February 27, 2020

More love for Mangroves...

Yeah, time to talk about that salty stuff again...

When we launched "Estuary by Tannin Aquatics", our foray into the "botanical-style brackish aquarium", it was driven by an obsession with the functional and aesthetic aspects of this unique ecosystem. With a heavy emphasis on substrate, decomposition, and all of the good stuff that us "Tinters" seem to love, this more "honest" interpretation of the brackish water aquarium is proving irresistible to many of you!

It's something we're all sort of familiar with- yet it's all kind of new.

And it's starting to catch on...

Of course, when we are talking about brackish aquariums, we'd be completely remiss if we didn't mention the "stars" of this habitat, the Mangrove trees! In our practice , we'll focus on the readily available, reasonably hardy "Red Mangrove", Rhizophora mangle.

Hardly what you'd call an "aquarium plant"- I mean it's a tree.

That being said, the Mangrove is an amazing tree that certainly has applications for aquariums- specifically, brackish aquariums. Now, without going into a long, long, recap of what mangroves are and how they function (You can Google this stuff and get hundreds of hits with more information than you could ever want), let's just say that mangroves are a group of trees and shrubs which live in the coastal intertidal zone, in areas of warm, muddy, and salty conditions that would simply kill most plants.

They possess specialized organs within their branches, roots, and leaves which allow them to filter out sodium, absorb atmospheric air through their bark, and generally dominate their habitats because of these and other remarkable adaptations.

There are about 100-plus different species, all of which are found between tropical and subtropical latitudes near the equator, as they are intolerant of cold temperatures. Mangroves put down extensive "prop roots" into the mud and silt in which they grow, giving them the appearance of "walking on water." These root tangles help them withstand the daily rising/falling tides, and slow the movement of the water, allowing sediments to settle out and build up the bottom contours of the local ecosystem.

And of course, the intricate root system not only protects coastlines from erosion, it plays host to a huge variety of organisms, from oysters to fungi to bacteria to fishes. The fishes use mangrove habitats as a feeding ground, nursery area, and a place to shelter from predators.

Okay, you get it. But how do we use these trees in the aquarium. And wait a minute, you're talking about a tree? WTF?

I have no illusions about using live Mangrove plants (available as "propagules") to serve as "nutrient export" mechanisms as they do in nature. You've seen this touted in the hobby over the years, and it's kind of silly, if you ask me. They just grow too damn slow and achieve sizes far beyond anything we could ever hope to accommodate in our home aquarium displays as full-grown plants with large-scale nutrient export capabilities. We've played with this idea in saltwater tanks for decades and it's really more of a novelty than a legit impactful nutrient export mechanism.

Mangroves can and will, however, reach a couple of feet or so in an aquarium over a number of years, and they may be "pruned" to some extent to keep them at a "manageable" size, similar to a "bonsai" in some respects.

Oh, and before you start going off on me about their unsuitability for aquariums or some ethical implications for their "removal" from the wild, let's talk for a second about how we acquire them and how they grow. First off, removing a growing mangrove tree or seedling from the natural environment is damaging, unethical, illegal in most areas, and essentially idiotic.

NO one should even consider doing that. Period. Propagules are readily, legally available, easy to sprout, and should be utilized by any hobbyist who is contemplating playing with these trees.

And of course, part of the attraction of mangroves is the biome in which they occur.

Mangrove communities tend to accumulate nutrients, such as nitrogen and phosphorus, as well as some heavy metals and trace elements which become deposited into estuarine waters from terrestrial sources. These communities become sort of "nutrient sinks” for these materials.

And of course, Nature has a plan for this stuff: Mangrove roots, and the epiphytic algae often found on and among them, as well as bacteria, microorganisms, and a wide variety of invertebrates that reside there, take up and store the nutrients in their tissues.

Mangroves also function as continuous sources of carbon, nitrogen, and other elements, as their living material (i.e.; leaves and epiphytic organisms and plants) die and are decomposed. Tidal flushing assists in distributing this material to areas where other organisms may utilize it.

