March 09, 2023

Beyond the superficial aspects of "natural" aquariums

Okay, I'm sort of getting back into the game from a long-overdue self-imposed aquarium "sabbatical", and I'm looking at things a bit more objectively than before. Well, I was always pretty objective, but it became increasingly challenging for me to keep it that way after seeing how the hobby seems to be coalescing around aesthetics above almost all else when talking about "natural" aquarium systems.

It's really obvious wen you step away and sort of explore social media from afar. Like, we have these ideas out there, yet the hobby in it's most popular form is embracing a really superficial approach to representing "Nature" in our tanks.

During my "time away", I've had lots of discussions with all sorts of fellow hobbyists about how we approach the creation of our aquariums. It was enlightening to interact with people from different hobby specialities, to not only understand their POV, but to see some common threads in our philosophies and approaches.

One of the topics which kept coming up during and after conversations was thinking on a deeper level about how to more faithfully replicate the natural habitats of many of the fishes that we love so much. And Im talking about this from the function al aspect- not simply creating cool-looking tanks. Having a bit of faith that the way Nature functions is as engaging and beautiful as the way it looks.

And of course, the the idea that there are all sorts of interesting influences on these natural habitats created by the surrounding terrestrial environment and the microbial associations which occur in the substrates, leaves, wood, and other materials which comprise them.

The relationship between terrestrial habitats and the aquatic environment is becoming increasingly apparent- particularly in areas in which "blackwater" habitats are found. And, the lack of suspended sediments, which create a "nutrient poor" condition in these aquatic habitats, doesn't do much to facilitate "in situ" production of aquatic food sources; rather, it places the emphasis on external factors.

Think about that for a second.

Many blackwater systems are simply too poor in nutrients to offer alternative food sources to fishes.The importance of the relationship between the fishes and their surrounding terrestrial habitat (i.e.; the forests which are inundated seasonally) is therefore obvious. That likely explains the significant amount of insects and other terrestrial food sources that ichthyologists find during gut content analysis of many fishes found in these habitats.

And, as we've hinted on previously- the availability of food at different times of the year in these waters also contribute to the composition of the fish community, which varies from season to season based on the relative abundance of these resources.

Another example of these unique interdependencies between land and water are when trees fall.

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.

Of all of the botanical materials that we employ in our aquariums, none are more common, well-studied, or simply ubiquitous in aquatic habitats than leaves.

In nature, leaf litter zones comprise one of the richest and most diverse biotopes in the tropical aquatic ecosystem, yet they are seldom replicated in the aquarium. Now, more so than in years past, but I would not call aquariums configured to replicate these habitats "common."

Why?

I think this has been due, in large part- to the lack of a real understanding about what this biotope is all about- not to mention, the understanding of the practicality of creating one in the aquarium.

It's important to understand that a leaf litter bed in Nature- or the aquarium, for that matter- is a rich ecosystem, providing food and shelter to a diverse community of organisms, ranging from fungi to bacterial biofilms.

And of course, fishes and invertebrates which live amongst and feed directly upon the fungi and decomposing leaves and botanical materials contribute to the breakdown of these materials as well! Aquatic fungi can break down the leaf matrix and make the energy available to feeding animals in these habitats.

And look at this little gem I found in my research:

"There is evidence that detritivores selectively feed on conditioned leaves, i.e. those previously colonized by fungi (Suberkropp, 1992; Graca, 1993). Fungi can alter the food quality and palatability of leaf detritus, aecting shredder growth rates. Animals that feed on a diet rich in fungi have higher growth rates and fecundity than those fed on poorly colonized leaves. Some shredders prefer to feed on leaves that are colonized by fungi, whereas others consume fungal mycelium selectively..."

"Conditioned" leaves, in this context, are those which have been previously colonized by fungi! They make the energy within the leaves and botanicals more available to higher organisms like fishes and invertebrates!

It's easy to get scared by this stuff...and surprisingly, it's even easier to exploit it as a food source for your animals! This is a HUGE point that we can't emphasize enough.

Here is an interesting except from an academic paper on Amazonian Blackwater leaf-litter communities by biologist Peter Alan Henderson, that provides some context for those of us considering replicating these communities in our aquaria:

"..life within the litter is not a crowded, chaotic scramble for space and food. Each species occupies a sub-region defined by physical variables such as flow and oxygen content, water depth, litter depth and particle size…

...this subtle subdivision of space is the key to understanding the maintenance of diversity. While subdivision of time is also evident with, for example, gymnotids hunting by night and cichlids hunting by day, this is only possible when each species has its space within which to hide.”

In other words, leaf litter beds facilitate and accommodate diverse populations of fishes, and we should consider this when creating and stocking our botanical-style aquairum systems.

Some litter beds form in what stream ecologists call "meanders", which are stream structures that form when moving water in a stream erodes the outer banks and widens its "valley", and the inner part of the river has less energy and deposits silt- or in our instance, leaves.

There is a whole, fascinating science to river and stream structure, and with so many implications for understanding how these structures and mechanisms affect fish population, occurrence, behavior, and ecology, it's well worth studying for aquarium interpretation! Did you get that part where I mentioned that the lower-energy parts of the water courses tend to accumulate leaves and sediments and stuff?

It's logical, right? And it's also interesting, because, as we know, fishes and their food items tend to aggregate in these areas, and embracing the "theme" of a litter/botanical bed or even wood placement, in the context of a stream structure in the aquarium is kind of cool!

