October 15, 2021

Fuel.

Some 6 years into our adventure at Tannin Aquatics, the idea of tossing all sorts of botanical materials into our aquariums for the purposes of creating a diverse, functional ecological system is becoming more widely accepted in the hobby.

However, the real breakthrough with botanicals comes when you let them fully decompose in your aquarium.

Yeah, I'm talking about stuff breaking down in your tank. The idea of those nice crispy leaves and pristine seed pods softening, shedding their tissues, and ultimately turning into little bits and pieces of materials.

It requires a little understanding of the process- as well as an appreciation for what is actually occurring in order for most hobbyists to accept this. By making those mental shifts to accept these process and foster them- as well as their rather unique "aesthetics"- we are helping to unlock potential benefits for our aquariums as never before.

And it starts with stuff breaking down. The process of decomposition.

Decomposition is an amazing process by which Nature processes materials for use by the greater ecosystem. It's the first part of the recycling of nutrients that were used by the plant from which the botanical material came from. When a botanical decays, it is broken down and converted into more simple organic forms, which become food for all kinds of organisms at the base of the ecosystem.

In aquatic ecosystems, much of the initial breakdown of botanical materials is conducted by detritivores- specifically, fishes, aquatic insects and invertebrates, which serve to begin the process by feeding upon the tissues of the seed pod or leaf, while other species utilize the "waste products" which are produced during this process for their nutrition.

In these habitats, such as streams and flooded forests, a variety of species work in tandem with each other, with various organisms carrying out different stages of the decomposition process.

And it all is broken down into three distinct phases identified by ecologists.

It goes something like this:

A leaf falls into the water.

After it's submerged, some of the "solutes" (substances which dissolve in liquids- in this instance, sugars, carbohydrates, tannins, etc.) in the leaf tissues rather quickly. Interestingly, this "leaching stage" is known by science to be more of an artifact of lab work (or, in our case, aquarium work!) which utilizes dried leaves, as opposed to fresh ones.

Fresh leaves tend to leach these materials over time during the breakdown/decomposition process. It makes sense, because freshly fallen or disturbed leaves will have almost their full compliment of chlorophyll, sugars, and other compounds present in the tissues. (Hmm, a case for experimenting with "fresh" leaves? Perhaps? We've toyed with the idea before. Maybe we'll re-visit it?)

Cool experiments aside, this is yet another reason why it's not a bad idea to prep your leaves, because it will help quickly leach out many of the remaining sugars and such which could degrade water quality a bit in closed systems.

The second stage of the process is called the "conditioning phase", in which microbial colonization on the leaf takes place. They begin to consume some of the tissues of the leaf- at least, softening it up a bit and making it more palatable for the aforementioned detritivores. This is, IMHO, the most important part of the process. It's the "main event"- the part which we as hobbyists embrace, because it leads to the development of a large population of organisms which, in addition to processing and exporting nutrients, also serve as supplemental food for our fishes!

The last phase, "fragmentation", is exactly what it sounds like- the physical breakdown of the leaf by various organisms, ranging from small crustaceans and shrimp to fungi- and even fishes, collectively known as "shredders." It has been suggested by some ecologists that microbes might be more important than "shredders" in tropical streams.

Fauna composition differs between habitats, yet most studies I've found will tell you that Chironomidae ( insect larvae-think Bloodworms!) are the most abundant in many streams, pools, flooded forests, and "riffles" in the initial period of leaf breakdown!

The botanical material is broken down into various products utilized by a variety of life forms. The particles are then distributed downstream by the current and are available for consumption by a variety of organisms which comprise aquatic food webs.

Six primary breakdown products are considered in the decomposition process: bacterial, fungal and shredder biomass; dissolved organic matter; fine-particulate organic matter; and inorganic mineralization products such as CO₂, NH₄⁺ and PO₄³^-.

An interesting fact: In tropical streams, a high decomposition rate has been related to high fungal activity...these organisms accomplish a LOT!

Interestingly, scientists have noted that the leaves of many tropical plant species tend to have higher concentrations of secondary compounds and more recalcitrant compounds than do leaves of temperate species. Also, some researchers hypothesized that high concentrations of secondary compounds ( like tannins) in many tropical species inhibit leaf breakdown rates in tropical streams...that may be why you see leaf litter beds that last for many years and become known features in streams and river tributaries!

There's a whole lot of stuff going on in the litter beds of the world, huh?

Of course, fungal colonization of wood and botanicals is but one stage of a long process, which occurs in Nature and our aquariums. And, for many hobbyists, once we see those first signs of fungal growths or biofilms, the majority of us tend to reach for the algae scraper or brush and remove as much of it as possible- immediately! And of course, this provides some "aesthetic relief" for some period of time- but it comes right back...because these materials will provide a continuous source of food and colonization sites for fungal growths!

And the idea of "circumventing" this stuff is appealing to many, but the reality is that you're actually interrupting the process. Nature abhors a vacuum, and new growths will return to fill the void, thus prolonging the process.

Why fight it?

Alteration of the botanicals is done chemically via this microbial action; ultimately, the components of the botanicals/leaves (lignin, cellulose, etc.) are broken down near completely. In aquatic environments, photosynthetic production of oxygen ceases in plants, and organic matter and nutrients are released back into the aquatic environment.

