Reefreaders

What Are They and Why in the World Would You Want One?

You’ve heard the word refugium or ‘fuge but do you really know what they are? According to Dictionary.com a refugium is “an area where special environmental circumstances have enabled a species or a community of species to survive after extinction in surrounding areas” and a refuge is “a place of shelter, protection, or safety. ”The refugiums on, or within, our aquariums perform precisely this function for our display tanks. In fact, refugiums have enhanced our ability to keep and even breed many species in our aquaria so greatly that Calfo and Fenner consider them important enough that they devote an entire chapter to the subject in their book Reef Invertebrates, An Essential Guide to Selection, Care and Compatibility.

Refugiums may be lighted or dark. A Talking Reef thread discusses a DIY dark refugium that can even be used in nano tanks. Dark refugiums, such as the one described in the thread, can function as a food farm for your aquarium by allowing tiny critters, such as copepods and amphipods, to thrive. Many fish enjoy snacking on pods and others, such as most mandarins , rarely accept any other food. Whether your fish are pod snackers or obligate pod eaters, a refugium will keep a steady supply available

A lighted refugium provides a place to grow plants such as macro-algae, seagrasses and mangroves. Macro-algae and other plants function as water scrubbers, and when pruned or harvested, provide nutrient export thus helping to maintain good water quality in your aquarium. Additionally, fewer nutrients lessen the incidence of hair algae and other nuisance algae in your display tank. The two macro-algaes that marine aquarists are most familiar with are chaetomorpha and caulerpa although there are many other varieties, some of which are quite decorative. Pods flourish in macro-algae and it also serves a nursery for baby snails.

Have you ever noticed that the pH in your aquarium is lower in the morning before the lights turn on than it is in the evening with all the lights on? You can stabilize the pH by lighting your refugium on a reverse photo period from your tank. This means that when your tank lights are on the ‘fuge lights are off and vice-versa. When the lights are on, photosynthesis is occuring and carbon dioxide, which has a direct negative effect on pH, is taken up and pH tends to rise. However, when the lights are off, "normal" respiration from all those photosynthetic organisms produces carbon dioxide which causes pH to decrease. Using a reverse lit fuge will offset this effect by contining to consume the CO2 24 hours a day, thus, stabilizing the pH of the system.

Some macro-algae, particularily the green Caulerpa species, needs proper care to avoid having it “go sexual”, which is also known as sexual reproduction or sporulation. Having your macro algae go sexual can lower oxygen levels in your tank and create a toxic environment with sometimes disastrous results. Regular pruning is absolutely necessary to avoid sexual reproduction and has to be done at least weekly with some species. Many people who keep caulerpa believe that a 24 hour photo period will help prevent it going sexual. However, with this lighting shceme, macro such as cheato would fail to thrive.

Macros, such as this species of caulerpa, require frequent pruning.

 

Adding a deep sand bed (DSB), mud substrate and/or live rock to your refugium allows for increased biological filtration in your tank. Increased filtration leads once again to higher water quality and healthier livestock. Live rock and substrates also encourage the growth of worms and other benthic¹ organisms.

Refugiums come in many shapes and sizes and may be placed above, beside, beneath or hanging on your tank. Some are in dedicated vessels, others share space. Perhaps the most common arrangement is a sump/refugium, in which a portion of your sump is set aside as a refugium. Although you may need to be creative, there is one to fit your aquarium.

 

A Hang on the back (HOB) model by CPRUSA.

 

I knew that I wanted a mandarin from the time I set my reef tank up and I realized that I would have to find room for a ‘fuge. I have a corner tank and there is limited room under the stand. A hang on back (HOB) refugium wouldn’t work because of the tank design. I use a converted wet/dry filter for my sump. For my creative ‘fuge solution, I lined the bottom of the compartment that would have held bio-balls with plastic craft canvas, added caulerpa which can’t go through the squares in the plastic canvas and then put some dry rock rubble in the area under here. I then added a 6500K compact florescent bulb with an aluminum reflector to provide a light source.

 

Photo by Carmie Jo of her Sump/Fuge modification. The inset is of the same wet/dry sump out of the box.

My refugium is not optimal. For instance, the flow rate is really too fast for proper nutrient export. Even so my nitrates dropped from 10ppm to undectable.

As a marine hobbyist you know that there are widely varying opinions on optimal reefkeeping. Some use DSB’s and others go bare bottom. Many swear by UV, ozone or both while others advise against them. However, you will find that refugiums are agreed upon by nearly everyone. So, what are you waiting for? Start your ‘fuge today!

Look for future articles on how to setup and stock a refugium.

Resources for Further Study

Dictionary.com Unabridged (v 1.1). Random House, Inc. 17 Mar. 2007. Dictionary.com

WetWebMedia Refugium Index

Calfo, Anthony and Fenner, Robert 2003. Reef Invertebrates, An Essential Guide to Selection, Care and Compatability. Reading Trees and WetWebMedia, Monroeville, PA

Tullock, John H. 2001. Natural Reef Aquariums; Simplified Approaches to Creating Living Saltwater Microcosms. Microcosm, Shelburne, VT

 

Definitions: 1 Benthic -  living on or in the sea bottom

Podcast References  Episode 54 Refugiums - Refugiums - Podcast Episode 54 Episode 88 DIY Cryptic Fuge -