I'm obsessed with leaf litter in the wild and in the aquarium. I think it's because it's literally an oasis of life. Compelling, diverse, and productive.
Many tropical rivers and streams are characterized by large quantities of leaf litter and decaying botanicals on the bottom, with typically clear (but tinted) water. As discussed many times in this column, leaf litter is used as shelter, spawning ground, feeding area, and in some instances, as supplemental food itself. This is a highly productive habitat in nature that also just happens to look really cool in our aquariums, performing exactly the same function!
And fish population density is often correlated with the availability of food resources- and, as we've discussed many times here, leaf litter beds are highly productive food resources!
In wild habitats, there have been many instances where researchers have counted literally hundreds of fishes per square foot inhabiting the matrix of botanical materials on the bottom of stream beds, which consists primarily of leaf litter. As dead leaves are broken down by bacterial and fungal action, they develop biofilms and associated populations of microorganisms ("infusoria", etc.) that are an ideal food source for larval fishes.
When you take into account that blackwater environments typically have relatively small populations of planktonic organisms that fish can consume, it makes sense that the productive leaf litter zones are so attractive to fishes! That being said, leaf litter beds are most amicable to a diversity of life forms These life forms, both planktonic and insect, tend to feed off of the leaf litter itself, as well as fungi and bacteria present in them as they decompose.
The leaf litter bed is a surprisingly dynamic, and one might even say "rich" little benthic biotope, contained within the otherwise "impoverished" waters. And, as we've discussed before on these pages, it should come as no surprise that a large and surprisingly diverse assemblage of fishes make their homes within and closely adjacent to, these litter beds. These are little "food oasis" in areas otherwise relatively devoid of food.
The fishes are not there just to look at the pretty leaves!
Major rivers like the Rio Negro are often called "impoverished" by scientists, in terms of plankton production. They show little seasonal fluctuations in algal and bacterial populations. This is a fact borne out by many years of study by science. However, "impoverished" doesn't mean "devoid" of life. And in many cases, these populations of food organisms do vary from time to time- and the fish along with them.
Other blackwater systems do show seasonal fluctuations, such as lakes and watercourses enriched with overflow in spring months. At low water levels, the nutrients and population of these life forms are generally more dense.
Creatures like hydracarines (mites), insects, like chironomids (hello, blood worms!), and copepods, like Daphnia, are the dominant fauna that fishes tend to feed on in these waters. This is interesting to contemplate when we consider what to feed our fishes in aquariums, isn't it?
There's a lot of food out there, for the fishes willing to look for it...which, pretty much all of them devote most of their lives to doing, lol
It's not really that much different in the aquarium, is it? I mean, as the leaves and botanicals break down, they are acted upon by fungi and bacteria, the degree of which is dependent upon the available food sources. Granted, with fishes in a closer proximity and higher density than in many wild systems, the natural food sources are not sufficient to be the primary source of food for our fishes- but they are one hell of a supplement, right?
That's why, in a botanical-rich, leaf litter dominated aquarium, you see the fishes spending a lot of time foraging in and among the litter...just like in nature.
There is something oddly compelling to us when we look at both aquariums and natural biotopes with a diverse, interesting botanical structure. You set the stage with wood, plants, and then enhance it even more with botanical materials.
Nature does the rest.
The fishes will follow.
Stay engaged. Stay excited. Stay focused. Stay patient...
And Stay Wet.