Actualy, the same area of our tanks on a wild reef holds a HUGE amount of life, more than we will ever see in our tanks, and with greater numbers and diversity of life forms. The reason we will never see those numbers and diversity in our tanks is simply due to their being enclosed systems. Within that diversity there are of course predators and on a small section of a reef, they find, catch and eat their prey, which are then restocked by the prey species migrating back into that predators small territory. Given all the sessile and mobile predators, be it corals, filter feeders, shrimp, crabs and on and on that are found in such small areas, The vast majority of life on the reef reproduce by broadcasting their spawn out and up into the currents to get them away from the reef to where they can grow up in the relative safety of open ocean and then return to the reef when they are large enough to have a chance. Were it not so, a few predators in a few square feet would easily wipe out their prey species, just as happens in our tanks. So do we just give up ?
No way! It is still very possible to have a functional reef ecosystem if we understand a few things and accept the fact that our tank's diversity is going to have limitations. The beauty (and fun) of it all, is being able to play God if you will, and by that I mean we get to decide who gets in the pool or not.
Since this is a post and not an article, I will try to throw the basics out there per a reef set up.
Sump with ATS or a dedicated ATS = Control of nitrates and phosphates while providing a habitat that generates a great deal of life that becomes not only live food for the main tank, but also use and recycle many nutrients on their own, an unseen, microscopic clean up crew, that... feeds your corals and other inverts. Below are just a few examples of the life that lives in such algal mats. All taken from my algae scrubber.
See
THIS ARTICLE for complete details
Also note that 80% of zooplanton in the wild is comprised of copepds, so if you have good "pod" numbers, you are 80% of the way there already.
Seagrass Refugium and/or a
MacroAlgae Refugium (links are detailed articles) - Yet more habitats that contain ungodly amounts of life forms while....clearing the water of even more nutrients, that and such a planted tank simply looks great all unto itself. Due to space limitations I opted for the macroalgae refugium which at lights off proves to me every night just how much "food" is being made available to my corals and other "pets".
The main display tank - Now that the water is cleaned of dissolved nutrients at NSW levels and is full of live food swimming around, a live DSB (deep sandbed) is yet another wonderfull habitat, not only in providing even more food but the nutrient dynamics that take place in and on the sand is another benefit.
Live Rock & Sand
So getting back to the problem of enclosed spaces. This is where having a quarantine tank to keep and inspect live rock comes in handy, allowing you to identify and remove potential problem species, which are usualy obvious as crabs and such. Stocking all of the tanks is critical per species selection. In the coral display tank, you want a good assortment of herbivores that include both snail and fish species, which on a wild reef is critical because without that variety, the coral reefs would quickly become algae reefs regardless of nutrients or not.
A Reef Aquarium Clean up Crew. Per fish species, I hate to say it, but for this type of ecosystem, only herbivore and planktivore species should be allowed. A single wrasse for example can and will devastate your live food production as well as consume a lot of the sessile life that makes live rock that much more alive and interesting. You of course do not want many herbivores (if any) in the algaes tanks for obvious reasons. Such refugiums do however make great places to keep a something like a cuttlefish which is not going to consume your zooplankton. Also, since all food chains/loops depend upon algae, most notably phytoplankton, drip dosing your tank throughout the day and night will feed all of that zooplankton and spur them to reproduce even more. Thus enabling you to cut back on dead food inputs into the system.
So... given the above, all you actualy need are the tanks, a way to stimulate photosynthesis (lights) and a means to move water around (pumps and overflows). Supplement calcium, carbonates and magnesium and you have yourself a reef ecosystem without having to fund the hobby industry that has been trying to get us to keep single tanks alive for 50 years now and are still failing at it, at our exspense and the lives of our pets, all the while we are stuck looking at some corals sitting on top of some rocks and telling our friends " Look at my reef tank"....lol, when it can all be so very much more. IF we take the time to do it right.
Oh, and a skimmer is optional, I have one rigged up and ready to run but never use it unless there is a water emergency such as when all the snails decide to breed and make a milky mess out of everything. Other than that, it sits there collecting dust. I also only do water changes maybe once every 3 to 4 months now at about 15 percent and only do so probably just out of habit or unwarranted fears as I know it could all probably go much longer if I ever got the nerve up to do so.
Chuck