Intro to Refugium Algae

Introduction:

The California coast is home to prolific kelp forests. They are magical places that are teeming with life, not unlike a coral reef aquarium. The tall columns of Macrocystis species kelp reach from the bottom to the surface, and at the right time of year, cover the surface in a golden canopy. They cleanse and oxygenate the water, and create large three-dimensional habitats for numerous important species. Similarly, an aquarium refugium housing macroalgae cleans, oxygenates, and provides habitat for important invertebrates. The connection is obviousin both systems, macroalgae regulate chemistry and protect animals important to the environment.

Macroalgal refugia have become a popular addition to reef tanks, and with good reason. They provide numerous benefits when managed properly. On the other hand, a poorly maintained refugium can cause serious system-wide problems. There are also misconceptions about the right way to keep macroalgae. It seems prudent, then, to address the topic of macroalgae as it pertains to aquarium refugia.

What is algae?

There is an entire branch of science, called phycology, dedicated to the study of algae; algae are difficult classify. They are not animals nor are they plants, so they do not clearly belong to any one category. However, algae are undeniably similar to plants, since they have photosynthetic pigments.

Describing algae is no easier than defining what they are, since the variety of habitats, body forms, and photosynthetic pigments they use is vast. Algae are primarily aquatic photosythesizers. Even the most complex algae are far less so than plants, lacking specialized tissues. They do not possess roots, flowers, leaves, or stems, and their cells are fairly simple. Some are unicellular, like the brown diatoms we aquarists despise. These algal cells may actually be very animal-like, and can be difficult to distinguish the simplest types of animals. Others algae are multicellular, such as the coralline algae we aquarists covet. Multicellular algae, or seaweeds, are recognizable because they are generally big enough to see. They have leathery blades that resemble leaves and are covered in slimy substances called carageenan. A typical refugium may contain either or both of these two groups of algae. When differentiating algal groups, the details of their reproductive cycles are defining characteristics. Some algae have two distinct phases of life, delineated by the number of chromosomes present in the individual at a given time.

The Fuge:

In aquarium terms, a refugium is a separate reservoir where macroalgae and small invertebrates are cultured. The fuge is used to protect the main display from algae the aquarist wishes to remain unseen as well as protecting algae and inverts from fish that would otherwise consume them too quickly. The refugium also protects the whole system from nutrient build-up and daily pH swings.

Strictly speaking, a fuge is a box of macroalgae, and perhaps a deep sand bed and some live rock. For practical purposes, it is popular to combine the fuge with other components of a sump to make a sump/fuge complex. However, without some aggressively small micron filtration upstream of the fuge, this practice often ends up making the fuge a trap for detritus. Alternatively, hang-on-back (HOB) boxes are attached to the sump tank, or the back of the main tank. Regardless of the particulars, the goal of the fuge is the same: provide a safe place for macroalgae to scrub the water of micronutrients. Actually, combining a deep sand bed sump with a refugium can be a workable scenario, not only because it saves space, but because many macroalgal species prefer to anchor in sand or on live rock. Other varieties, like Chaetomorpha, are perfectly fine when floating freely at the surface.

What does the Algae do?

The fuge algae accomplish four main things, all of which are important. First, the macro takes up dissolved nutrients, especially nitrates and phosphates. The macro is typically adept at out-competing nuisance algae for these chemicals, so tanks with healthy refugia are less likely to have an unsightly outbreak. The second benefit of macro is that it can be put on the opposite light cycle as the main display. Doing so allows 24-hour photosynthesis to occur, which helps to keep pH / oxygenation levels stable. This is important since cellular respiration, which occurs continuously and acts to lower pH, counteracts the tendency of photosynthesis to raise pH. By having photosynthesis occur 24 hours a day, aquarists can achieve near pH equilibrium in a natural way. In a sense, the third benefit of macro is a side effect of number 2. The fuge algae releases oxygen into the water as a side effect of photosynthesis, the results of which are increased dissolved oxygen (DO) content and oxidation-reduction potential (ORP). Lastly, macro provides habitat and spawning areas for micro-invertebrates like copepods, amphipods, and decapods. Both the adult animals and their eggs get circulated throughout the aquarium when the sump is fully colonized, feeding fish and filter-feeders alike adding a significant stream of nutritious live food to the aquarium system.

A Few Macroalgal Candidates:

Caulerpa sp.Invasive algae, illegal in many areas; not a great candidate due to die off events that can lead to massive pollution levels.

Halymenia sp.Dragons Breath algae; good candidate, strong nutrient exporter; grows exceptionally fast; beautiful fluorescent red color also makes it sightly for main displays.

Chaetomorpha sp.Excellent fuge algae; grows quickly and exports nutrients well; floats at surface so it is easily harvested; loose pieces may end up floating around main display.

Penicillus sp.Shaving Brush Plant; less commonly available; nutrient uptake is moderate once established and it will consume calcium and iron from the water column.

Halimeda sp.Cool looking algae, has unique segmented structure; hard calcium skeleton, that is less likely to be eaten by herbivores, but production of which costs dissolved calcium; can reproduce quickly and is invasive in many areas such as Hawaii.

Lighting conditions:

The real key to maximizing the productivity of a refugium is to give it light in the right way. To do so, there are two basic factors to consider: light color and photic cycling. Light color is pretty easy. Most macroalgae you are likely to encounter are shallow water speciesin some cases very shallow. They do best with 6500K light which is more like gardening lighting than most stuff you see for the aquarium trade. As for the photic cycle, there are two basic options since you shouldn't run the fuge lights on the same schedule as those on the display tank. A) Run the fuge lights on a schedule opposite to those on the display tank; B) Run the fuge lights 24 hours per day.

You shouldn't run the fuge lights on the same schedule as the tank because the pH will fluctuate more from day to night. A) Running a so-called reverse daylight cycle allows photosynthesis occurs more evenly throughout the 24-hour period, allowing O2 and CO2 to develop a balance. The balance means stable pH throughout the cycle. Essentially, when the display lights are on, the fuge lights are off, and vice versa. The key is to create a situation of perpetual, consistent photosynthesis that does not fluctuate throughout the day or night.

C) The 24-hour fuge light cycle is popular because it is thought to prevent Caulerpa from going sexual, as well as providing maximum nutrient uptake. Caulerpa can go sexual when not provided enough light, which often happens at the bottom of a thick algal canopy in a refugium. When it does so, A large portion of it can dies off releasing pollutants back into the tank water (clearly not ideal). These problems are avoidable. There are algal species available that can do the same job without this risk. Also, fuge algae should be harvested regularly to remove the exported nutrients so that there is no chance that they can be re-released into the water. In this lighting model pH swings will still be reduced but perhaps less so than an opposite lighting schedule, it all depends on the size of the fuge, and how much is growing in it. You should do some tinkering with your system to find out what lighting schedule is best for you.

Works Cited:

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