And here's the other cool thing:

Leaf litter is extremely important in a Mangrove ecosystem! Other materials, including twigs, branches, and other botanical items, is a major nutrient source to many creatures which function as "consumers" in these ecosystems. A study conducted in the 1970's by Pool et al, showed that the leaf litter in brackish Mangrove ecosystems is composed of "...approximately 68 – 86 % leaves, 3 – 15 % twigs, and 8 – 21 % "miscellaneous" material."

Thanks for the leaf litter "recipe", scientist friends! I mean, could we ask for more?

Now, let's be clear- Mangroves are different types of leaves than we are currently using in our blackwater tanks, but the concept is entirely familiar to us, right? (Oh, and by the way, it's totally okay to use mangrove leaves in your freshwater botanical-style blackwater aquarium!)

Once fallen, leaves and twigs decompose fairly rapidly in these habitats. As you might imagine, areas which have high tidal flushing rates, or which are flooded frequently, have faster rates of decomposition and export than other areas. Studies also found that decomposition of red mangrove litter proceeds faster under brackish conditions than under fresh water conditions.

Oh, and as the researchers so eloquently stated, some of these habitats have "brownish-colored water, resulting from organic matter leaching from the mangroves."

Algal growth, biofilms, brown water...at 1.005 specific gravity. Does it get any better?

So, let's think of this for just a minute, in terms of "that thing we do"- botanical-style aquariums. Just change up the "media" from "blackwater" to "brackish water", with a specific gravity of 1.005-1.010. We collectively as a community have a lot of experience managing higher-nutrient blackwater botanical systems, containing large numbers of leaves and other botanicals, right? Can this experience be applied to the brackish game?

Of course it can!

Like our "conventional" (Shit, that's funny to say, huh?) botanical-style systems, the brackish system embraces the same use of decomposing leaves, wood, and botanicals, with the added variables of a rich, "sediment-centric" substrate and the dynamic of specific gravity to contend with.

Interestingly, however, this type of system runs much like the blackwater, botanical-style systems that we are used to, with the exception that it is far more "nutrient rich" than the blackwater tanks. The dynamics of decomposition and the ephemeral nature of leaves and such in the water are analogous in many respects, as well.

Fungi and bacteria in brackish and saltwater mangrove ecosystems help facilitate the decomposition of mangrove material, just like in their pure freshwater counterparts. Interestingly, in scientific surveys, it's been determined that bacterial counts are generally higher on attached mangrove leaves than they are on freshly-fallen leaf litter, and this is kind of interesting, because ecologists feel that attached, undamaged mangroves leaves don't release much tannin, which, as we know might have some "anti-bacterial" properties. However, it's also been found that materials like humic acid, which are abundant in the mangroves, stimulate phytoplankton growth there.

Interesting, right?

Well, to me it is, lol.

The leaves of mangroves, as they break down, become subject to both leaching of the compounds in their tissues, as well as microbial breakdown. Compounds like potassium and carbohydrates are commonly leached quickly, followed by...tannins! Fungi are the "first responders" to leaf drop in mangrove communities, followed by bacteria, which serve to break down the leaves further.

So, in summary, you have a very active microbial community in a brackish water aquarium!

And yeah, the water in a brackish system "configured" in this manner is decidedly tinted- largely a function of the mangrove branches and roots, which, as they break down, release a significant amount of color-producing tannins from their tissues.

It's hardly a secret that mangrove wood, leaves, and bark are loaded with these tannins! In fact, Red Mangrove bark is one of our favorite "secret weapons" for producing incredibly deep tint in all types of botanical-style aquariums!

Now, the management of a botanical-style brackish tank is really surprisingly similar to that of a typical blackwater aquarium. The biggest difference is the salt and perhaps a greater interest in a deep, very rich substrate. Now, one parameter I changed since the system began was to increase the specific gravity from 1.004 to 1.010 This was done because it is a sort of "sweet spot" that many of the fishes which I am interested in (gobies, rainbow fishes, chromides, mollies, etc.) seem to fare quite well at this slightly higher S.G.

