Anemones

A recent Salt Solutions addressed a readers question of which anemone to provide for an assortment of clownfishes. The response explained that many clownfish species are relatively anemone-specific and that an effort should be made to match the anemonefish to the correct host anemone. The response concluded with “Normal flourescent lighting is usually not adequate to maintain anemones for the long term. VHO, compact flourescent, or metal halide is recommended if you want to see your anemones flourish. If this type of lighting is not available to you, our suggestion would be to pass on the anemones and keep just the clownfish.”

I was very glad to see that last sentence, but I would like to take it a little further. Despite the fact that I, and many of my friends and colleagues were lured into starting marine aquaria by the fascinating relationship between the clownfish and their host anemones, I generally try to discourage most hobbyists from ever purchasing one for their reef aquarium. Part of the problem is that the majority of these anemones are not really "reef" animals in the typical sense of the phrase, and part is that husbandry of anemones is poorly understood. Despite the frequency with which I have overheard an employee in a petshop claim that "anemones are hardy animals that are easy to keep," I feel that many aquarists are mislead into thinking that anemones are appropriate for even a beginners reef tank. This couldn't be further from the truth, and I will try to explain some of the reasons why.

First, although the anemones that host clownfishes typically harbor photosynthetic algal symbionts (zooxanthellae, zoochlorellae, etc.), and algal production in intense light appears to be the major source of energy for anemones, all anemones require some animal prey for long-term survival. The shape and behavior of tropical host anemones both serve to increase the amount of area available for "harvesting" sunlight, and with few exceptions, intense lighting (typical of coral reef tanks) is required for anemones gain sufficient energy for survival (as was pointed out in the original response). Some species of host anemone are found exclusively in very shallow water and only in areas that are directly exposed tp sunlight (e.g., Stichodactyla gigantea), while others can sometimes be found in shaded areas, or even deep water environments (e.g., Entacmaea quadricolor). Depending on the habitat from which the animals were collected, very different levels of lighting may be required to maintain them successfully. However, I disagree that having VHO or metal halide lighting is the key to maintaining an anemone. Even in tanks with intense metal halide lighting in which stony corals are thriving, anemones are often reported to bleach and wither -- whether this is a result of too much light for a low-light adapted animal or a sign of other stressors is simply unknown. Furthermore, despite the fact that anemones look to be helpless predators just waiting for something to blunder into their waiting tentacles, most species appear to be prey specialists, and require both specific mechanical and chemical cues for the discharge of their cnidae (specialized stinging cells that anemones use to capture their prey). The cues required and the venom that is associated with these stinging cells both differ by species, and -- just to make things more complicated -- also differ depending on the condition and hunger of the animal tested. To date, there has been no cnidarian (the group to which anemones and corals belong) discovered which is capable of obtaining 100% of their nutritional requirements from light alone. All cnidarians (the group which includes hard and soft corals, anemones, gorgonians, mushrooms, jellyfish, hydroids and the like) require some food to survive, and in some cases the output of photosynthesis has been shown to depend on “fertilization” by the animal ingesting prey. If the animal has specific feeding or prey requirements, it makes the job of maintaining them in an aquarium that much more difficult. Anemones seem to fall into that category, and there are foods that are readily accepted by one species that are basically ignored and dropped by others. To make this problem more difficult, different aquarists report that their anemones eat different foods this could mean that the animals have been misidentified and are not actually the same anemone species, or (more likely) that prey preference and feeding requirements differ depending on the animal in question and the conditions under which it is kept.

