails. I started with two or three. These will be great for keeping the glass clean, thought I. I watched with delight as the largest snail glued himself to the surface tension on the water and spun in circles. Then the snails started to get busy, laying clear jellies of eggs on the leaves of the plants, which hatched into pin-head sized babies.

I’m not sure what technically comprises a snail infestation – but my aquarium certainly qualifies. Ounce for ounce, they could overpower the tadpoles, but thankfully both critters are vegetarians. When the snails are really teensy, their shells are clear, and you can see their miniature pink snail organs. They’re almost undistinguishable from a whole host of tiny freshwater plankton (more on those in a different post).

The snails should have the algae growth under control. Excess Nitrogen will hopefully be absorbed by the quickly growing lake plants (including a small lily pad) and the roots of a propagated pothos house plant. The pothos, a tropical vine, sits on the lid of the aquarium, its roots resting in the water and filtering nutrients found in the copious quantities of snail and tadpole poop.

Pickled carrots? Or an entire water lily plant about to be relocated to my aquarium?

There are so many different species living in the tank (tiny shrimp, diving beetles, algae, duckweed, tadpoles, insect larvae, I could go on) that it has effectively reached homeostasis. Homeostasis comes from two Greek words: hómoios, which means “same”, and stasis, which means standing still. This is the point in any ecosystem, from a 20 gallon tank to a two thousand acre prairie, when the populations of different species – and the nutrients they depend on – remain stable.

It’s an odd way to think about any ecosystem, because nothing in nature stands still. Homeostasis itself is an illusion, an appearance of sameness that only exists at a certain scale. Look too closely, and you will see the rapidly fluctuating populations of bacteria and single-celled organisms. Zoom out too far, and you’ll reach the walls of your aquarium, the edge of your forest, the outer limits of your planet’s atmosphere. Scale defines ecology, and ecologists have spent the last few hundred years separating living things into species, families, ecosystems and biomes. But scale also ecology is defied by scale, because other creatures do not care about the rules we set. The trick to being an ecologist is putting the rules on the shelf – at shoulder height so they’re easy to reach just in case – and opening your senses to the flow of poop, the blooming of algae, and the constant of change.