I was introduced to the verdant world of aquarium mosses as a teenager. Shortly after purchasing some guppies, I noticed a tiny sprig of green on the bottom of the quarantine aquarium, perhaps a centimeter long; no doubt this serendipitous speck of greenery had been included unnoticed in the bag my fish came in. Over the ensuing weeks and months, I watched with growing fascination as the tiny fronds of moss spread.
Soon, I began to take clumps of the accidental treasure and “seed” my other aquariums with it. Before long, I had plenty to spare, and I was using it as a spawning medium for zebra danios (Danio rerio) and white clouds (Tanichthys albonubes). I enjoyed that moss for years, and my experience with it led me to become a bit of a bryophile: a moss-lover.
I am not alone; many aquarists are attracted to aquatic mosses. Perhaps it is the way that they naturally tend to creep slowly across rocks and driftwood, softening their harsh edges and imparting a natural feel to the aquascape. It could be the bewildering array of shapes, growth habits, and subtleties of hue that they feature.
Some aquarists even use them to create green carpets or lawns in their aquariums. Then there are many practical benefits that mosses provide in an aquatic ecosystem. Whatever the reason, aquatic mosses have been a fixture in the hobby for years, and in recent years, mosses have had a surge in popularity. Accompanying (or more likely causing) this increase in popularity is a similar boom in the availability of aquatic moss species, each with a different flair.
Unlike some exotic aquarium plants, many of these mosses are relatively undemanding, almost as forgiving as the nearly immortal Java moss. Very few mosses require supplemental CO2, and most do well in low to medium light. The pH values in a given aquarium, if appropriate for fish, generally suit mosses. Since mosses do not have true roots, special nutrient-rich planting substrates are unnecessary, and aquarium size is not critical. Fortunately, mosses are simplicity itself to propagate. They have a lot to offer to freshwater aquarists of any experience level.
Benefits of Moss
The aesthetic benefits that bryophytes (mosses) impart to an aquarium have already been mentioned, but there are several other distinct advantages to including aquatic mosses. First, bryophytes can contribute to improved water quality. Like other plants, they absorb various nutrients, including nitrates, from the water column. Unlike many other more demanding plants, they can do this efficiently without high light levels or an intense fertilizer regimen.
Some hobbyists are inclined to think that because plants reduce nitrate levels in an aquarium, water changes are somehow less necessary. This is not the case; instead, think of the moss as making the water in the aquarium more habitable between changes. Of course, as they photosynthesize, mosses also produce life-giving oxygen and release it into your aquarium water.
Breeders of many species of fish like to keep a good supply of moss on hand. Soft mosses make a great spawning medium. Many egg-scattering fish will spawn readily in Java moss, and just-born livebearers will hide in it. In fact, a healthy crop of moss provides an ideal place to hide and rest for any of the more shy, smaller inhabitants, whether they be tiny adults, young fry or shrimp. As an added bonus, many forms of microscopic and near-microscopic life abound in the fronds of Java moss, so when young fish or shrimp get hungry, they pick a meal from the moss while remaining safely hidden from predators. There is little wonder why many fish breeders keep ample quantities of Java moss on hand.
Anatomy and Taxonomy
Although the terms are often used interchangeably by the uninitiated, mosses and algae are not the same thing. Algae are (largely) aquatic; mosses are thought to be the earliest plants to leave the seas and conquer the land. The primitive origins of bryophytes are reflected in the fact that they lack the flowers, seeds, or true roots of the “higher” plants. Perhaps most significantly, they lack the vascular systems that allow other types of plants to carry water and nutrients to great heights. That is the reason that you never find mosses — on land, at least — that exceed more than a few inches in height. Because mosses occupy their own branch on the family tree of the plant kingdom, a few key terms exist when describing their anatomy. Rather than “roots,” “rhizoids” is the term to use for the tiny structures that allow mosses to attach to surfaces such as rocks. Instead of “branches,” the term “fronds” is often used. There is some argument over whether the leaflike structures are properly called leaves, leaflets, or something else altogether. The reproductive bodies that mosses produce, to be carried by wind or water to germinate in a suitable spot, are called “spores”; the structures that produce the spores are called “sporophytes.”
Not Just Any Moss Will Do
I have read accounts of aquarists who, during a hike in the woods, become enamored with the beauty of a clump of moss growing on a rock or a tree. They then tear it from its moorings, take it home and plunk it into their aquarium. There are at least two reasons to avoid doing this. First, there may be legal restrictions against collecting mosses in the wild. Second, terrestrial mosses may or may not thrive in an aquarium — most will not. Mosses that are generally kept in aquariums are either true aquatic mosses or adaptable semiaquatic mosses that happen to fare well when kept continually underwater.
