The "why's and hows" of mangrove wood in the brackish water/botanical-style approach...

Yes, it's Summer, we're out doing other stuff, and we're really a couple of months away from prime "aquarium season", yet it's always a good idea to start thinking about some of the cool projects we want to play with during the upcoming cooler months of Fall. And, if you're looking for something new to play with when you head back indoors, may we suggest a brackish water aquarium? Or, our version of a brackish-water aquarium?

Our vision of a brackish water aquarium utilizes many elements common to other aquascaping approaches and aquarium environmental management methods. Although we are taking a sort of different route and philosophy in regards to the functionality (mainly, creating a rather "rich system" from an ecological standpoint), the concept is not that much different from what we've been working with in blackwater. It's just that greater emphasis is placed on the specific components in the system.

One of the most obvious differences (besides the salt, of course!) is the use of a different type of wood than we're used to. We utilize the branches and roots of the Red Mangrove tree (Rhizophora mangle), because, well- they're the "real deal", and we have a legally-collected source for them. 

Mangrove wood imparts many of the same properties to the water as any other type of wood used in aquarium setups. It will slowly release tannins, which may tint the water, and recruit biofilms and algae. The main difference between our approach to utilize mangrove versus any other wood is that it looks like the real thing because it IS the real thing.

And the actual mangrove wood is different than wood or branched from other trees that might be used in aquarium work. For one thing, it's structurally different. Red Mangroves prop themselves above the water level with stilt roots and can then absorb air through pores in their bark. Red mangroves eliminate salt through very impermeable roots which incorporate a waxy substance called suberin. Its main function is as a barrier to movement of water and soluble substances within the tree itself. In the case of the Mangrove, the suberin is used as a sort of filtration mechanism to export sodium salts from the rest of the tree. It's really efficient, too. Scientists have discovered that up to 97% of the salt has been removed from the tree via the root! This is very special wood!

Mangroves grow in muddy substrates which have little free oxygen available. Anerobic bacteria present in these substrates liberate nitrogen and other compounds that are present, leaving it rather devoid of many substances plants need for growth.  The aerial roots of mangrove trees (known as "pneumatophores", allow then to absorb gasses directly from the atmosphere, and to derive some nutrition from the relatively non-nutritious soil. These trees are also able to store atmospheric gasses within the roots, processing them at all times (submerged or not).

These are extremely adaptable trees, and are thought to be major buffers against the tidal actions of cyclones, tsunamis, and other storms. They foster a diversity of animal life, and for the basis for a unique and fascinating habitat.

With so much usefulness it's hardly surprising that these are highly valued in many parts of the word, and are, indeed, protected in many of them. In fact, you might ask how we in all good conscience can offer the wood for sale! The answer is as surprising as it is legitimate. The only reason we are able to legally offer this wood is because our source is from the State of Hawaii, where the local government has declared the species to be "highly invasive", damaging the local ecosystem, and extensive eradication efforts are continuous. Red mangroves in Hawaii have been found to grow to higher densities than in their native range, because Hawaii lacks the species that attack the flowers and propagules. They grow uncontested; out of control, causing problems for the local flora and fauna. Removal is important.

And it's not just the growth that's problematic- it's the leaves they drop. Beneficial in ecosystems that are "equipped" by nature to accommodate it, the leaves are extremely problematic in Hawaii. The amount of "litter-fall" from mangrove stands at Nu‘upia Pond, Oahu, for example, has been measured at levels which exceed the "net primary productivity"  of the Red Mangrove tree in its native range in Florida  These added organic inputs have led to detrital accumulations and algal blooms in Hawaiian waters, negatively impacting aquatic life.

Surprising, huh?

The local authorities and the U.S. Department of Agriculture are happy to see us take them off of their hands! So, in a strange twist of irony, you're actually helping the local Hawaiian ecosystem and the government to a certain extent by purchasing this mangrove wood from us. And, as an added bonus, you're utilizing the branches and roots- which would otherwise be chain-sawed down and burned- for aquarium decoration, sparing the need to use other methods to dispose of the material. And you could argue that gas-powered chain-saws, and bulldozers and burning them releases carbons into the atmosphere which can contribute to global warming, etc., so I suppose one could make a (weak) argument that taking a tiny, tiny fraction of them for aquarium use is sort of doing something to combat this!

Yup, strangely ironic, regardless, right?

