December 09, 2021

The joys of allochthonous input.

If you had to ask me about the "prototype" for the botanical method aquarium, it would have to be the flooded blackwater forests of Amazonia, the igapo. Perhaps nowhere else is the relationship between terrestrial and aquatic environments so vividly demonstrated than in these unique ecosystems.

The concept of allochthonous inputs, which are materials arriving into a habitat (in our case, the aquatic one) from outside of it (the terrestrial one), like fruits, seeds, insects, and plant parts, are important food sources to many fishes. Many midwater characins consume fruits and seeds of terrestrial plants, as well as terrestrial insects.

It’s not uncommon for a tree to fall in the rain forest, with punishing rain and saturated ground conspiring to easily knock over anything that's not firmly rooted. When these trees fall over, they often fall into small streams, or in the case of the varzea or igapo environments in The Amazon that I'm totally obsessed with, they fall and are submerged in the inundated forest floor when the waters return.

And of course, they immediately impact their (now) aquatic environment, fulfilling several functions: Providing a physical barrier or separation from currents, offering territories for fishes to spawn in, providing a substrate for algae and biofilms to multiply on, and providing places for fishes forage among, and hide in. An entire community of aquatic life forms uses the fallen tree for many purposes. And the tree trunks and parts will last for many years, fulfilling this important role in the aquatic ecosystems they now reside in each time the waters return.

Shortly after falling into the water, fungi and other microorganisms act to colonize the surfaces, and biofilms populate the bark and exposed surfaces of the tree. Over time, the tree will impart many chemical substances, (humic acids, tannins, sugars, etc.) into the water.

The fallen tree literally brings new life to the waters.

Let's summarize: The materials which comprise the tree are known in ecology as "allochthonous material"- something imported into an ecosystem from outside of it. (extra points if you can pronounce the word on the first try...) And of course, in the case of fallen trees, this includes includes leaves, fruits and seed pods that fall or are washed into the water along with the branches and trunks that topple into the stream.

And the life forms of the terrestrial environment become important to the aquatic habitat as well. Insects, specifically, are really important to fishes in blackwater ecosystems. In fact, it's been concluded that the the first link in the food web during the flooding of forests is terrestrial arthropods, which provide a highly important primary food for many fishes.

As we've already established, the relationship between the terrestrial and aquatic habitats is important beyond just the food input/production benefits. The reality is that the relationship is absolutely foundational- part of the very existence of the habitats themselves!

The leaves, branches, seed pods, etc. which end up submerged in these habitats following the seasonal inundation essentially create the biology and the structural/physical part of the benthic environment of the igapo.These systems are intimately tied to the surrounding terrestrial environment.

Even the permanent rivers have a strong, very predictable "seasonality", which provides fruits, seeds, and other terrestrial-originated food resources for the fishes which reside in them. It's long been known by ecologists that rivers with predictable annual floods have a higher richness of fish species tied to this elevated rate of food produced by the surrounding forests.

AQUARIUM PRACTICE AND THE CONCEPT OF ALLOCHTHONOUS INPUTS

Incorporating botanical materials in our aquariums for the purpose of creating the foundation for biological activity is the starting point. Leaves, seed pods, twigs and the like are not only "attachment points" for bacterial biofilms and fungal growths to colonize, they are physical location for the sequestration of the resulting detritus, which serves as a food source for many organisms, including our fishes.

Think about it this way: Every botanical, every leaf, every piece of wood, every substrate material that we utilize in our aquariums is not only a physical component- it's a potential component of food production!

The initial setup of your botanical-style aquarium will rather easily accomplish the task of facilitating the growth of said biofilms and fungal growths. There isn't all that much we have to do as aquarists to facilitate this but to simply add these materials to our tanks, and allow the appearance of these organisms to happen.

You could add pure cultures of organisms such as Paramecium, Daphnia, species of copepods (like Cyclops), etc. to help "jump start" the process, and to add that "next trophic level" to your burgeoning food web.

In a perfect world, you'd allow the tank to "run in" for a few weeks, or even months if you could handle it, before adding your fishes- to really let these organisms establish themselves. And regardless of how you allow the "biome" of your tank to establish itself, don't go crazy "editing" the process by fanatically removing every trace of detritus or fragmented botanicals.

When you do that, you're removing vital "links" in the food chain, which also provide the basis for the microbiome of our aquariums, along with important nutrient processing. So, to facilitate these aquarium food webs, we need to avoid going crazy with the siphon hose! Simple as that, really!

Yeah, the idea of embracing the production of natural food sources in our aquariums is elegant, remarkable, and really not all that surprising. They will virtually spontaneously arise in botanical-style aquariums almost as a matter of course, with us not having to do too much to facilitate it.

It's something that we as a hobby haven't really put a lot of energy in to over the years. I mean, we have spectacular prepared foods, and our understanding of our fishes' nutritional needs is better than ever.

Yet, there is something tantalizing to me about the idea of our fishes being able to supplement what we feed. In particular, fry of fishes being able to sustain themselves or supplement their diets with what is produced inside the habitat we've created in our tanks!

A true gift from Nature.

I think that we as botanical-method aquarium enthusiasts really have to get it into our heads that we are creating more than just an aesthetic display. We need to focus on the fact that we are creating functional microcosms for our fishes, complete with physical, environmental, and nutritional aspects.

And when you think about it- getting back to the whole botanical method of aquarium keeping- the idea that various materials can influence the physical characteristics and even the ecology of the aquarium is the game.

And you'll note that we've sort of embraced the moniker "botanical method" of late as a transition from "botanical style" to better describe what we do. The use of the word "style" seemed to incorrectly imply that what we do is an "aquascaping style", rather than a methodology of creating a functional ecology within the aquarium, and we really wanted to draw that distinction!

In our instance, yeah- the aesthetics are unique and different, but a significant part of them is derived from the function of botanical materials interacting with the aquatic environment.

With more and more attention being paid the overall environments from which our fishes come-not just the water, but the surrounding areas of the habitat, we as hobbyists will be able to call even more attention to the need to learn about and protect them when we create aquariums based on more specific habitats.

We should look at nature for all of the little details it offers. We should question why things look the way they do, and postulate on what processes led to a habitat looking and functioning the way it does- and why/how fishes came to inhabit it and thrive within it.

It's a fun and fascinating journey, that will not only yield greater understanding of our fishes, but of the precious and fascinating environments from which they come. And a greater appreciation for the functions and vulnerabilities of these wild ecosystems means that we'll be in a better position than ever as aquarists to call attention to the perils that they face.

And when we inspire non-aquarists to understand and learn more about this stuff- the planet wins.

Not a bad return on the investment of studying the unique concept of allochthonous input, right?

Stay resourceful. Stay curious. Stay thoughtful. Stay observant. Stay creative...

And Stay Wet.

Scott Fellman

Tannin Aquatics