Secondly, and perhaps most discouraging is that these animals are essentially immortal in nature. They certainly appear capable of living several hundred years (yes, you read that right -- hundreds!), and do not seem to age in the way with which we are accustomed, but rather likely live on until disease, a predator or some natural disaster kills them. Despite their natural longevity, the life span of the vast majority of captive anemones is less than a two years. A recent survey of reefkeepers conducted by Joyce Wilkerson found that among a couple hundred respondents only 5% of hobbyists with 2-5 years of reef keeping experience had managed to keep their anemone alive for 2 years or more (this survey was specific to the clownfish/anemone host species Entacmaea, Heteractis, Stiochodactyla, Macrodactyla & Cryptodendrum). That's not very encouraging is it? To make it worse, among hobbyists with less than 2 years of experience, nearly half of the anemones purchased were dead within 3 months -- overall only 1 in 13 anemones survived for 3 years or more and only 1 in 32 anemones survived for 5 or more years in captivity (which by most accounts is considered a great success). Even if we consider 5 years to be a ripe old age for these animals in an aquarium (this is roughly the equivalent of considering rearing a human being to 1 year as being a "success"), only 3% of anemones purchased ever make it to this age (and if you are familiar with the mortality suffered in transport, you should begin to realize that a large percentage of "difficult animals" do not survive long enough to make it home into an aquarium). This survey included many highly experienced and profession reef keepers, but despite the general expertise of the people who participated in the survey, only 5% of people can keep an anemone alive for more that 2 years! That is pretty abysmal for an animal with a natural life span of hundreds of years; especially given that, according to Daphne Fautin (famous anemone biologist and author), removal of these anemones and their clownfishes is causing serious changes in the natural communities that she studies. In their book, Fautin and Allen mention that some populations they once studied in the Philippines have become extinct as a result of collection and the habitat destruction associated with dynamite/cyanide fishing.

Third, many of the host anemone species (in particular several of the Heteractis, Macrodactyla and Stichodactyla species) are not generally found on the "reef" itself. Even with those species that do commonly occur living in close association with stony corals (e.g., H. magnifica, Stichodactyla mertensii and Entacmaea quadricolor), tank conditions that support excellent coral growth do not seem to support long-term survival of the anemones. Given that many reef-living anemones do not seem to flourish in reef tanks, it is not at all surprising that species living predominantly in soft sediments adjacent to reefs (e.g., Heteractis aurora, H. malu, H. crispa, Stichodactyla haddoni, S. gigantea, and Macrodactyla doreensis) rarely flourish in reef tanks. Aside from habitat differences, conditions of flow, lighting and food apparently required by anemones may differ from those required by corals, because anemones often bleach and wither in tanks within which corals are thriving and even reproducing. There have been a number of theories as to why the survival of anemones in captive aquaria is so low, including lighting, feeding, flow, typical nutrient loads and the list goes on, but the truth of the matter is that no one really knows. If anything constructive came out of the anemone survey, it is that every aquarist who had accomplished the feat of keeping an anemone for 3 years or more had a different explanation for their success. Lighting type and intensity, food type and feeding frequency, tank size, conditions and everything else questioned seemed to differ among the successful respondents, and there were no clear patterns that Joyce could pull from the responses she got to her survey. There do not seem to be any easy answers to specifically what people are "doing right" although there were many things that unsuccessful people are likely doing "wrong" with these animals (such as not feeding them or keeping soft-sediment species in a Berlin-style reef tank).

Recent research has shown that clownfish have an odd variety of innate and behavioral protection from contact with the host anemones, and that both species and developmental stage are important in determining which anemones prove suitable for which clown species. For example, regardless of natural association, researchers found that the eggs of all clownfish species (both Amphiprion and Premnas) were unharmed by contact with any host anemone, but the larvae of every species were captured and eaten by every anemone tested. Innate protection appears to begin at settlement, and once larvae metamorphosed into juvenile clownfish, there are species-specific patterns of host immunity to the sting of various host anemones (as explained in Salt Solutions). However, in most cases the fish are also capable of a behavioral adaptation to a given host, and those fish that survived the initial contact typically adapted to whichever anemone present. The exception was the carpet anemones – Stichodactyla spp. – which are fish predators and have such a powerful sting that if the juvenile fish were not protected from it with an innate defense, they were usually unable to break free and were ingested rather than developing a behavioral defense from the anemone. The most specific association of anemonefishes and their hosts appears to be the Maroon or Spine-cheeked Clown (Premnas biaculeatus) with the Bubble-tip anemone (Entacmaea quadricolor ). As it turns out, all clownfish species tested were capable of contacting the tentacles of the Bubble-tip anemone without being stung as soon as they metamorphosed into juveniles, but Premnas was incapable of developing a defense to any other species of anemone tested. It is likely that the association of most clownfishes for a specific host anemone in nature is a function of an interaction with ability to adapt and the host use of other clowns in the region. The fact that both innate and behavioral protection is possible, and that the level of protection differs at different stages of the life of the fishes only adds to the existing confusion about exactly how and why the association between clownfishes and anemones has developed. In fact, the "rules" of host preferences and associations often seem to break down in aquaria, and it is common for a pair of clowns to spend all their time in a long-tentacled plate or leather coral or some other such "inappropriate host" despite an available anemone of the "correct" species nearby.

