What is a Refugium?

As the marine hobby progresses, aquarists all over the world continually strive to provide the most natural and healthy environment possible for their pets.  Because of the constant tinkering and sometimes questionable experimenting, new approaches are discovered that help move the hobby forward.  This could be said for the recent popularity explosion of the refugium.  Although the attributes provided for by a well established and maintained refugium is not new to the hobby, the understanding and acceptance of them by more and more people everyday is!  Basically, a refugium is an environment that provides protection to a multitude of creatures that are not only useful to the system as a whole, but if established and run properly can lessen the maintenance and increase the stability associated with aquarium keeping.

Substrate

The first and one of the most integral factors for the refugium is what kind of substrate to establish. Depth should be no less than 3 deep and no more than 5 deep.  The size of the sand grains used should also be paid particular attention to.  It should not be composed of all fine sand, nor should it be composed of all crushed coral.  The granular size as well as the depth of the sand bed will be the two governing factors for not only the rate of oxygen penetration, but also the types of oxygen poor microenvironments.  If the sand bed is too shallow, then the proper oxygen deprived environment will not be created.  Likewise, if the sand bed is to deep, then improper oxygen-deprived environments are created.  The grain size also contributes to the degree to which oxygen will penetrate.  If the sand grains are too small, then the sand bed will be too compact to allow the proper rate and depth of oxygen penetration.  If the sand bed is too coarse, then the it will not be compact enough and oxygen deprived environments will not be created.

Lighting

Often corners are cut when supplying light for a refugium.  Although a refugium is usually an add-on dynamic and thus considered an accessory, it is the quality of the design than propels it to integral to a well functioning low maintenance system.  No expense should be spared on the lighting.  Most of the algae that are utilized in a refugium come from relatively shallow water.  Because of this they are adapted to receiving the same quantity and quality of light as most of the corals.  The intensity of the light for the refugium will be the primary factor as to the rate of photosynthesis.  The rate of photosynthesis will be the governing factor as to the consumption of nutrients.  And, the consumption of nutrients produced by feeding the animals in the aquarium is half the reason for having a refugium in the first place.

Photo-Period

The photoperiod is the duration of light on the refugium.  The various macro-algae used in refugiums are also adapted to receiving the same photoperiod as corals.  This is usually 12 hours of light to 12 hours of dark.  By having the aquarium and refugium photoperiods opposite of each other, a greater stability in the systems pH can be achieved.  Usually aquariums will accumulate more CO2 during the dark period as there is less consumption of it in the aquarium when the lights are off.  When the CO2 goes up, the aquariums pH goes down.  So, if the refugium lights are on when the aquarium lights are off, the CO2 from respiration will not accumulate as the algae in the refugium is using it for growth.  Thus, the pH does not shift as much.  As a side note, a recent trend has been to leave the refugium lights on 24 hours.  This is unnatural and will lead to a less productive refugium.

Algae

The type of algae used and the care given to it can have a profound effect on the stability and productivity of a refugium.  Most refugiums are inhabited by species of Calerpa.  They are fleshy and fast growing.  Because of this, they have the capacity to take up a lot of nutrients.  However, pruning Calerpa every 2 to 4 weeks is necessary and will keep it in a very productive state.  Pruning  Caulerpa will also prevent it from reaching a reproductive state.  If the Caulerpa does reach reproduction, then it will turn white as it expels all of the nutrients it has locked up in growth. In other words, pollute the tank.  Just keep it pruned!   Other excellent algae used in refugiums  are Valonia sp. and Chaetomorpha sp.  The latter two  require much less care and maintenance than Caulerpa sp.  There are also red and brown algae that can be used with success.  They are usually less common and command higher prices.  They also dont tend to be as productive as the green algae.

Inhabitants

With time and care animals of all sorts will populate and reproduce in a refugium.  It will include, but certainly not be restricted to, amphipods, isopods, decapods, mysid shrimp, and a plethora of worms and bacteria.  These are the critters that are the other half of the reason to invest in a quality refugium.  Not only do they become an integral part to the processing of the organic matter generated in the aquarium, but they will live out their short yet natural life in the refugium.  In the process of doing this, a natural and continual food source will be provided by the larval production of these critters.  Adding animals that sift the sand or that have to specifically be fed will alter the balance that could be created.   Although it might be difficult, the temptation to use the refugium as another aquarium and to stock it with livestock should be resisted.  However, if the refugium is 10 gallons or larger, a few shrimp could be appropriate.  Two to three peppermint shrimp or a mated pair of coral banded shrimp could be added without to much impact.  These shrimp do not need to be fed large amounts of food and can even reproduce and create another size of zooplankton for the aquarium.  What you want to avoid are fish, sand sifting starfish, large predatory crabs, etc.  You want to avoid animals that will target the organisms that you set up the refugium for in the first place.

Conclusion

These are just some of the major aspects to a refugium.  Many other details can be discussed and explained in an more informative format by consulting with an AquaTouch employee.  Designs to incorporate a refugium into an existing system, as well as an inclusion in a system still in the planning stages can also be discussed with an AquaTouch employee.  So if youre ready to increase the dynamics, diversity and stability of your aquarium system, as well as decrease the maintenance associated with it, then consider adding a refugium to your system.  Your fish and corals will love you for it!

Prepared by Scott Davidson