OK, here we go!
As I said before, this will be an aquarium showcasing Nature, and run by Nature. The substrate will be the foundation of that. Most of all, I want it to be a good home, for both seagrasses and a wide variety of micro and macro life. Rather than a pretty, sterile decoration, I want a 'workhorse' that plays a huge role in the overall ecosystem.
I hope to grow seagrass as the major structuring element of the community. Since seagrasses are higher plants, they have roots dedicated to extracting nutrients from the substrate. In order to provide a good home for them, I need to provide a fertile substrate. So, I will incorporate dirt and mud in it, along with the sand. I've been soaking some garden soil in water for months, and I have a good source of live mud. Once the tank is up and running, fish food, fish wastes and other organic particulates will continuously settle on the substrate, where they can be processed by detrivores, etcetera, recycling them into nutrients the seagrass can use.
How will I provide a good home to detrivores? Most of the substrate will be fine and soft, so they can easily move through it and find their ideal location. Larger grain sizes will also be provided, for some refuge at the substrate surface. Most importantly, I will not be filtering out particulates or attempt to keep them in suspension. There will be no mechanical filtration. Instead, detritus will be allowed to settle on the bottom, where the detrivores can get to them, just as they would in a lagoon setting. I'm hoping to introduce a diverse 'cast of thousands' through the addition of live rock, live sand and live mud. I'll also be incorporating some specific characters that can be added separately. I was able to save a good number of spaghetti worms from the old tank. They are currently flourishing in my holding tank. I'll be adding mixed pods, serpent stars and a sea cucumber as well. All of these creatures will be a vital part of the food web.
With a heavily planted tank, bacteria's role is reduced. But I do want to provide habitat for a variety of them. Some need a lot of oxygen, some need a little, some need none. Substrate depth, as well as grain size, can provide diverse levels of oxygen to accommodate diverse species of bacteria. Larger grain sizes at the top will allow higher oxygen levels in the pore water. Medium grain sizes at the mid level will provide lower oxygen levels. Very small grain sizes and mud at the bottom will provide habitat for bacteria needing no oxygen.
So the theme of my substrate is diversity. The more diversity, the more stable the ecosystem. Fostering diversity in the confines of a box is challenging, but all the more important, given the limits of space available.
The space limitation also calls for some limits on diversity. Obviously, we wouldn't add a large predator that eats all our fish. Accordingly, I don't plan to add any creatures that would prey on the ones that help maintain the food web. For example, wrasses. These fish are smart, hunting machines. They can devastate populations of pods and other tiny creatures that are needed to keep the system functioning. So we have to prioritize our choices to optimize the overall function of the ecosystem. No one species is more important than the the whole.
I hope you find this interesting! I think substrate dynamics are woefully under appreciated in the hobby. Any questions?
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