All of these organisms work together- in essence, supporting each other via the processes which they engage in.

And, decomposition is a dynamic, fascinating process- part of why we find the idea of a natural, botanical-style system so compelling. Many of the organisms- from microbes to micro crustaceans to fungi- are almost never seen except by the most observant and keen-eyed hobbyist...but they're there- doing what they've done for eons.

They work slowly and methodically over weeks and months, converting the botanical material into forms that are more readily assimilated by themselves and other aquatic organisms.

The real cycle of life!

And another reason why the surrounding tropical forests are so vital to life. The allochthonous leaf material from the riparian zone (ie; from the trees!) as a source of energy for stream invertebrates, insects and fishes can't be understated! When we preserve the rain forests and their surrounding terrestrial habitats, we're also preserving the aquatic life forms which are found there when the waters return.

In the aquarium hobby, we are now accepting the use of botanical materials for a combination of reasons- what we call "functional aesthetics"- the capability of a material to influence the look and the function of the aquarium environment simultaneously.

A real "mental shift..."

Some hobbyists have commented that, as their leaves and botanicals break down the scape as initially presented changes significantly-evolves- over time. Whether they know it or not, they are grasping Takashi Amano's interpretation of "Wabi-Sabi"...sort of. One must appreciate natural beauty at various phases of the aquarium's existence in order to really grasp the concept and appreciate it: To find little vignettes- little moments- of fleeting beauty that need not be permanent to enjoy.

We just plug along, feeding our fishes, doing water exchanges, and growing plants. We tend to our aquascapes, and watch things grow. And, over time, even the most diligently-maintained aquariums tend to look significantly different than when they did when they were first assembled.

And, despite their impermanence, these materials function as diverse harbors of life, ranging from fungal and biofilm mats, to algae, to micro crustaceans and even epiphytic plants. Decomposing leaves, seed pods, and tree branches make up the substrate for a complex web of life which helps the fishes that we're so fascinated by flourish.

And, if you look at them objectively and carefully, these assemblages are beautiful, both in aquariums and in the wild habitats which we strive to replicate. The idea of embracing Nature is not something entirely new or previously unconsidered in the hobby. However, the idea of accepting the look, function, and benefits of natural processes (such as formation of fungal growths and the decomposition of botanical materials) IS.

Of course, when we look at natural ecosystems where leaves and other botanical materials collect, the parallels in look and function between Nature and aquarium become far more obvious!

Understanding the transient nature of botanical materials is absolutely essential for the botanical-style aquarium enthusiast. There are many who prefer a crisp, clean collection of botanicals and leaves in their tanks, and go to great effort to keep them that way...They will remove any leaf that starts to break down or recruit biofilms, and replace them with new ones. If you're up to the task- I say go for it!

For most of us- those of us who've made that mental shift- we let Nature dictate the evolution of our tanks. We understand that the processes of biofilm recruitment, fungal growth, and decomposition work on a timeline, and in a manner that is not entirely under our control.

We realize that botanical materials- with all of their impermanence and imperfection- are "fuel" for ecological processes, which help dictate the diversity and health of our aquariums.

This is another one of those foundational aspects of the natural style of aquarium that we espouse. The understanding that processes like decomposition and physical transformation of the materials that we utilize our tanks are normal, expected, and beautiful things requires us to make mental shifts.

We need to get over the "block" which has espoused a sanitized version of Nature. I hit on this theme again and again and again, because I feel like globally, our community is like 75% "there"- almost entirely "bought in" to the idea of really naturally-appearing and functioning aquarium systems.

Understanding that stuff like the aforementioned decomposition of materials, and the appearance of biofilms- comprise both a natural and functional part of the microcosms we create in our tanks.

Employing natural materials which tend to recruit these life forms during their time in our tanks is actually one of the joys of our hobby pursuits, IMHO.

It's all about how the natural materials that we play with fuel the process of establishing, growing, and maintaining a closed ecosystem in our aquaria. Knowing that the turbid, biofilm-and-fungal-growth-filled aquarium that you've recently set up will evolve over time to a rich, diverse, biologically stable microcosm.

Observing and appreciating this stuff- all of it- rather than instinctively reacting to it with fear or revulsion, is the key to success with botanical-style aquariums. Ask yourself, the next time you're inclined to run for the siphon hose or scraper, why you must remove it? Is it because it's somehow "harmful" to your aquarium?

Or, perhaps- could it be that we are so indoctrinated in hobby practice to remove anything which somehow offends our aesthetic sensibilities of what we think- or have been told for generations- that a "healthy" aquarium should look like?

DIg. Dig deep...and ask yourself those questions.

Consider that removing some of these things- decomposing leaves, detritus, biofilm and frugal growths, not only potentially removes someone's food source from the system- it interrupts fundamental and beneficial ecological processes which, despite their aesthetics, provide extremely valuable services for all of the life forms in your aquarium.

Botanicals are fuel.

Fuel for life. Fuel for natural processes which can yield benefits for our aquariums which we have spent years and countless amounts of money attempting to circumvent in our quest to recreate what Nature offers up for free, for all of those who would but submit to Her processes.

Be strong.

Stay bold. Stay curious. Stay grateful. Stay open-minded. Stay calm...

And Stay Wet.

Scott Fellman

Tannin Aquatics