Cleanup in Aisle Three: Marine & Reef Janitors Part 1Author: Kieron Dodds
There was a time when we could barely keep fish alive in marine aquariums, and even then there were only a few bulletproof species, like the various damselfishes. At that time, you could find the occasional octopus offered for sale, or perhaps a sea star species or two—but in today’s hobby, the story is very different. While available fish species certainly outnumber the list of motile invertebrates regularly offered for sale, there are still dozens of invertebrates to choose from. Unfortunately, care information and species descriptions can be lacking at the points of purchase. To make matters worse, many sellers of such animals will recommend inordinately large numbers of these organisms. Of course, we’re not discussing anemones, corals, or ornamental crustaceans. What we’re talking about are organisms that are used to lessen the aquarists’ burden—those used to clean the tank. These can be consumers of all forms of detritus (from uneaten food and fish waste to the exudates of other organisms), algae grazers, or even some of the few organisms that are known to consume cyanobacteria.
Introduction to Cleaners
These organisms are collectively lumped into a group of very dissimilar phyla and families and are called janitors, cleaning crews, or other marketing names. Unfortunately, these names often detract from the organisms themselves and can even create problems and unnecessary expenses for the aquarist. First, I believe it is important to establish what it is we actually expect these creatures to do and how we expect them to further our enjoyment of the hobby. After all, if they just take away from our enjoyment—directly or indirectly—why would we want to include them in our aquaria? That’s a very good question, and one you will hopefully find the answers to in this article.
There is a tendency within our hobby to group these organisms together based on what they are believed to consume. For example, you will sometimes see packages of these organisms offered for sale to consume detritus or algae. That’s a fair enough distinction, assuming that the animals sold in the packages do actually consume what they are advertised to consume. Sometimes this is the case, but sometimes it isn’t.
The beginning of our understanding then needs to address what we need to control, how it gets there, why it continues to be a problem, and what the possible solutions are. These things may be easy to understand, but they’re not always easy to accept. Without nutrients available for their growth, nuisance organisms (the kind we’re trying to get rid of, often being algae and cyanobacteria) will not survive. Removing detritus in some way before it is available to these nuisance organisms is one approach to controlling or eliminating them. However—and this cannot be stressed enough—the nutrients that are consumed by detritus feeders are not removed from the environment. They are sequestered in the biomass of the detritivorous organisms, or excreted in the waste products of those organisms. For all intents and purposes, detritus is never really removed from the aquarium when using detritivorous organisms—it is simply converted into other forms.
Therefore there are still some nutrients available, and also, the detritivorous organisms won’t live forever either, so the nutrients sequestered by them will once again become available at some point in time. This nutrient availability can still fuel algae and cyanobacteria blooms. Controlling these nuisance organisms through direct predation is another tool used by aquarists. But keep in mind that some of these organisms are not consumed by predators—at least not the predators we keep (or can keep). Furthermore, they often grow faster and spread more rapidly than they can be consumed by most invertebrate predators.
Improper Stocking Rates
Assuming that the packs you purchase are collections of organisms that actually consume what they are advertised to consume, you may find that the problem is still not being brought under control. The resulting tendency would be to purchase more of them, but that is not necessarily a good idea, and there are many reasons why.
For example, astraea and turbo snails (Astraea spp. and Turbo spp.) are often purchased with the intent of controlling algae. They do eat algae, but only algae films, and in very little amounts, in a line to wherever they may be traveling. The practical result is that mats of hair algae like Derbesia spp. and Bryopsis spp. are not brought under control by these snails. Furthermore, if the intent is to keep the walls of the aquarium clear, the aquarist will discover that by scraping the remainder of the aquarium wall that has been only partially cleared of algae by these snails, the same surface area will still need to be covered, saving the aquarist no work at all.
Hermit crabs, which are reported to consume hair algae, will actually eat everything but hair algae. Some do consume this algae, but only as a last resort, as will some true crabs like Mithrax spp. and smaller Percnon spp. individuals. Still, these algae-eating organisms are quite small and have rather low metabolisms, thus they often cannot keep up with algae growth. In addition, many are dependent on specific types of algae to survive; if there are enough (or more than enough) crabs to eat all of the algae, they will starve.
Large numbers of snails and hermit crabs added to an aquarium will sometimes help control a problem—at first. But what happens when the problem is brought under control (as described above)? When there are no longer copious amounts of various algae species growing out of control, these cleaners will have nothing left to clean, no food to sustain them, and they’ll begin to die off. Or, in the case of hermit crabs and true crabs, the cleaners may be resilient enough to find their food sources elsewhere. Unfortunately, this usually results in their preying upon other organisms within the aquarium, including other hermits, crabs, and snails.
A Better Model
It is my assertion that including these organisms within a marine or reef tank is mostly beneficial if their numbers are kept very low. Recommended numbers often comprise 5, 10, or even 20 times the organisms that a tank of a particular size might be expected to be able to reasonably sustain long term. Keeping this in mind, the recommendations for numbers of individual species per gallon that will follow are guided by the premise that maximum diversity with minimal overlapping or opposition is a good thing. Therefore, the numbers of organisms recommended take into account that other, different organisms will be present within the aquarium in question. These recommendations are not intended to be hard and fast rules, but more as guides to help the aquarist more reasonably stock an aquarium with motile invertebrates.
