The implementation of the so-called refugium among reef aquarium hobbyists in the U.S. has shone itself to be a very important development. The manner in which the refugium has developed in this country is quite interesting: It is a by-product of experimentation with two other developments — Jaubert-type plenums and Dr. Adey-type algae scrubber filtration systems. Both of these systems were initially of interest to reefkeepers as a means of exporting excessive nitrates from their reef aquariums. Speaking for myself, I wasn’t particularly interested in the nitrate removal capacity of these systems. I never found it difficult to balance the producers and consumers of organic waste in my reef aquariums, even when I only had a very thin layer of substrate for appearance only. So, nitrates were rarely a concern of mine.
However, the use of a refugium as a protected environment for a variety of beneficial organisms is a different matter entirely. To put it simply, the type of refugium I speak of is a small aquarium plumbed into the main aquarium, but protected from the main aquarium’s predators. This permits small crustaceans, for example, to reproduce and flourish. In this case, the refugium can become a source of food for the main aquarium, because zooplankton — such as the crustacean’s gametes and larval forms — growing in the refugium eventually find their way into the main aquarium. Furthermore, it is possible to grow a variety of macroalgaes — beneficial to the system as a whole — in a refugium where they are protected from herbivorous saltwater fish. In my case, I have found a refugium to be an excellent place to grow out coral fragments, nurse damaged corals, grow out small Tridacna clams, acclimate timid fish and even serve as a temporary quarantine aquarium. In the latter case, the refugium can be disconnected from the main system so that a new saltwater fish carrying a parasite cannot infect the whole system. If the refugium’s water circulation is completely dependant on the closed off plumbing, a small powerhead can supply the needed circulation until the refugium is reconnected to the main system.
For myself, plumbing in a 40-gallon refugium was quite easy. In the room behind my display aquarium I have a 300-gallon Rubbermaid fiberglass tub, which serves as a sump. It is 2 feet deep, and oval shaped at 6×5 feet. I placed the refugium in the sump. The refugium has one hole drilled through its bottom. With a bulkhead in that hole, I placed a 1-inch PVC standpipe. I bring water from the sump into the refugium with a small submersible pump. When the water level inside the refugium reaches the top of the standpipe it then drains back into the sump. The refugium sits on top of several plastic milk crates, thereby placing the refugium above the water level in the sump.
Julian Sprung located his refugium on the floor next to his display aquarium, where water is moved back and forth by small pumps. One of the reasons that Julian located his refugium on the floor was that it enabled him to grow a Florida mangrove tree, with its roots in the refugium. Locating it on the floor gives the mangrove room to grow, with artificial lighting suspended from the ceiling above it. Both Julian and I use a relatively deep sand bed, about 4 inches. Julian uses a plenum, I don’t. One of the fortunate things about my arrangement is that water from the refugium enters the sump via gravity — according to some, doing less harm to the copepods, anthropods and so on. However, planktonic life is still driven by a powerful Jacuzzi pump — 4000 gallons per hour — from the 300 gallon sump to the 400 gallon display aquarium. Whether the Jacuzzi pump’s powerful impeller damages planktonic life is a matter currently debated. What is clear is that the density of life, especially zooplanktonic life, in the refugium is much greater than in the display aquarium. I have used a flashlight, with the lights out in both aquariums, to make this comparison.
There are other uses for a refugium as well. It can serve as an aquarium to house small, delicate saltwater fish, or to test a reef-questionable fish. Before putting a butterflyfish or saltwater angelfish into the display aquarium, where it would be very difficult to remove, its eating habits can be tested in the refugium. Currently, I’m trying to get a male and two female anthiases (Mirolabrichthys dispar) to feed. They are very shy and would never learn to feed in my display aquarium.
I’m currently experimenting with trying to feed several members of the genus Dendronephthya in my refugium. I can flood the refugium, while disconnected from the main system, with various forms of plankton. After giving the experimental animals several hours to feed, I reconnect the refugium to the main aquarium. This has the advantage of placing a lot of food in a small space while avoiding having the refugium turn into a polluted mess. Interestingly, the corals in the main aquarium appear to be benefiting from this practice. I’ll have more to say about this in a future column.