Also, I've made no secret about a desire at some future point to do a brackish system where I slowly push things all the way up to like 1.021 (on the low end of natural seawater specific gravity) and incorporate corals and macro algae into the display, along with marine fishes! And, if I do execute this, the "creep" towards this higher S.G. will be made over a very long period of time (close to a year), so it will be advantageous for the resident fishes to adapt to full-strength marine water slowly.

So, yeah, you're playing with salt...And, small concentrations of salt. Accuracy in measurement is essential.

HOT TIP: Get a digital refractometer. Pay real money and don't get a piece of shit toy. Consider it an essential tool to your hobby that you'd be foolish not to own.

Do it. You won't regret it at all. Seriously.

And sure, managing a system that "floats" between two realms (freshwater and marine) seems like a bit of a balancing act, I know..because it is. However, it's not difficult. You simply apply the lessons you've learned playing with all of this crazy botanical-style blackwater stuff we talk about all the time.

Yes, you might kill some stuff, because you may not be used to managing a higher-nutrient brackish water system. You have a number of variables, ranging from the specific gravity to the bioload, to take into consideration. Your skills will be challenged, but the lessons learned in the blackwater, botanical-style aquariums that we're more familiar with will provide you a huge "experience base" that will assist you in navigating the "tinted" brackish water, botanical-style aquarium.

Now, this IS a different type of approach to brackish aquariums.

However, it's likely not "ground-breaking", in that it's never, ever before been done like this before.

I just don't think that t's never been embraced like this before: Met head-on for what it is- what it can be, instead of how we wanted to make it (bright white sand, crystal-clear water, and a few light-colored rocks and seashells...A perfect example of Nature "edited" to our aesthetic "standards"). Rather, it's an evolution- a step forward out of the artificially-induced restraints of "this is how it's always been done"- another exploration into what the natural environment is REALLY like- and understanding, embracing and appreciating its aesthetics, functionality, and richness.

In my opinion, the key to our "evolved" brackish-water aquarium approach is looking at the substrate- and the other materials which accumulate on the bottom of the aquarium- as an essential and highly important component of the system.

The bottom of this type of habitat is covered with a thin layer of mangrove leaf litter- and of course, that's part of the attraction here! This will not only provide an aesthetically interesting substrate- it will offer functional benefits as well- imparting minerals, trace elements, and organic acids to the water.

Mangrove leaf litter, like its freshwater counterpart, is the literal "base" for developing our brackish-water aquarium "food chain", from which microbial, fungal, and crustacean growth will benefit. And of course, these leaves will impart some tannins into the water, just as any of our other leaves will!

And you can play with many different types of substrate materials, ranging from sand to mud and everything in between. The richer the better, as far as I'm concerned.

Again, a different approach, fro ma different angle.

The biggest headache. Fishes.

And of course, no brackish water aquarium is complete without brackish-water fishes...And traditionally, that has been a bit of a challenge, in terms of finding some "different" fishes than we've previously associated with brackish aquariums. I think that this will continue to be a bit of a challenge, because some of the fishes that we want are still elusive in the hobby.

New brackish-water fishes will become more readily available when the market demand is there. In the mean time, we can focus on some of the cool fishes from these habitats which are currently available to us.

I think that the key, as always- is more and more hobbyists getting involved in this unique hobby specialty area.

I'm proud to have pushed this type of approach, and even prouder that many of you have been inspired to try it as well! Keep pushing outwards. Keep trying new approaches to things that might have been a bit "under-served" in years past...

Our work is cut out for us in the brackish world, for sure.

Yet, this is so damn fun.

Stay fascinated. Stay bold. Stay diligent. Stay creative. Stay observant...

And Stay Wet.

Scott Fellman

Tannin Aquatics