March 07, 2020

The breakdown on...the breakdown!

Of all the processes which we foster and observe in our botanical-style aquariums, none is more fundamental than the decomposition of the leaves, seed pods, and bark that we play with in our practice. And the most amazing thing is that the very processes that we see in our aquariums have been occurring in Nature for eons.

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 fishes 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. Hmm, a case for experimenting with "fresh" leaves? Perhaps? On the other hand, 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.

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^-. In tropical streams, a high decomposition rate has been related to high fungal activity...they 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!

A lot of stuff going on in the litter beds of the world, huh?

This 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 our aquariums, we're just beginning to appreciate the real benefits of using leaves and botanicals. Not just for cool aesthetics or to "tint" the water- but to create truly natural, ecologically stable aquatic systems for the health and well-being of the fishes we love so much!

And it all starts with leaves falling into the water and...breaking down.

It's still early days.

There is so much to learn and experiment with. Every single one of us, when we embark on a botanical-style aquarium adventure- is playing a key role in contributing to the "state of the art" of the aquarium hobby! Every contribution is important...

Enjoy the process!

Stay curious. Stay observant. Stay experimental. Stay bold...

And Stay Wet.

Scott Fellman

Tannin Aquatics