Some Snails Worth Mentioning
Turbos & Astraeas
Almost every discussion of cleaner organisms will begin with snails. And any discussion on snails will usually begin with the herbivorous (or thought-to-be-herbivorous) grazing snails. Of these, the most popular snails are the Turbo spp. and Astraea spp. snails. Representatives of these genera, in the
If the tank is kept a little lower in temperature (76° to 80°F), these mortalities will usually be lessened significantly, provided that there is decent food availability. But there are better choices in herbivorous film grazers, with species that live longer and tolerate tropical reef temperatures better than the above-mentioned species. Trochus spp. and Tectus spp. are readily available, and while they may not ship as well—leading to higher initial mortalities—they tend to live quite a bit longer than turbos and astraeas in our aquaria. Currently, I have no less than a dozen of these snails in a 450-gallon aquarium, transferred over from a 180-gallon aquarium; they have been in my care for over seven years! That’s quite a long time considering that some aquarists seem to need to restock their snails every year or so.
Abalones & Cowries
There are a few other snails that, while infrequently available, are very good choices. Haliotis spp., commonly known as abalones, are herbivorous grazers that feed on films and diatoms. Their initial acclimation can be a problem, and they do require full-strength salt water. They are also infrequently available and expensive. In addition, some cowries (Cypraea spp.) are excellent choices not only for film algae control, but for filamentous (hair) algae control as well. Certain prejudices do exist when it comes to cowries, though, and it is important to note here that there are many cowry species that are not obligate herbivores, but corallivores, and will consume reef corals. Of the cowry species that are desirable, the most commonly available are the tiger cowry (C. tigris) and a small handful of species collectively called money cowries. Another commonly available species, or collection of species, that are worthy of discussing here are the bumble bee snails.
Bumble Bee Snails
It is reported that these snails are algae consumers, and this may very well hold true for certain species in the group. However, all of these snails are black shelled with yellow bands and virtually impossible for the lay aquarist to identify to the species level. The collection of species known as bumble bee snails definitely contains organisms that are predatory upon other snails and other invertebrates. Because it really is impossible for the aquarist to tell the bad from what might potentially be good—or at least not directly harmful—these animals should not be considered.
There are dozens of other snail species worthy of note as well; some are commonly available and some are not, while others aren’t available for sale at all, but may make it into your aquarium on live rock. Some are simply not suitable for reef aquaria for varying reasons.
Some Better Snail Choices
Taking on an algae problem directly with a biological agent alone, particularly with an invertebrate that cannot consume much, is often a futile effort. However, there are other ways to combat nutrient accumulation and the availability of those nutrients to nuisance organisms. There are several snail species kept specifically for this ability. They are detritus consumers and their performance as cleaners will go a long way toward preventing the accumulation of detritus and nutrients in the aquarium.
Cerithium spp., commonly sold as cerith snails, are one of the best choices in this respect. While they will spend much of their time in or near the sandbed consuming detritus and bacterial and algal films, they will occasionally graze algae off of aquarium walls as well. These snails will also readily reproduce in the aquarium.
Nassarius spp. and Ilyanassa spp., collectively referred to as nassarius snails, will also remain in the sand most of the time. But, like little zombies, once dead flesh hits the water (hopefully in the form of food) they will almost literally explode from the sandbed en masse and track down and consume any leftover foods. Nassarius snails will not consume detritus directly, but will consume introduced foods before they become detritus.
Other sand-dwelling species also serve to keep a sandbed clean and turned, like the algae-grazing conchs (Strombus spp.). The queen conch S. gigas gets far too large for most marine aquaria, but its smaller cousins, the fighting conchs S. alatus and S. gibberulus, are excellent algae grazers and sand turners that remain fairly small at around 4 inches. These are available as captive-bred specimens.
Of those snails that are predominantly introduced to our tanks as hitchhikers on live rock, Collonista spp. are probably one of the most frequent. Commonly called mini or baby turbos, these snails are herbivores and consume algal films and diatoms like their larger namesakes.
Stocking subtropical and temperate invertebrates in a typical tropical reef tank can be a huge and costly mistake. Not only do these organisms almost invariably die off, sometimes slowly and sometimes quickly, but the potential for fouling the water when these animals are purchased in recommended numbers for the tropical reef tank is very great. One of the biggest sellers in this respect is the margarita snail Tegula funebralis, often sold in huge numbers in algae packages. Less frequently (although still commonly) available is the red-footed moon snail Norrisia norrisii, another subtropical snail that will suffer the same fate as the margarita snail when kept in tropical aquaria. But simply sticking to tropical species does not guarantee that they are appropriate either.
For instance, the Nerita spp. snails are tropical, commonly available, and do quite well—if you can keep them in the water. These snails are tide-pool and tide-line animals that congregate in the wild in huge numbers on pier pilings and rocky surfaces near the shore. As such, they spend a good deal of time out of the water and will eventually attempt to do the same in your aquarium, spending the daytime at, near, or above the waterline. All individuals that I have kept—five dozen or so—have eventually gone overboard and been lost.
Next time, in Part 2, we'll take a look at other cleaner organisms.
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