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Best Plants and Algae for Refugia

Best Plants and Algae for Refugia

By: Anthony Calfo

In this column, I am excited to begin to share a series of installments with you discussing the best plants and algae for refugia. For the benefit of new readers and anyone unfamiliar with the term “refugia,” I’ll offer a brief definition. A refugium (in the most literal sense of the word) is simply a “safe place” of refuge for something from something else. In practical applications of aquaristics, however, it usually means a secondary aquarium, plumbed inline to the main display, for the protection of species that are not easily cultured or safe elsewhere in the system. The use of refugia has become very popular with aquarists of all levels and for manypurposes.

“Refugia are useful and effective compliments to marine displays. Some are designed to be an aesthetic feature, while others are hidden and perform in more practical roles like plankton reactors or “vegetable” filters for nutrient export.” photo by Anthony Calfo

The species selected for culture in refugia vary considerably. Some refugia are installed conspicuously and used as an aesthetic feature to the display. In other situations, the refugium is meant to be purely functional (utilitarian) and hidden underneath or away from the main display. An example of the former refugium would be a seagrass (Thalassia) biotope with tube-mouthed fishes (Syngnathids) in it. Neither the seagrasses nor seahorses, for example, would survive well in a typical stony coral display with very strong water flow and active, aggressive community fishes! But a seagrass refugium plumbed inline makes a handsome display in its own right, and enjoys all of the benefits of the system filtration and water quality.

Most refugia are instead meant to be practical, however, and serve a specific purpose like plankton production or nutrient export. An example of this type of refugium (utilitarian) would be a “vegetable filter” where safe, stable macroalgae is encouraged to grow and utilize nutrients from the system. The nutrients may be recycled as food when the harvested algae is fed back to the display fishes. Or, nutrients may be exported when portions of algae are systematically removed from the system. Algae-based refugia are not always attractive or tidy, but they are very effective. They also give the system other benefit too like the support of zooplankton production and pH stabilization (when run on RDP – reverse daylight photosynthesis photoperiods or with deep oolitic sand beds). While there are many other types and advantages to refugium styles, it is this latter “vegetable filter” we will focus on first here.

American aquarists are very fortunate to have a wide variety of true marine plants and algae available to us imported from abroad. Some very nice Pacific species ship well from Hawaii and the Indo-Pacific to the west coast of the US, where they are stabilized and then distributed across the country. And an even greater amount of healthy and interesting “greens” are collected for the hobby from the tropical Atlantic, Florida and the Caribbean. No doubt, the plentiful variety and availability of such species for so many years has fueled the culture and study of plants and algae that has lead to our strong interest in refugia and natural filtration methodologies. Refugia have become so popular in recent years that a growing majority of intermediate and advanced aquarists run at least one refugium on their display, and most beginners are familiar with the term if not already considering the application. It seems that refugia will be as popular and widely used as protein skimmers in the next five years; they really offer effective and exciting new filtration and display opportunities.

Some aquarists choose to use multiple refugia plumbed inline together for maximum benefits. Installations like this are often “behind the scenes” and designed for efficiency, but not necessarily aesthetic value. photo by Anthony Calfo






It is surprising that aquarists have not discovered the benefits of using refugium vessels sooner. We have such passion for keeping and studying a wide array of creatures from across many different reef niches… even from different oceans! And when we try to place these diverse organisms together, but coming from such different physical environments, it is no wonder that they do not all thrive optimally over time. Can we really expect some corals collected in less than 10 meters to live with other corals collected from below 25 meters optimally in the same aquarium? The answer of course, is no. Standardized (homogenized) lighting and water flow in an unnatural “garden reef” aquarium, as I like to call them, cannot satisfy all species from a wide range optimally. This analogy extends to many other situations that you may already be familiar with. For example, you might like to keep mandarin dragonets and you might also like active wrasses and damsels. Now even if you could get all three groups of fishes to live peacefully, they still will not all thrive together equally; the mandarin dragonet at least will be out-competed for food and suffer over time. So too is the case with keeping beautiful plants and algae… many of which will naturally sprout from live rock. The reality is that most aquarists enjoy keeping some kind of herbivorous creatures in their display tank, and often add them (too) early to the system. Thus, when surgeonfishes, angels, snails, urchins, etc. are introduced before the beautiful green, red and brown algae have had a chance to establish, the result is little or no appreciable growth of those forms. In fact, an amazing number of plants and algae are never even glimpsed because of this, yet if you have the patience to allow your live rock to develop for just four to six months without harsh herbivores in residence, you will see an amazing array of species growing from even the plainest live rock!

If you have the patience to resist adding harsh herbivorous creatures like surgeonfishes, angels and snails to your display for the first four to six months, many amazing and useful algae species can sprout from even the plainest live rock! Padina is a handsome and common algae that will grow from rock collected in the tropical Pacific.” photo by Anthony Calfo

If you really want to culture useful algae properly, thought, it is better to grow them with control in refugia and only offer harvested portions of the matter to the grazers in their remote display. This way the algae will not be subjected to the possibility of excess grazing. For some popular species of algae, like the beautiful “red grapes” Botryocladia, this is mandatory as they are too delicate to endure any amount of vigorous grazing at all. Other species are quite sturdy but simply grow too large or too vigorously, like Sargassum, for most display tanks.

One of the more popular algae species for aesthetic use in refugia is Botryocladia,”red grapes.” Although it is a crowd-pleaser for its handsome color and morphology, this algae is not ideal for “working” refugia used for utilitarian purposes like nutrient export, as it is not reliably fast growing or stable over an extended period of time for most aquarists. It is simply and aesthetic delight. photo by Anthony Calfo

Red, Green or Brown algae species can be used in “vegetable filters” with varying success. Before you ponder what species to keep, you must first consider your principal goals for using them. There are shared benefits between most all of them, but some significant disadvantages too. Some grow faster than others and make better nutrient export vehicles. Some are more noxious (toxic to fishes, corals or other algae) and can be a risk if left unchecked or when pruning (systematic harvest) is neglected. Others are more stable and less noxious, but perhaps slower growing. Certain types instead afford better incidental co-culture of microcrustaceans (copepods, amphipods and mysids), which serve as coral and fish food (zooplankton). And there are species which are barely edible at all by herbivorous fishes, yet they make great refugium species for other reasons.

What is your interest in keeping a “vegetable filter?” Please join us in future installments as we profile the advantages and disadvantages (“pros and cons”) of specific plants and algae for refugia.

With kind regards,
Anthony Calfo