As you know, we're big lovers of all sorts of "niche" biotope-type aquariums.
One of our long-time favorite niche habitats that's just begging to be replicated is the brackish-water Mangrove thickets of...well, pretty much any tropical region. These are amazingly rich, biologically diverse and productive habitats, combining many of the attributes of coral reefs and freshwater riverine systems. And although hobbyists have played with them before in aquariums, there has been less emphasis about recreating the ecological composition and characteristics of the habitat than there has been about simply keeping the Mangroves and some fishes. Now, despite some of the inevitable naysayers, who will tell us that "you can't do that" (just like the resistance we once encountered with leaf litter/botanical blackwater tanks...), I am confident that just trying to work with this concept will yield interesting discoveries. That whole "doing versus talking negative about" thing comes into play once again...
Mangrove thickets and their associated ecological communities are pretty incredible!
The basis for these thickets are, of course, the Mangrove trees themselves. Rhizophora mangle, commonly known as the "Red Mangrove", is one of the most common species associated with this habitat, and is a remarkably adaptable plant, forming the "anchor" for a web of life in this fascinating environmental niche. This plant is a "facultative halophyte", which is a fancy way of saying that it's able to thrive in fresh, brackish or total saltwater. It shows a tremendous resiliency and hardiness. The Red Mangrove has a unique ability to filter out the salt and only draw freshwater.
Red mangroves dominante the shorelines of estuaries and marshes, from the upper subtidal to the lower intertidal zones, and are distinguished from other mangroves by networks of prop roots that originate in the trunk of the tree and grow downward towards the substrate. Red mangroves may attain heights of up to 75ft (25 m)! Soils in mangrove areas tend to be fairly anoxic ( depleted of dissolved oxygen), preventing many types of plants from taking root. Mangroves have adapted to this condition by evolving very shallow root systems, rather than deep taproots into the substrate. Red Mangroves aerate their roots by way of "drop roots" and "prop roots", which develop from lower stems and branches, and penetrate into the surrounding substrate only a few inches. The "prop roots" serve to stabilize the tree, and to provide critical aeration to the roots in the demanding environment.
And here's where this environment really gets interesting for us "botanical-aquarium types":
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! Now, they're different types of leaves than we are currently using in our blackwater tanks, but the concept is entirely familiar to us.
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. We collectively 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? I think so. Now, first off- I have no illusions about using live Mangrove plants (available as "propugles") to serve as "nutrient export" mechanisms as they do in nature. 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.
However, we could at least grow a few, for the enjoyment of it all, and utilize faster-growing, adaptable aquatic plants to provide some natural nutrient export. And of course, we could skip the live Mangroves altogether, and just utilize some driftwood (as has been done for decades) pieces to simulate the roots...However, the similarity to the aesthetically-driven "Mangrove thicket" tanks of the past ends there! We'd continue on, concentrating on building up the other "functional" aspects of the Mangrove habitat!
(Not just a bunch of typical fish geeks..Myself, Charles Delbeek, Tony Vargas, and Julian Sprung, checking out Julian's Mangrove refugium at his office at Two Little Fishes. The closest thing I've seen in a private aquarium to what we're talking about here...)
Utilizing very rich aquatic soils, similar to what has been used in "dirted" tanks by aquatic plant geeks, yet with a buffering component (finer, aragonite or calcareous substrates), we could create a "workable" plant environment, couldn't we? And by managing the water quality with regular, frequent water changes, and careful, automated topoff to keep specific gravity constant at a low brackish level (like-this is a fundamental thing), wouldn't we be able to simulate this environment on at least a superficially functional level? Kind of like what we're doing with blackwater, leaf-litter-bed aquariums?
Now, we have to learn a bit more about the impact of high-nutrient substrates, decomposing leaf litter and such in brackish systems, but it's a totally cool experiment, IMHO!
Mangrove habitats also function as fish "nurseries" and feeding zones, assist in preventing shoreline erosion because of their ability to trap sediments in the low-energy waters of brackish estuaries and breaks up wave action within their maze of prop roots. These prop root systems are just screaming at us as fish geeks to play with. I've waded, snorkeled and scuba dived in Mangrove systems many times, and am always blown away by the myriad of tempting aquarium possibilities that they inspire!
Numerous "sublittoral/littoral" organisms utilize the prop root zone of red mangroves as their primary habitat. The "prop root zone" provides sessile filter feeding organisms, like such barnacles, muscles, tunicates, and bryozoans with a perfect environment in which to live and reproduce. There are sponges in brackish ecosystems, but they are highly specialized feeders, often deriving sustenance from a very specific type of dissolved organic food source, so we're unlikely to be working with them. Oh, you also have the "seldom-kept-in-aquaria-intentionally" polychaete worms and "boring" crustaceans, like isopods.
Some of these animals may be kept in aquariums...yeah, you're probably thinking what I'm thinking, right? The wheels must be turning by now! And of course, other, more "aquaristically familiar" animals, like shrimp, crabs, snails, and...fishes! All of these creatures utilize the "prop root zone" of mangroves as a feeding area, refuge and spawning area.
So, you could create a very interesting little biotope aquarium by replicating many aspects of a Mangrove thicket! Now, aquarist have "messed around with Mangroves" for decades. Growing small ones in reef and even brackish tanks is not new. And this little blog is NOT about "How to use Mangroves in the aquarium." However, when you refine and focus on the idea of replicating the community and complexity of life which inhabits these zones, you're entering "the bleeding edge" of aquarium keeping. By bringing in some of your varied aquarium-related talents, from planted aquariums, reef tanks, blackwater/botanical-style fish tanks, and even riparium and vivarium experience, an entirely new type of aquarium system is possible!
(Yes, I am a fish geek. This stuff gets me pretty excited! Always has.)
By examining at these habitats and the aggregations of life forms which inhabit them, and attempting to recreate some of the "functional" aspects of them (not just throwing in some wood to simulate Mangrove roots, adding some salt and a few Archerfish and calling it a day...), like epiphytic life, "living" substrates, etc., we can begin to investigate, learn about, and experiment with what would best be labeled a "brackish-water botanical-style" microcosm!
This is exactly why we are launching "estuary." It's part of our ongoing mission to offer a unique selection of products, ideas, and inspiration, to help you merge a variety of aquatic skills and experience together to create some incredibly unique systems!
Interest piqued yet? Maybe a little?
Stay tuned for more in the near future. We're just getting started here. Who's in?
Stay excited. Stay bold. Stay creative.
And Stay Wet!