So how do you use mangrove wood in the aquarium? Well, really, just like any other type of wood, really.  Preparation is just like any other wood we all use. The main differences when using mangrove are the context and the physical orientation. The context being, we're using them in an aquarium that has a specific gravity of around 1.003-1.005, and that we're okay with it releasing some tannins into the water and creating some tint. It's as much an "environmental enrichment vehicle" as it is an aquascaping "prop" for us. It beautifully replicates the look of the habitat, while providing some functional benefits (i.e.; a substrate for organisms, plants and algae to attach to and hide amongst).

From an "orientation" standpoint, to get maximum functionality and realism out of the wood, you would be best served to orient it vertically in the aquarium, as opposed to horizontally or in some other configuration as we do with other wood. In particular, the mangrove branches that we offer are essentially identical to the appearance of the prop roots that project downwards from the mangrove trees into the water. By orienting the branches this way, and supplementing them with the thicker, more gnarled mangrove root pieces, you'll end up with an incredibly realistic-looking simulation!

Now, I suppose it's fair to question the idea of "function" when we're talking about dead wood pieces, as opposed to the living tree. Of course, the wood will not perform any nutrient export (any more than other types of aquatic wood does in any type of aquascape) or exchange salts, etc. The point here is that when we incorporate the wood into a brackish-water aquarium with a rich substrate (the other component of our brackish approach, which we'll delve into some other time), and some mangrove leaf litter, we're replicating the aesthetics and at least part of the function of the mangrove root habitat. In our opinion, it's a far more realistic and functional approach than the typical "rocks/white sand/seashell" approach than has been the typical "brackish" display tank for decades.

And, if you incorporate some live mangrove propagules and some adaptable aquatic plants (like our fave Cryptocoryne ciliata) into your display, you can have significant functionality (oxygen production/nutrient export from the plants), and the decomposing leaves and botnanicals can help foster, to some degree, a "food web" of microorganisms and macro fauna (snails, crabs, etc.) which can contribute to a more biologically-diverse closed ecosystem if managed properly.

This is sounding very much like our approach to blackwater/botanical-style aquariums, isn't it?


The idea of fostering a unique closed-system ecology and all of the challenges and benefits that can come with it is irresistible. And don't get me wrong- there will be challenges: We're talking about creating very rich, sediment-based substrates with a lot of leaf litter and some plants in a brackish water environment.

A lot of stuff going on here, right? On the surface, it seems like a recipe for trouble! I had many people telling me (without even trying this) over the years that it would be a total fail. They said "Too much bioload!" or "Your pH and alkalinity will be all over the place!" Or "Crash!" The reality is that, just like a blackwater, botanical-style system, it works really well if you use common sense husbandry techniques. Understanding bioload and utilizing the benefits of nutrient export via plant growth, denitrification, and water exchanges are the keys here. I've never had a crash doing this. I've never had a crash with a blackwater-botanical-style system, either, nor have most of you.

It's about how you manage the system. It's about common sense, husbandry, and observation. And taking some risks. And figuring some stuff out along the way as we get into it more. "Crowd- sourced" exploration of new aquarium approaches is very exciting, because we all learn together. Sure, some of the basic "proof-of-concept" has been done before, but putting it all together, playing with some of the nuances and subtleties, and applying finesse to it all- evolving the aquarium-that's still going to be an ongoing thing. Mimicking some natural processes from a complex habitat in the confines of an aquarium will be very challenging!

We have a lot more to discuss/debate/postulate/explore over the coming months with "Estuary", as more and more hobbyists are starting to play with this stuff and the botanical/brackish approach.

It's wide open for experiments, projects, discoveries, failures, and yeah- breakthroughs. We simply need to loose the chains of "how we've always done it" and  "that can't work because..." and move forward boldly and with an open mind, understanding that there will be challenges whenever we forge into previously uncharted territory. It's not "plug-and-play", or without any possibilities of failure. But the potential is amazing. Hope you come along for the ride.

It's super cool! 

Hope we've whetted your appetite and ignited your curiosity just a bit.

Exciting stuff. Different, yet familiar in many ways. Always challenging. Always enjoyable.

Something you might want to play with in your fish room when the first chill of autumn hits. 

Stay excited. Stay curious. Stay realistic. Stay engaged.

And Stay Wet.


Scott Fellman

Tannin Aquatics




Scott Fellman
Scott Fellman


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