November 13, 2019

The magnificent versatility of mangrove leaves...

As you know, for some strange reason, I tend to loathe the idea of writing adoring blog pieces on specific botanical materials that my company offers, because it feels kind of- well- crassly commercial...

However, the bigger picture here is not just to "push product." It's to further an idea- a concept, and to foster the growth of a movement which we hope has significant, lasting impact on the aquarium hobby in general.

In the botanical aquarium world, the work that we as a community have done, has actually made it easier on ourselves to create more naturally functioning aquariums. And, being able to select materials such as leaves for specific types of applications, habitat simulations or aesthetic/environmental effects is an interesting idea that I'd love to develop more.

So, yeah, sometimes it's important to focus on a specific botanical, and today, we'll focus on one of the key botanicals which can be utilized by aquarists to further the practice of botanical-style aquarium work- the versatile and unique Yellow Mangrove leaf (Ceriops tagal), and its use in a leaf litter bed.

Now, mangrove leaf litter- like litter from other leaves that we utilize in our blackwater aquariums- recruits fungi and bacteria which help facilitate the decomposition of botanical material, including the leaves themselves. Leaf drop in mangrove habitats- just like in their freshwater counterparts- is an important "catalyist" for biological activity, and the formation of food chains.

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 in the mangrove habitat.

Now, in the botanical-style aquarium, mangrove leaves are one of the most useful botanical materials which we can employ, for a variety of reasons. First offf, on a purely aesthetic level- they look really cool! If ever there were a leaf that has the "generic tropical" thing that we talk about so much going for it, this one would be it.

From a functional standpoint, these are surprisingly durable leaves. They seem to last a very long time before completely breaking down; often two to three months or more, in my experience. Along the way, they may recruit some biofilms. However, curiously enough, in my aquariums- both blackwater and brackish- I have seen very little in the way of biofilm "recruitment."

Mangrove leaves possess specialized cell structures, including tannin cells (hello!), and sclerieds, structures within the leaf tissue which are thought to provide mechanical "support" to the leaves and discourage herbivorous predation.

Perhaps this accounts for their durability and it certainly accounts for their ability to impart color to the water via tannins over extended periods of time? Possibly. I have noticed a nice tint to my brackish water aquariums, and it's consistent with the quantity of the mangrove leaves present.

In my experience, mangrove leaves are more than suitable for use in a freshwater (blackwater) systems. I use them in my home aquariums extensively with fantastic results.

As we've discussed many times here, Mangrove leaves also provide a unique ecological environment for diverse bacterial/microbial communities. I think the "productivity" of mangrove leaf litter beds in brackish water systems-in the wild or the aquarium- is every bit as great and important as leaf litter beds are in freshwater ecosystems.

If we examine wild ecosystems from where mangroves are found (and by extension, mangrove leaf litter beds), in addition to bacteria, they are home to a group of fungi called “manglicolous fungi.” These organisms are vitally important to nutrient cycling in these habitats...The benefits for our closed aquatic ecosystems from these organisms are obvious! This plays into one of my "pet theories" that leaf litter beds in our aquaria-fresh or brackish- serve to act as "nutrient export" systems.

If we examine this stuff further, there is also evidence (in both brackish and marine habitats) of higher fish population densities in areas which have accumulations of decomposing leaves and mangrove materials. In several geographic locales worldwide, researchers have found a highly significant relationship between amounts of mangrove detritus and fish densities or biomass in mangrove estuaries and creeks.

This is much like the "fish follow the food" idea that we've discussed many times here in the context of blackwater flooded forest habitats, such as those found in the Amazon and elsewhere. They might look slightly different in the brackish habitat, but the essential function is the same, from an ecological standpoint.

Such productive habitats are naturally of interest to us as botanical-style aquarium fans. And with the ability to at least simulate some aspects of them, the time has never been better to research mangrove habitats and the functions of the leaf litter they contain, from the comfort of our own aquariums! Since 2017, we've been pushing forward our more "functionally aesthetic" concept of a brackish water aquarium- and the basis has been...leaves.

As we gain more an more experience in utilizing mangrove leaves in our aquariums, I believe that we may see more success with brackish water AND freshwater life forms. The unique biology which these leaves support, and the compounds they release as they break down, form a basis for one of Nature's most fascinating ecological habitats.

At the risk of being redundant, let's visit that "big issue" which comes up when we talk about using these leaves in our aquariums: "Can they be used in freshwater aquariums?"

And the answer is an unequivocal, "Yes!"

These leaves are really great for blackwater aquariums, and I have used them for this purpose for years, and they've performed beautifully.

Although our leaves are collected for us on dry land as naturally fallen from a brackish water mangrove habitat, in my experience, there is no detectible salt released into the water from these leaves.

Properly preparing them (ie; boiling/soaking) should completely eliminate any lingering concerns you might have about this. I've even tested them by simply giving the leaves a quick rinse and tossing them in a small container of water, then testing the water with a digital refractometer...and voila!- no detectible salt.

So, yeah. Feel free to use 'em in your blackwater aquarium without worry, as I do.

And let me tell you, these leaves can provide a significant visual "tint" to your water! They appear to be packed with tannins which contribute a very deep, brownish-red color to the water. I've enjoyed some stunning-looking blackwater aquariums which utilized mangrove leaf litter as the basis for this type of aquarium.

When we think about using mangrove leaves in our closed-system aquariums, it's about husbandry and perspective as much as anything else...And accepting the fact that the leaves and other natural materials are part of the ecology of an aquarium, and that they will behave as all terrestrial materials do when submerged:

They'll break down and decompose, imparting their internally bound-up compounds into the water.

And of course, that leads to so much more:

They'll form the basis of a surprisingly complex food chain, which includes bacterial biofilms, fungi, and minute crustaceans. Each one of these life forms supporting, to some extent, those above...including our fishes.

When you think of these unique leaves not so much as "hardscape props", but as dynamic biological components of a closed microcosm, it all makes a bit more sense.

Stay excited. Stay curious. Stay persistent. Stay creative...

And Stay Wet.

Scott Fellman

Tannin Aquatics