Fortunately, there are plenty of aquarium-approved mosses to satisfy the most ardent bryophile. Even these species, though, have several requirements to be met in order to keep them healthy.
Temperature. One of the most important requirements is that mosses prefer relatively cool temperatures. To illustrate the effect that a few degrees of difference in temperature can have on moss, consider the following. When I lived in Hawaii without air conditioning, the temperature in the house was in the low- to mid-80s Fahrenheit during much of the year. Under these conditions, the Christmas moss in these aquariums lived, but it grew very slowly, and its fronds did not exhibit the characteristic Christmas tree shape that this moss is known for. However, the Christmas moss I kept in my air-conditioned office, maintained in the low-70s, grew luxuriantly.
So if you want your mosses to grow quickly and look their best, keep them cool. I get the best results in the low- to mid-70s Fahrenheit. That said, some mosses do seem to adapt to higher temperatures. Some, in fact, such as Java moss, will tolerate a wide range of temperatures with no apparent harm.
Provide a surface. Mosses tend to grow more quickly and with a more compact, bushy growth when their rhizoids are given the opportunity to attach to a rough surface, such as rocks or driftwood. It is possible to simply put both moss and surface together in the same aquarium and wait — some fronds will eventually find the surface and attach to it. However, there are more straightforward and efficient ways to accomplish this. It is best to spread the moss in a thin, even layer over the surface, which will ensure maximum coverage of the surface and thickest growth when the moss begins to grow out.
As for attachment, you may use a length of fishing line or black thread. Once you have distributed the moss over the desired surface, simply wind the line gently around the rock or piece of driftwood and tie it off. Whether you use fishing line or thread, it will become invisible as the moss grows. Some bryophiles recommend the use of 100-percent cotton thread, as it will eventually dissolve, by which time the moss will have firmly attached to the surface. I have also used black hair nets with good results, enveloping the rock or piece of driftwood in question once the moss is arranged to my satisfaction. These seem to become invisible almost immediately, and they will soon be obscured by a carpet of moss.
A word of warning, however, is that some fish (in particular Corydoras catfish and bettas) can get caught in hairnets if they are not flush with the surface that they are used to cover.
Protection. There are some common aquarium inhabitants that will eat mosses. One of the most notorious is the Siamese algae-eater (Crossocheilus siamensis). Although I keep this species for its algae-eating propensities, I have witnessed it chewing the leaflets from fronds of Java moss. This seems to vary with the individual fish, the diet of the fish and so on, but I now avoid keeping Siamese algae-eaters with the softer mosses. Interestingly, Christmas moss, which has a harder, spikier texture than Java moss, seems not to interest my Siamese algae-eaters nearly as much.
Some report that Amano shrimp will also eat Java moss when hungry. I keep Taiwan blue shrimp with various species of moss without problems. I know for a fact that some goldfish will eat mosses, though it is possible to grow moss with goldfish, particularly when the moss is given a chance to thoroughly attach to a piece of driftwood or a stone before being subjected to nibbling.
One creature in particular that can damage moss is the freshwater amphipod, also known as the scud, side swimmer, or freshwater shrimp. When conditions are to their liking, this little beastie will nibble away at moss and reproduce rather quickly. Luckily, many types of fish find amphipods delicious and tend to keep the population at manageable levels. Basically, it is wise to be careful when introducing herbivorous species to your moss. It is wise to avoid keeping all of your eggs in one basket — try to get moss growing in various aquariums if you can. That way, if you find that your lovely mossy carpet in one aquarium has become a fishy snack, you have something to fall back on.
Light and pruning
Some of the hardier types of moss, such as Java moss, do well with ambient light, as long as it is not too dim. Betta and killifish keepers often take advantage of this fact, keeping clumps of moss in sweater boxes and fishbowls with no more than room light. Other species are a bit pickier but still do well with modest lighting — 2 watts per gallon or so. In general, the more light the moss receives, the more compact and bushy the growth pattern, though nutrients play a role here, as well.
Relating to the subject of light, the vigorous new growth in a patch of moss can and will overshadow the older growth, preventing it from receiving light. This will cause the older growth to die if the situation is not remedied. Fortunately, the new growth can easily be pruned away and used to start new clumps of moss elsewhere. This also helps prevent your patch of moss from becoming stringy.
Competitors and nutrients. Unless you are adding mosses to a high-light, high-growth aquarium or you want to encourage very fast growth, don’t worry much about fertilizer. Sufficient nutrients will come from fish waste and water changes. In fact, if there are too many nutrients for the mosses to handle, it is likely that you will find algae beginning to choke out your mosses, especially in higher-light situations.
