"The detritus dilemma?"

Some six months into my brackish water mangrove aquarium, and I'm starting to achieve many of the results that I was hoping to. This was a tank assembled to demonstrate as visibly as possible that the more "traditional" hobby concept of a brackish water aquarium was sort of- well, dull and boring. Grey, white, and not particularly interesting. 

Yeah, it was my stated goal to change this unfortunate perception!

I decided to demonstrate that the botanical-style approach which we have used so successfully in our blackwater aquariums is every bit as applicable and can be every bit as dynamic, interesting, and successful with brackish! It involved incorporating many of the ideas we've played with for some time in our blackwater tanks, and perhaps taking it a bit further, with the inclusion of mangrove propagules as the living "stars" of the display. As we've discussed previously in this blog, mangroves are amazing plants which are an integral part of a highly dynamic and complex ecosystem.

One of the first decisions I made with this aquarium was to NOT siphon out the "organic debris/detritus" (total "catch-all" phrase, huh?) that accumulate during the normal course of existence of any aquarium. My rationale was that, the bulk of this material was fish waste and broken down leaves and botanicals, as opposed to uneaten food and such. My whole point of the brackish water Mangrove aquarium "exercise " was to create a simulation of the organic-heavy, exceedingly rich substrates in which they are found, while still creating a manageable closed system that didn't turn into a sewer!

I kind of figured that I don't overfeed. I don't over-stock, and I perform regular water exchanges on a weekly basis. I employ practices which assure as much environmental consistency as possible. And yeah, the physical environment has a very slight amount of fine organic debris/detritus on the substate. I've purposely siphoned the stuff out before, and by crude estimation, I'd say that well over 80% of what there actually is there, accumulating on the substrate, is the aforementioned botanicals and leaves In a decomposed state. A sort of "mulch", if you will. I do see Nerites snails and some fo the fishes foraging in this material from time to time... but it's not all that noticeable unless you look really carefully.

I think these replicate, to some extent, the types of rich substrates in which mangroves grow and thrive. If you recall from my previous ramblings about this tank, we decided to utilize a variety of fairly rich substrate materials, including some commercial "marine biodsediment" additives, aquatic plant soil, sand, and a fracted clay gravel for the "top-dressing.

The reason for this section of "rich" substrate materials was twofold:

First, I wanted to create a functional mud-like substrate that would facilitate both denitrification and the ability to  provide a habitat for minute life forms. I felt that this would also be a more natural setting for a brackish water aquarium. My original intent was to plant some Cryptocoryne ciliata, a species well-known for its ability to adapt to a low salinity brackish-water environment. This plan was ultimately abandoned when I decided to increase the specific gravity of the aquarium to 1.010, considerably higher than the documented SG at which this plant is known to survive (typically 1.002-1.005).

The second reason for employing such a rich substrate in a "non-planted"  aquarium such as this was to set up the system for the point when the mangrove propagules, which I anchored to the upper part of a dead mangrove root/branch "structure", would put down prop roots and ultimately touch down and penetrate the substrate layer. I knew this process would take many months, of course, given the depth of the tank.

I also added some dried Malaysian Yellow Mangrove leaves to the surface, with the intention of letting them do their thing and decompose on the substrate and "do their thing" to help enrich the habitat with tannins and humic substances. A crew of Olive Nerites snails was added to the system as a means to control the algae and "work over" the decomposing leaves, and they are remarkable for their ability to do both. 

So, what we have seen over the first six or so months of this aquarium's existence has been the development of a remarkably stable, biologically active, and rich habitat. The mangroves have done what we thought they'd do: Put down prop roots, and grow many leaves, some of which do dry up and fall...and of course, we do allow the leaves to accumulate on the bottom, just like in the natural habitat we are attempting to replicate to a certain extent.

Mangrove ecosystems are remarkably complex, diverse systems which process nutrients by decomposing and utilizing organic matter. Many organisms, like fungi, bacteria- even sponges, work together to utilize the vast food resources produced in these habitats. And larger creatures, like crabs, amphipods, etc., break apart leaf bits, providing a "gross dismantling" service that contributes to decomposition of these materials, leading to detritus.

