April 14, 2020

A multifaceted microcosm...

One of the concepts I like most of all when it comes to botanical-style aquariums is how well they lend themselves to fostering a complete community of organisms. Yeah, because of the very "operating system" of our tanks, which features decomposing leaves, botanicals, soils, roots, etc., we are able to create a remarkably rich and complex population of creatures within them.

This is one of the most interesting aspects of a botanical-style aquarium: We have the opportunity to create an aquatic microcosm which provides not only unique aesthetics- it provides nutrient processing, and to some degree, a self-generating population of creatures with nutritional value for our fishes, on a more-or-less continuous basis.

True "functional aesthetics", indeed!

An important part of this little microcosm are fungi.

Yeah, you heard me. Fungi.

Fungi reproduce by releasing tiny spores that then germinate on new and hospitable surfaces (ie, pretty much anywhere they damn well please!). These aquatic fungi are involved in the decay of wood and leafy material. And of course, when you submerge terrestrial materials in water, growths of fungi tend to arise.

Anyone who's ever "cured" a piece of aquatic wood of almost any type for your aquarium can attest to this!

Fungi tend to colonize wood because it offers them a lot of surface area to thrive and live out their life cycle. And cellulose, hemicellulose, and lignin- the major components of wood and botanical materials- are degraded by fungi which posses enzymes that can digest these materials! Fungi are regarded by biologists to be the dominant organisms associated with decaying leaves in streams, so this gives you some idea as to why we see them in our aquariums, right?

And of course, fishes and invertebrates which live amongst and feed directly upon the fungi and decomposing leaves and botanicals 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.

And of course, the same goes for our buddies, the biofilm.

And biofilms are interesting, in and of themselves. Understanding the reasons they arise and how they propagate can really help us to appreciate them!

We've discussed this before; however, let's revisit the process one more time:

It starts with a few bacteria, taking advantage of the abundant and comfy surface area that leaves, seed pods, and even driftwood offer. The "early adapters" put out the "welcome mat" for other bacteria by providing more diverse adhesion sites, such as a matrix of sugars that holds the biofilm together. Since some bacteria species are incapable of attaching to a surface on their own, they often anchor themselves to the matrix or directly to their friends who arrived at the party first.

These bacteria and fungi are all participants in a rather grand process of nutrient utilization- both in Nature, and in our aquariums. And it all starts with adding botanicals and leaves to our systems. This is absolutely analogous to what happens in Nature.

When leaves enter tropical streams and other bodies of water, fungal colonization causes leaves to increase nitrogen content (because of fungal biomass) and leaf maceration. This is known by aquatic ecologists to be evidence of microbial colonization. There are many different stages in the process, starting with the leaching of materials from the cells of the botanicals during initial submersion, in which soluble carbon compounds are liberated in the process. A rapid release of phosphorus accompanies this leaching.

Of course, the process ultimately leads to physical breakdown and/or fragmentation of the leaves and botanicals into smaller "pieces", which possess larger amounts of surface area for microbial attachment. Extensive ecological studies done by scientists specifically in regard to leaf litter have yielded a lot of information about this process.

The fungi known as aquatic hyphomycetes produce enzymes which cause leaf maceration, and in as little as 2 to 3 weeks, as much as 15% of the decomposing leaf biomass in many aquatic habitats is processed by fungi, according to one study I found.

In experiments carried out by aquatic ecologists in tropical forests in Venezuela, decomposition rates were really fast, with 50% of leaf mass loss in streams occurring in less than 10 days!

The ultimate result is the transformation of what ecologists call "coarse particulate organic matter" (C.P.O.M.) into "fine particulate organic matter" (F.P.O.M.), which may constitute an important food source for other organisms we call “deposit feeders” (aquatic animals that feed on small pieces of organic matter that have drifted down through the water and settled on the substrate) and “filter feeders” (animals that feed by straining suspended organic matter and small food particles from water), as well as worms, planaria, and insects.

And of course, these organisms and their processes create not only the basis of a food web, but the development of an entire community of co-dependant organics 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 think about our relationship with 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.

Now, again, I have to at least ask the rather long question, "Are these things (detritus; decomposing materials) really problematic for a well-managed aquarium? 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?"

Many of us have already made a mental shift which accepts the transient, subtle beauty of decomposing botanical materials, tinted water, biofilms, and the like, so it goes without saying that taking it a little further and allowing these materials to completely breakdown to serve as the substrate for our aquatic ecodivesity is simply the next iteration in the management of blackwater/brackish botanical-style aquariums.

So, yeah- there IS a lot to consider when utilizing botanical materials in your aquarium. It's far, far beyond the idea of just "dumping and praying" that has been an unfortunate "model" for how to utilize them in our aquariums for many years. It's more than just aesthetics alone...the "functional aesthetic" mindset- accepting the look and the biological processes which occur when terrestrial materials break down in our tanks is a fundamental shift in thinking.

By studying and encouraging the growth of this diversity of organisms, and creating a multi-faceted microcosm of life in our tanks, I believe that we are contributing to an exciting progression of the art and science of aquarium keeping!

Stay enthused. Stay excited. Stay thoughtful. Stay diligent. Stay relentless...

And Stay Wet.

Scott Fellman

Tannin Aquatics