If kept with a lot of fast-growing stem plants, though, moss may not be able to compete for nutrients without added fertilizers. If you want to keep some other low-maintenance plants with your mosses, Java ferns and Anubias are excellent companion species, as they have similar requirements and do not grow fast enough to steal all of the nutrients from the moss. An aquarium of this sort might benefit from the addition of a good trace element mix intended for use with aquarium plants but would probably get along all right without it, too. If competition with other plants or the desire for fast growth renders the use of fertilizers necessary, a formula containing iron and potassium is best. You may also want to use a trace element supplement.
Follow the directions on the bottles. The more light and the faster growth you pursue, the more tinkering you will have to do with fertilizers. This is not necessarily a bad thing, but it is beyond the scope of this article.
Supplemental CO2, as stated before, is not necessary, but I have definitely noticed an increase in moss growth rates. Pressurized CO2 systems, DIY CO2 systems and liquid carbon supplements can all provide benefits to the moss. Carbon dioxide supplementation is great, but it is a subject for another article.
Types of Moss
The bewildering array of moss species, coupled with the difficulties inherent in identifying moss, make it impossible to give anything but an introduction to a few types of bryophytes you can keep.
Java moss was long known as Vesicularia dubyana, but now there is a discussion about changing its scientific name to Taxiphyllum barbieri. In any case, this is, without doubt, the most widely known and widely kept of all aquarium mosses. There are several reasons for this. The most important may be that it is almost impossible to provide conditions under which this moss will not thrive. Not only can it grow in aquariums with high light, it can do well in aquariums with nothing but ambient light — and anywhere in between! The only fertilizer that it requires consists of the wastes that fish, shrimp or other aquarium inhabitants excrete. It will survive in a wide range of temperatures — if your fish are “happy,” Java moss will probably do fine. Otherwise, Java moss may well continue to thrive. Some fish (e.g., goldfish) will nibble on it, but it grows so well that this is generally not a problem, as long as the moss is well-established.
Java moss tends to be a bit less bushy and full in its growth habit. However, cool temperatures and moderate to higher lighting, as well as attachment to a substrate, will encourage it to adopt a more compact growth habit.
Christmas moss (Vesicularia montagnei) was named for the attractive, amazingly Christmas-treelike shapes of its fronds, which are a brighter green than Java moss. It requires a little more light than Java moss, but I have had it do well in slightly less than 2 watts per gallon. When handled, this moss is firm and a bit spiky. The fronds tend to grow downward, making for a very attractive effect when attached to driftwood.
All mosses will vary in growth habit, color and other characteristics, depending on environmental conditions. Yet Singapore moss, the true owner of the scientific name Vesicularia dubyana, seems to vary widely in growth habit based on its environment — perhaps even more so than other mosses. This species has leaflets that are shaped similarly to those of Christmas moss, but the fronds are usually less regular. Despite this, it is still a very attractive moss to keep.
New and exotic forms. It seems that new and exotic forms of moss are appearing all the time, with bizarre shapes or growth habits. Peacock moss, for example, grows in angled mats said to resemble the tail of a displaying peacock. Dragon ball moss sports large, round sporophytes that give it its fanciful name. Flame moss has a growth habit that — you guessed it — resembles flames, while stringy moss is, well, stringy. If these creative appellations intrigue you, look to the Internet to get more information on them.
Mystery mosses. Lastly, we’ll examine the mystery mosses. These are mosses that show up unexpectedly, as my first aquatic moss did, or those that are mislabeled by the seller. I recently purchased a beautiful, bushy moss that was erroneously labeled “Java moss,” though I am quite certain that it is not Taxiphyllum barbieri — I suspect it is actually Singapore moss.
Propagating moss is the easiest process you can imagine. Simply remove a frond or fronds from one location, and place them or attach them in another. Voila! The moss does the rest, attaching within a couple of weeks and getting down to the business of growing.
By and large, those of us who are not bryophytes by profession cannot hope to identify these mystery mosses unaided. There are some good resources to help those who wish to try, such as aquamoss.net. Since mosses do tend to have similar requirements, if we happen upon a mystery moss that we like, we can usually provide it with what it needs and enjoy its unique beauty, regardless. Sometimes, ignorance can still be bliss!
Delaney McCullough, Ms. Mary Elger- Lonzarich, Dr. Joe Rohrer, and Dr. Dave Lonzarich – A Preliminary Study of Deep Water Aquatic Mosses
Leong, L.K. 2004.“Mosses and the Men Who Love Them.”