Now, in the confines of an aquarium, we can't likely keep every single type of life form that we'd encounter in wild mangrove habitats- but we can incorporate some of them to perform some of the same functions. I find this both challenging and compelling! Again, it's sort of that "functional aesthetics" thing...coupled with my ability to tolerate the brown water, decomposing leaves, etc. that are essential by-products of this environment.

In wild mangrove habitats  a significant amount of detritus is readily consumed by a group of detritivorous animals and fishes before it is being rematerialized completely in to inorganic nutrient form. And production and accumulation of detritus in these systems has been correlated by scientists to increased growth of the mangroves themselves.

Now, interestingly enough, as I've experienced with my blackwater, botanical-style aquariums, I've seen a remarkable stability in terms of the environmental parameters, and a definite sold growth in the mangrove seedlings, which has been especially impressive since the roots began "touching down" and penetrating into the substrate layer.

What I'm seeing- and what I planned on seeing- is the substrate playing a very important role in the overall setup...With the mangroves growing at a significant pace, laying down thicker and thicker root structures. I have been diligent about not overfeeding the tank, but I do little to no siphoning of the substrate. Even the nutrient-rich fecal pellets of the snails are allowed to accumulate...Yeah, this is a far, far different approach than I've ever taken with any aquarium!

And I'm okay with that.

Although it seems very weird simply stating, "I'm not siphoning the bottom of my aquarium and allowing the detritus produced by decomposing leaves and such to accumulate." - I have no particular feelings of negativity attributed to this practice. I'm quite okay with it, because it's a well-managed aquarium, with the other basics of aquarium husbandry attended to.

This is truly one of the most stable, easy-to-maintain systems I've ever kept. And really, everything has been remarkably predictable! The biggest surprise was the very rapid establishment of the mangroves- in particular, the robust development of the leaves.

Now, I attribute this to multiple factors: The depth of the aquarium, which forced the roots to grow downward significantly to establish themselves, the lighting, which I believe is excellent, and the environmental parameters, which are stable and well-suited for mangrove growth. And finally- certainly NOT the least important factor- is the rich substrate they encounter once the roots touched down. Allowing leaf drop and subsequent decomposition is mimicking exactly what happens in the natural environment. I believe that the lack of disturbance of the substrate has been and will be a continued factor in the overall "performance" of the system.

It's been a grand experiment, the tinted water and rich substrate...both of which have run somewhat contrary to the vision and execution of the majority of brackish water aquariums I've seen in the hobby in recent years. There is so much more to be learned from this aquarium over the long term...

Perhaps the best lesson is the confidence that you can gain from executing on an idea- no matter how unconventional it might seem- if you have a fairly solid understanding of what to expect. The mangrove habitat is surprisingly well studied by science, and there is a ton of research literature out their on the ecology of these unique plants and the role that they play in their habitats. And of course, a lot of information about the habitats themselves.

Why haven't we seen more brackish water aquariums that, well- look like brackish water ecosystems? Let alone, attempt to replicate some of their function? I think that it's an example of the aquarium hobby creating a stylized interpretation of this habitat for many years, as opposed to putting a bit of confidence I the environment itself and using that as an inspiration for an aquarium setup! A certain hesitancy about utilizing decomposing leaves and such in our aquariums.

Some three years in to our botanical-style aquarium "revolution", the global "tint" community is gaining confidence in utilizing leaves, botanicals, and other natural materials to not only achieve a certain look- but to replicate as much as possible the function of these impressive and alluring natural ecosystems.

We're learning that stuff like detritus is not necessarily a bad thing, and that letting it accumulate under the right circumstances shouldn't be cause  for a dilemma- particularly when it's affiliated with a closed ecosystem which an process and utilize it much I the way nature does I the mangrove estuaries of the tropical world...Something worth replicating, huh?

I think so. More on this topic in the future!

Stay bold. Stay studious. Stay curious. Stay resourceful. Stay diligent...

And Stay Wet.

 

Scott Fellman 

Tannin Aquatics 

 

 

 

 

 

 

 

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