Incorporating leaf litter in our aquariums opens up all sorts of possibilities for interesting experiments ranging from community displays to fry rearing systems. You can go with just a few leaves in your tank- or really go crazy with a deep bed of leaf litter in your tank. It's wide open for experimentation.

How do you create one?

Well, it's not particularly complicated, really. Simply add a selection of the prepared leaves of your choice to your aquarium! I mean, simple... In a brand new tank, devoid of fishes, you can add as many as you want all at once. In an established, populated tank, you should build up the depth and quantity gradually over the course of several weeks, monitoring any environmental impacts regularly, to gauge for yourself any issues which may arise along the way. Common sense, right?

How many leaves, what kind, and how often to add them is a topic open for discussion and debate, really.

I periodically ponder and discuss the idea of creating a really deep litter bed in an aquarium, to more accurately replicate some of the litter beds found in South America, Asia, Africa, and elsewhere. By "deep", I'm talking 6"- 12" (15.24cm-30.48cm). Yes, there are deeper litter beds in these areas (several feet in depth); however, for practical aquarium display purposes, I think the rational "upper limit" is likely more like the 12" (30.48cm) range.

Or, is it?

Maybe you can go as deep as you want. We simply don't really know right now. No one is really experimenting with this at the moment. As a hobby, we're too caught up in the "look", right?

Okay, back to the function thing:

In these habitats, fishes, and the other organisms present- and their processes- create not only the basis of a "food web", but the development of an entire community of co-dependant organisms, which work together to process nutrients and support life forms all along the chain.

When we encourage, rather than remove these organisms when they appear, we're helping perpetuate these processes. I can't stress how important it is to let these various organisms multiply.

And we need to re-think our relationship with leaf litter, detritus, decomposing botanical materials, and sediments in our tanks.

Yes, I'm asking you to not only "leave them be" -but to encourage their accumulation, to foster the development and prosperity of the organisms which "work" them.

Once again, I have to at least ask the rather long question, "Are these things (detritus; decomposing leaves) really problematic for a well-managed aquarium, optimized to take advantage of their presence Or, do they constitute an essential component of a closed aquatic ecosystem...One which can actually provide some benefits (ie; supplemental nutrition) for the resident fishes and the community of life forms which support them?"

Oh, what a question, huh?

The beauty is that we are all able to help answer it.

Blurring the lines between nature and the aquarium, at the very least, from an aesthetic sense- and most important, from a "functional" sense, proves just how far today's hobbyists have come...how damn good you are at what you do. And how much more you can do when you turn to nature as an inspiration, and embrace it for what it is.

I'm not telling you to totally turn your back on the modern popular aquascaping scene; to disregard or dismiss the brilliant work being done by aquascapers around the world, to develop a sense of superiority or snobbery, and conclude that everyone who loves this stuff is a sheep...

Noooooo.

Not at all.

I'm simply the guy who's passing along the gentle reminder from Nature that we have this great source of inspiration that really works! Rejoice in the fact that Nature offers an endless variety of beauty, abundance, and challenge- and that it's all there, free for us to interpret it as we like.

It's not all perfect "rule of thirds", "designer rocks", or flawless layouts and such.

Some of us just happen to like things bit more "natural" than others...

Blur the lines.

And, part and parcel in this philosophy is the practice of evolving your aquarium in ways that you may not have initially envisioned. Cutting yourself some slack...

Huh?

Okay, let's say that you're kind of over your Southeast Asian Cryptocoryne biotope, and ready to head out to South America. So, rather than tearing up the entire tank, removing all of the plants, the hardscape, the leaves and botanicals, and the substrate, you opt to remove say, only the plants and perhaps the driftwood/rocks from the tank; exchange a good quantity of the water.

You leave the botanicals and substrate intact and move on from there...

Woooah! Crazy! You're a fucking rebel...

I know. I know. This isn't exactly earth-shattering.

Yet, in our world of the botanical-method aquarium, the idea of leaving the substrate and leaf litter/botanical "bed" intact as you "remodel" isn't exactly a crazy one. And conceptually, it's sort of replicates what occurs in Nature, doesn't it? A bit different from the "popular" "Instagram Aquascaping" approach of, "I'm done with this tank...Let's just tear it apart and start with an empty glass box!"

Most underwater habitats emerge, accumulate, populate, evolve...and change.

Constantly.

Yeah, think about this for just a second...

As we almost constantly discuss, habitats like flooded forests, meadows, vernal pools, igarape, and swollen streams tend to encompass terrestrial habitats, or go through phases where they are terrestrial habitats for a good part of the year. Or, perhaps they're different types of aquatic habitats at different times of the year.

In these wild habitats, the leaves, branches, soils, and other botanical materials remain "in place", or are added to by dynamic, seasonal processes like current, weather, and cyclical leaf drop from trees. For the most part, the soil, branches, and a fair amount of the more "durable" seed pods and such remain present during both phases.

The formerly terrestrial physical environment is now transformed into an earthy, twisted, incredibly rich aquatic habitat, which fishes have evolved over eons to live in and utilize for food, protection, and complex, protected spawning areas.

I cannot stress how insanely cool and important it is to recognize this dynamic and its impact on fishes. We've talked about this endlessly here- but each time I think about and play with the idea, my mind goes crazy with inspiration!

It's a really big world out there. There's a lot to inspire, and lots to replicate out there.

Stay inspired. Stay passionate. Stay curious. Stay committed...

And Stay Wet.

Scott Fellman

Tannin Aquatics