May 20, 2019

Just add water...literally.

In the jungles and rain forests of the world, streams and floodwaters meander through. In regions such as The Amazon, this has become an integral part of the ecosystem.

As these waters work their way through the soils, fallen trees, accumulated leaves, branches, and seed pods, the water absorbs tannins, humic substances, dissolved organics, and other compounds which contribute to the now aquatic environment...

We know this. These are dynamic, interdependent habitats.

These terrestrial habitats are "seasonally inundated" by the significant rainfall common to this region; some of these forest floors may be submerged for almost half a year...that's a LOT of water! Like, 3%-4% of the water in the Amazon Basin at any given time...And these are precious, diverse natural treasures, so replicating one in the home aquarium is another way to learn and teach more about them, isn't it?

Igapo forests have a pretty significant amount of trees; one study found that over 30 species of trees are found in these areas, creating coverage of something on the order of 30%, and are known to have soils that are acidic in nature, yet low in nutrient content (because they don't receive a seasonal influx of nutrients like regions called "varzea", which are flooded by sediment-laden "whitewater" rivers).

The water depth can vary from as little as 6-8 inches ( 15.24cm- 20.32cm), to almost 20 feet (6.96m)! This influx and egress of water can happen fairly rapidly. And of course, as a result of the materials the waters flow through, they have a lot of tannin and humic substances in them from all of that soil and plant materials.

As aquarists, this dynamic environment is incredibly inspiring! The "igapo" habitat can really help you flex your creative muscles, offering the dual challenge of creating something unique, while holding back and not going too crazy with tons of detail. Rather, a fewer, stronger elements, punctuated with some smaller details provided by the botanicals, can create an engaging, mysterious, and inspiring display!

As we've discussed before, Amazonian leaf litter beds are home to a surprising variety and population density of fishes, with some studies of igapos yielding as many as 20-40 different species of fishes in a 200 square meter area! And, the majority of the specimens found in these studies are small, averaging around 40mm-100mm (1.5"- 3.9") in length!

This is interesting from an aquarist's perspective, because we can create a pretty dynamic and interesting environment, with lots of cool small fishes, if considerations are made for tank size, filtration and husbandry.

The trees-or their branches and leaves-once submerged- literally bring new life to the waters. The materials that comprise the tree are known in ecology as "allochthonous material"- something imported into an aquatic ecosystem from outside of it. (extra points if you can pronounce the word on the first try...) And of course, in the case of trees, this also includes fruits and seed pods that fall or are washed into the water along with the branches and trunks that topple during inundation.

These materials are known to ecologists as “coarse particulate organic matter”, and in the waters of these inundated forest floors there is a lot of CPOM, and the community of aquatic organisms (typically aquatic insects and crustaceans) has a high proportion of “shredders”, which feed on the CPOM and break it up into tinier bits called (wait for it...) "fine particulate organic matter."

Some of these "shredders" and their larvae are a direct source of food for fishes, providing a nutritious food source for growing populations in these waters.

And of course, some fishes directly consume fallen fruits and seeds themselves as part of their diet as well, aiding in the "refinement" of the CPOM. Think about the Pacu, for example, which has specialized mouthparts suited to crushing hard-shelled fruits and seeds. Other organisms make use of the fine particulate matter by filtering it from the water or accessing it in the sediments that result. These allochthonous materials support a diverse food chain that's almost entirely based on our old friend, detritus!

Yes, detritus. Sworn enemy of the traditional aquarium hobby...misunderstood bearer of life to the aquatic habitat.

There's a lot going on here, huh?

And, although the forest floor receives substantially less sunlight than open rivers, the nutrients and available light are utilized by algae, which may colonize the surfaces facing up into the sun. True aquatic plants are essentially non-existent in the flooded forests. Rather, the presence of terrestrial grasses and plants, which can tolerate periods of submersion, are the most common plants here.

And of course, branches, bark, and ultimately, the tree itself, will gradually decompose over long periods of time. Hollowed-out sections will be inhabited by fishes and exploited for the shelter they offer. Other fishes utilize these "microhabitats" as spawning areas, and provide defensible spaces to rear their fry.

And interestingly, when you think about it, fish movement, species "richness," and the size of the fish population are affected by the physical and biological influences of fallen trees! How interesting that the lives of aquatic animals are so inexorably linked to the terrestrial environment!

And the deep beds of leaves and plant parts that may be "corralled" by fallen trees- a sort of natural "dam"- will affect the types of fishes which reside there. Some fish species, which cannot tolerate the lower oxygen concentrations found in these areas of deep leaf litter, will reside elsewhere, allowing a sort of natural "resource partitioning" that lets more tolerant species (such as knifefishes, catfishes, etc.) take advantage of the food sources in these deep beds.

Other fishes take advantage of the physical barrier that a fallen tree presents to shelter from predatory species. Numerous behavioral and even physiological adaptations have taken place over eons to allow fishes to exploit these changes in their environment caused by fallen trees!

It's pretty fascinating stuff. You could literally spend a lifetime studying, replicating, and learning from these habitats, and never run out of new ideas or inspiration...They're constantly emerging, changing, and evolving.

And it's all part of the reason that I spend so damn much time pleading with you- my fellow fish geeks- to study, admire, and ultimately replicate natural aquatic habitats as much as you do the big aquascaping contest winners' works. In fact, if every hobbyist spent just a little time studying some of these unique natural habitats, I think the hobby would be radically different.

Time for a change, isn't it?

Stay inspired. Stay creative. Stay curious. Stay diligent...

And Stay Wet.

Scott Fellman

Tannin Aquatics