January 08, 2021

The legacy of leaves.

Among botanical-style aquarium enthusiasts, the idea of adding leaves to our aquariums is just "what you do." The idea has come out of the shadows as some sort of weird and risky thing, and become more of a "standard", complete with considerations, techniques, and "best practices."

Probably the biggest consideration when you work with leaves is to utilize those which have naturally fallen and dried up.

Dead, dried leaves such as those we favor don’t have nearly the impact on water quality, in terms of nitrate, as fresh leaves would, when added carefully and slowly. I’ve routinely seen undetectable nitrate and phosphate levels in well-managed aquariums loaded with leaves. This is largely because dead, dried leaves have depleted the vast majority of stored sugars and other compounds which lead to the production of nitrogenous substances in the confines of the aquarium.

To understand this more fully, let’s look at what happens when a leaf dies and falls into the water in the first place.

At some point, the leaves of deciduous trees (trees which shed leaves annually) stop photosynthesizing in their structures, and other metabolic processes within the leaves themselves begin to shut down, which triggers a process in which the leaves essentially “pass off” valuable nitrogen and other compounds to storage tissues throughout the tree for utilization. Ultimately, the dying leaves “seal” themselves off from the tree with a layer of spongy tissue at the base of the stalk, and the dry skeleton falls off the tree.

The fact that they have depleted the majority of their "onboard" sugars and other compounds is something that we as hobbyists should take away directly when we consider adding them to our aquariums.

As we know by now, in Nature, when these leaves fall into the water, or are immersed following the seasonal rains, they form a valuable substrate for fungi to break down the remaining intact leaf structures. And the fungi population helps contribute to the bacterial population, which creates the now-famous biofilms, which consist of sugars, vitamins, and various proteins which many fishes in both their juvenile and adult phases utilize for supplemental nutrition.

And of course, as the fishes eliminate their waste in metabolic products, this feeds these lower life forms, and contributes further to the aquatic food chain. And yeah, it all starts with a dried-up leaf!

A pretty amazing "legacy" for a humble leaf, wouldn't you say?

Hence, leaving leaves in to fully decay in your aquarium likely reaches a point when the detritus that is produced is essentially inert, consisting of the skeletonized sections of leaf tissue which can decay no further. Dead leaves contain largely inert forms of polysaccharides, and are rich in structures like lignin and cellulose, all of which are utilized by various microorganisms and fungi within the "food chain."

Utilizing leaf litter in our aquariums opens up all sorts of possibilities for interesting experiments.

And of course you can grab leaves! Why this is even debated on forums and such is beyond me. Like, the ONLY leaves you can use in your aquarium must be purchased from us or some other online vendor.

That's just fucking stupid.

Which leaves can you collect yourself and use?

Magnolia is an obvious one for many people in North America. There are plenty of references for identifying the specific species you have in your area. We've personally tried a few varieties, and have determined that no one variety is substantially better than another.

The important thing is that you collect them as naturally fallen, not "green", and that you rinse them and take the time to wipe them off and dry them a bit more before use. While you can use Magnolia when they're nice and crispy, I personally prefer them when they're recently fallen and not quite dried up.

In this particular state, they're not only more attractive, I think they tend to last a bit longer and prepare better...and they recruit biofilms nicely. Anecdotally, then tend to impart more color into the water when they're in this more "freshly fallen" state.

Their waxy "dermal" layer retains moisture, and they can get moldy if packed away too soon after they've fallen. The mold is not necessarily harmful, and can typically be wiped away and eliminated via boiling during the prep process, but it is unpleasant!

Oak, Beech, Ash, and many other leaves are commonly used by aquarists.

At the risk of over-generalizing, numerous species of naturally fallen, dried leaves are perfectly safe for use in aquariums. Personally, other than some obviously-known toxic species, or species which are known to contain oils and other dangerous compounds, I'd try just about any leaf. Again, I said "personally"- because no one can guarantee the suitability of "any old leaf"- this is just my "comfort zone."

There are literally hundreds of possibilities here- but I can't give you the pros and cons on each one. Some may have toxins or oils in their tissues which can be problematic, even deadly. The reality is that you'll need to research, collect, prepare, and experiment with them on your fishes carefully. When I receive those DM's and emails asking me, "Are ________ leaves are okay to use?" -this is the exact answer I give.

