Refugium Education

Reef aquaria have gotten a lot more impressive over the years. Much of this owes to a greater awareness of, and emphasis on, the base of the natural marine food chain. This necessarily has also made reef aquaria a bit more complicated. Why? For the same reason we leave out a food dish, instead of a whole, open bag of food, for our dog. Control! At the lower base of the food chain—the very bottom, actually—are the primary producers. This role is played by various autotrophic bacteria, algae and plants. At the upper base of the chain are certain (usually tiny) intermediary organisms ranging from protists to microcrustaceans (e.g. copepods). In this model, the autotrophs “make” their own food energy and biomass from inorganic sources of energy (e.g. light) and inorganic carbon (e.g. carbon dioxide) respectively; the intermediary critters feed on this food source, transferring it up the food chain as they are consumed by predators such as small fish. Small fish get eaten by larger fish, and so on… The most amazing thing about all of this, especially in aquaria, is the efficiency with which nutrients are recycled. Waste products (excess nutrients originally sequestered by the primary producers) that are generated by the “consumers” along the way are all rediverted back into autotrophic pathways. This is where the refugium comes into play. The refugium is an auxiliary tank on your main, display tank. It serves as a sort of refuge for both primary producers and primary consumers (i.e. intermediaries) such as pods. There, desirable and beneficial macroalgae are cultivated out of the reach of large, gluttonous herbivores such as tangs. Pods proliferate there too, safe from the constant predatory pressure of small fishes like damsels, gobies, etc. Even so, as the pods reproduce, they drift out of the refugium into the main tank to continuously feed fishes, corals, and so on. As the macroalgal bed grows to maximal carrying capacity, it is harvested and either discarded or (better yet!) fed out as a nutritious live veggie for fish and invert herbivores in the main tank. In this section you will learn how a refugium planted with macroalgae improves aquarium water quality and compete with bad algae, how refugia support maximal pod populations and how to smartly install/operate refugia in your own aquarium system.