That brings me to my last point. The majority of clownfish sold in the pet trade today are captively raised and even wild caught ones do not NEED an anemone. Juvenile survivorship is significantly higher when associated with an anemone in nature (in order to survive heavy predation on newly settled fish), and the anemones do much better with the clowns to protect them from attacks of butterfly fishes, but at the size that clowns are sold for the pet trade (and especially in the absence of the typical suite of predators), clowns have absolutely no requirement for anemones in a tank. Of course there remains the aesthetic lure of watching a pair of clownfish snuggled into their anemone home, and that is as good a reason as any other to want an anemone for a tank, but realize that the anemone is being added for the sake of the viewer rather than the clownfish themselves.

The reason that I felt obliged to write this expansion on the response offered in Salt Solutions, however, is that like most published responses to questions about anemones in captivity, we failed to mention the extremely low rate of success with these animals in aquaria. I think that it is only fair that anyone considering the purchase of one of these animals be aware of the likelihood of success at keeping it alive. On average, that success rate looks about 1 in 32... Not great odds for an expensive animal which is exclusively collected from the wild, and whose import is leading to habitat shifts in natural communities!

Most of the people of whom I know who have long-term (again this means only 5 years or so) success with anemones maintain them in a tank specifically designed to meet the needs of the animal, and in which the introduction of corals and other invertebrates is of little or no concern. If you intend to set up an aquarium with the specific goal of keeping anemones (with or without clownfishes), and gear the tank design specifically to that goal, I think that is great. As always, I encourage people to research the needs and natural habitats of the animals extensively, and to search out those rare pet shops that will be honest and informative (by which I mean somewhat discouraging) on the success rate of the average aquarist in keeping these animals. If you walk into a petshop and say "I want to add a Sebae anemone to my tank for my clownfish," and they show you to a tank of partially inflated white anemones and reply anything like "No problem, they are hardy and easy to keep," I would recommend that you find a shop that provides you with much better guidance. The initial condition of the animals is a large determinant of how successful you are likely to be, and an animal that is already bleached (again, these animals gain much of their energy from photosynthetic symbionts, and you have never seen a white tree with purple tips to the branches for a reason) the chances of it surviving in your aquarium at home is even lower than the terrible statistics I included above.

Considering the confusing nature of the relationship between clownfishes and their anemone hosts, the apparent specificity and diversity of natural anemone diets and lighting requirements, the non-reef habitat preferences of most anemones and the fact that a pitiful 5% of even experienced reef keepers have managed to keep one of these anemones alive for more than 2 years (substantially less than 1/100 of their potential natural lifespan), I hope that readers will heed the advice given in the last sentence of that Salt Solutions response: “pass on the anemones and keep just the anemonefish.”

For readers that really want to keep an aquarium with a host anemone, I suggest you seriously consider whether your aquarium and ability are right for these animals. If you decide that you are up to the challenge, I hope that you will research the needs of the animal and design a tank around providing for those needs so that your next anemone will be your last – if properly cared for and allowed to live out its natural life span, these animals should become a family heirloom that should out-live not only you but likely your children and possibly your grandchildren. Until we reach the point where these amazing animals are routinely surviving for more than a couple of years in captivity, responsible aquarists should resist the temptation to buy them -- no matter how beautiful and fascinating they are.