August 15, 2017

Oh, what a tasty web...

If you read "The Tint" often, you know that we're really obsessed with creating really realistically functioning aquatic systems. Yes, we love natural-looking aquarium habitats, but we're equally as fascinated by replicated, or at least embracing, some of the functions which take place in the natural habitats from which our fishes come.

One of the things that we're fascinated by are what are known as "food webs."

A good description of an aquatic food web is: "...complex groups of organisms that perform different functions in the ecosystem. Phytoplankton are small primary producers suspended in water. They use nutrients along with carbon dioxide to harness sunlight energy and create biomass through the process of photosynthesis." (Source- Wikipedia)

In freshwater and many brackish ecosystems, one of the sources of "fuel" for aquatic ecosystems is leaves. As leaves drop into the water, they become food for a wide range of aquatic organisms, such as bacteria, fungi, crustaceans, and other microorganisms which act upon them to decompose them.

And in turn, fishes feed on many of these organisms. In fact, fungi are the key to the food chain in many tropical stream ecosystems. The relatively abundant detritus produced by the leaf litter is a very important part of the tropical stream food web.

Interestingly, some research has suggested that the decomposition of leaf litter in igapo forests is facilitated by terrestrial insects during the "dry phase", and that the periodic flooding of this habitat actually slows down the decomposition of the leaf litter (relatively speaking) because of the periodic elimination of these insects during the inundation. And, many of the organisms which survive the inundation feed off of the detritus and use the leaf substratum for shelter instead of directly feeding on it, further slowing down the decomposition.

As touched on above, much of the important input of nutrients into these habitats consists of the leaf litter and of the fungi that decompose this litter, so the bulk of the fauna found there is concentrated in accumulations of submerged litter. And the nutrients that are released into the water as a result of the decomposition of this leaf litter do not "go into solution" in the water, but are tied up throughout in the food web of the aquatic organisms which reside in these habitats.

In some streams, there is very little internal production of food sources for their resident fishes. Rather the food sources come from materials such as plants, fruits, leaves, and pieces of wood which come from the surrounding environment. Oh, and insects. Lots of insects from the surrounding trees and bank, which fall into the water. These are known as "allochthonous inputs" in ecology- materials imported into an ecosystem from outside of it. We've touched on this idea in a recent post.

As we touched on briefly, materials such as detritus comprise a very important part of the diet of many fishes in regions such as the Amazon. Yes, detritus, the oft-vilified "enemy" of the "clean" aquarium, in many aquarists' eyes, is pretty important stuff. Think about that the next time you reach for the siphon hose!

Now, how does all of this come together in the closed environment of the aquarium? Well, for one thing, the fungal and microbial communities which arise in our systems are likely far less dense than those in the wild habitats, where the resources are substantially greater. That being said, relative to a typical aquarium which doesn't have materials like leaves and botanicals to provide sustenance for these organisms, the botanical-style blackwater aquarium is a rich system!

With an abundance of leaves, would it not make sense that you'd see some emergence of microbial and fungal populations, functioning to some extent as they do in nature? The allochthonous inputs from our fish-feeding activities would certainly contribute to this "web", wouldn't they? And since we have the capability to impact the "productivity" of our systems based on external food inputs and the addition (or removal) of botanical materials, it seems to me that we could at least partially recreate the "food webs" associated with the systems we are trying to replicate.

Now, my plea to the industry yet again would be to develop pure cultures of some of the organisms found in these habitats, which would not only function as food for the fishes, but, if added to the aquarium well in advance of the fishes which might prey upon them, would be able to function as they do in nature, processing fungal and microbial growth and even detritus which occur among the leaf litter. We have bottled cultures of many saltwater copepods and such. They have become "staples" of the reef aquarium hobby for years.

(Some marine copepod products from Essential Live Feeds- one of my fave brands)

Would it not make sense for some enterprising manufacturer to develop and market these organisms for analogous purposes in the vastly larger freshwater market? I suppose it's like many other things- we need to get hobbyists to understand why they would want this stuff in their tanks! Hmm, that reminds me of what we had to do for a while when we established Tannin...!

Obscure and self-centered request notwithstanding, I really do think we'd be well-served to introduce some of the organisms (such as Gammarus, Daphnia, Bloodworms, even "Black Worms" or Tubifex) into our tanks for the sole purpose of attempting to develop at least part of a "food web." I mean, sure, it's not that simple, but to at least attempt this is a quantum leap over what has been done in this area in the past in freshwater systems (read that- essentially NOTHING!), and may at least give us some firsthand experience and insight into how these organisms can benefit our aquariums over the long term.

Now, in order to establish these organisms, you'd have to engage in the ridiculously patience-challenging practice of adding them to your tank months in advance of the fishes, to give them a chance to establish more stable populations that can resist the predation caused by the introduction of a large number of fishes. Think of the potential rewards for your patience, however!

Or, there is always the alternative of creating a "refugium" of sorts, with resident populations of these organisms safely tucked away from the main display tank, performing their leaf litter breakdown processes undeterred by the presence of hungry predators! This is something we've done in the reef aquarium world for decades, and to my considerable dismay, the idea never seemed to catch on in the freshwater world to any great extent. And of course, one of the thought processes behind the refugium idea is that an occasional careless organism will get sucked into an intake and be deposited into the display, providing a tasty treat for the resident fishes!

(My friend Marc maintains a pretty cool macroalgae-based 'fuge on his amazing reef aquarium...)

I firmly believe that the idea of embracing the construction (or nurturing) of a "food web" within our aquariums goes hand-in-hand with the concept of the botanical-style, blackwater (and brackish!) aquarium. With the abundance of leaves and other botanical materials to "fuel" the fungal and microbial growth, and the diligent husbandry and intellectual curiosity of the typical "tinter", the practical execution of such a concept is not too difficult to create. We are truly positioned well to explore and further develop the concept of a "food web" in our own systems, and the potential benefits are enticing!

I hope that I've at least whetted your appetite (ewww!) for the idea with this rather cursory and choppy introduction into the concept of food webs in the aquarium!

Stay intrigued. Stay engaged. Stay inspired. Stay on this!

And Stay Wet.

Scott Fellman

Tannin Aquatics