Don't like the idea of experimenting with your fishes like that? Well, we know this place online where you can get leaves that are "fish safe!" 😆 (Oh, shit- Included a blatant commercial pitch...Now you can't trust ANY of the information in this blog! Right? Sorry. 😞)

So, the next obvious question, besides which leaves to use, would be to ask, "Why would you want to do this?"

Well, it starts by looking at our biggest source of inspiration: Nature.

In Nature, as we've discussed many times-leaf litter zones comprise one of the richest and most diverse biotopes in the tropical aquatic ecosystem, yet until recently, they have seldom been replicated in the aquarium. I think this has been due, in large part- to the lack of continuous availability of products for the hobbyist to work with, and a lack of real understanding about what this biotope is all about- not to mention, the understanding of the practicality of creating one in the aquarium.

Long-held fears and concerns, such as overwhelming our systems with biological materials, and the overall "look" of decomposing leaves and botanicals in our tanks, have understandably led to this idea being relegated to "sideshow status" for many years. It's only been recently that we've started looking at them more objectively as ecological niches worth replicating in aquariums.

And man, they are!

In the tropical species of trees, the phenomenon of "leaf drop" is hugely important to the surrounding forest environment. Vital nutrients are typically bound up in the leaves, so a regular release of leaves by the trees helps replenish the minerals and nutrients in the soils which are typically depleted from eons of leaching into the surrounding forests.

Quite literally, leaf litter beds occur when leaves from surrounding forest trees fall into streams and rivers below, or submerged following seasonal inundation of the forest floors. These accumulations of leaves become. literal "oases of life." Organisms of all types are "recruited" by these aggregations, and fishes are drawn to leaf litter beds to shelter, feed, snd spawn.

Over time, many of these leaf litter beds continue to accumulate more leaves, and grow in size, essentially becoming semi-permanent topographical features in the regions in which they accumulate, often lasting for many years.

They're compelling.

In my research, I stumbled upon an interesting except from an academic paper on Amazonian Blackwater leaf-litter communities by biologist Peter Alan Henderson, one that is useful for those of us attempting to replicate these communities in our aquaria:

"..life within the litter is not a crowded, chaotic scramble for space and food. Each species occupies a sub-region defined by physical variables such as flow and oxygen content, water depth, litter depth and particle size…

...this subtle subdivision of space is the key to understanding the maintenance of diversity. While subdivision of time is also evident with, for example, gymnotids hunting by night and cichlids hunting by day, this is only possible when each species has its space within which to hide.”

In other words, there is an orderly world contained within leaf litter beds, almost like coral reefs. Different species fishes inhabit different sections of the leaf litter bed, and we should consider this when creating and stocking our biotope systems...

The implication for aquariums is that we could literally create a diverse fish community by embracing a deep leaf litter bed as the "theme" of the aquarium. This is really neat stuff, and we're just scratching the surface here!

So, beyond just creating an aggregation of material which imparts tannins and humic substances into the water in our tanks, and adds some color to the water, we're creating a little habitat, every bit as interesting, diverse, and complex as any other we attempt to replicate. In the aquarium, you need to consider both practicality AND aesthetics when replicating this ecological niche.

Suffice it to say, the leaf litter bed is a surprisingly dynamic, and one might even say "rich" little benthic biotope, contained within the otherwise "impoverished" waters. And, as we've discussed before on these pages, it should come as no surprise that a large and surprisingly diverse assemblage of fishes make their homes within and closely adjacent to, these litter beds. These are little "food oasis" in areas otherwise relatively devoid of food.

Nature and aquarium both benefit from these aggregations of leaves aquatic habitats.

As we’ve discussed repeatedly over the past couple of years, there are so many benefits to painting leaf litter in the aquarium in some capacity. Wether it’s for water conditioning, producing supplemental food, providing a home for speciality fishes, or simply to create a cool-looking display, the possibilities are endless.

The many benefits of leaf litter in both the natural environment and in our aquariums make them invaluable educational tools, helping us learn more about the form and function of the wonders of Nature.

Could all of this playing around with leaves be more of a "technique" than the aquarium hobby has previously considered?

I'm thinking so!

This spirit of experimentation, evolving technique, and understanding is just a part of the wonderful legacy of leaves.

Stay creative. Stay thoughtful. Stay bold. Stay diligent. Stay experimental. Stay curious...

And Stay Wet.

Scott Fellman

Tannin Aquatics