"A most interesting mixture..."

We speak very often about the flooded forests of South America and elsewhere when discussing unique ecological niches in which terrestrial materials, such as botanicals, roots, branches, leaves, and soil play a role in shaping the aquatic ecosystem which arises following the inundation.

The mix of materials which comprise these unique habitats has defnitely been an inspiration for me to create quite a few different aquariums over the years! There is so much we can learn from studying these systems that we can apply in our hobby work!

To show you how geeky I am about this stuff, I have spent hours pouring over pics and video screen shots of some of these igapo habitats over the years, and literally counted the number of leaves versus other botanical items in the shots, to get a sort of  leaf to botanical "ratio" that is common in these systems. Although different areas would obviously vary, based on the pics I've "analyzed", it works out to about 70% leaves to 30% "other botanical items." 

The trees-or their parts- literally bring new life to the waters. Some are present when the waters begin rising. Others continue to arrive after the area is flooded, falling off of forests trees or tumbling down from the "banks" of the stream by wind or rain.

Terrestrial trees also play a role in removing, utilizing, and returning nutrients to the aquatic habitat. They remove some nutrient from the submerged soils, and return some in the form of leaf drop. 

Interestingly, studies show that about 70% of the leaf drop from the surrounding trees in the igapo habitats occurs when the area is submerged, but the bulk of it is shedded at the end of the inundation period. The falling leaves gradually decompose and become part of the detritus in the food web, which is essential for many species of fishes. This "late-inundation leaf drop" also sets things up for the "next round" - providing a "starter" of nutrients !

A most interesting mixture, right?

The materials that comprise the tree are known in ecology as "allochthonous material"-  something imported into an 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 includes leaves, fruits and seed pods that fall or are washed into the water along with the branches and trunks that topple into the stream.  

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 the aforementioned 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.

Yeah, the detritus forms not only a part of the food chain in these systems- it's a literal physical structure that provides an area for fishes to forage, hide, and in some instances, spawn among.

Everything working together. 

Many other fishes which reside in these flooded forest areas feed mainly on insects; specifically, small ones, such as beetles, spiders, and ants from the forest canopy. These insects are likely dislodged from the overhanging trees by wind and rain, and the opportunistic fishes are always ready for a quick meal!

 

Interestingly, it's been postulated that the reason the Amazon has so many small fishes is that they evolved as a response to the opportunities to feed on insects served up by the flooded forests in which they reside! The little guys do a better job at eating small insects which fall into the water than the larger, clumsier guys who are more adapted to snapping up nuts and fruits with their big, gnarly mouths! 

And yes, some species of fishes specialize in detritus.

As we have discussed more times than you likely care to remember, decomposing leaves are the basis of the food chain, and the they produce forms an extremely important part of the food chain for many, many species of fishes. Some have even adapted morphologically to feed on detritus produced in these habitats, by developing bristle-like teeth to remove it from branches,tree trunks, plant stems, and leaf litter beds. 

Of course, it's not just the fishes which derive benefits from the terrestrial materials which find their way into the water. Bacteria, fungi, and algae also act upon the nutrients released into the water by the decomposing organic material from these plants. Plants (known collectively to science as macrophytes) grow in or near water and are either emergent, submergent, or floating, and play a role in "filtering" these flooded habitats in nature.

Many, like the plants in the pic below, are simply terrestrial grasses which have adapted to survival under water for extended periods of time. This adds to the diversity of materials- both living ad dead- in these compelling habitats.

A most interesting mixture, indeed.

A most compelling model. A most fascinating example of a "functionally aesthetic" environment that you can duplicate in your home aquarium. Think about the environment, its external influences, the conditions, and the life forms that make use of it the next time you're conjuring up ideas for a new tank...It just might help you create one of the most amazing aquariums you've ever built!

Stay inspired. Stay curious. Stay excited. Stay observant...

And Stay Wet.

 

Scott Fellman

Tannin Aquatics  


Scott Fellman
Scott Fellman

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