AHABS... Issue Eight
Sea Anemones: The Husbandry Of Deceptively Simple Animals, With Discussions Of Their Natural History, Physiology, And Reproduction
Ronald L. Shimek, Ph. D.
What is probably the most common icon of coral reefs doesn't show coral reefs at all; rather, it is and image of clownfish nestled snugly in their host sea anemone. An image of almost palpable “cuteness,” I would hazard the guess that it is additionally, and not coincidentally, in one form or another probably the single most used marketing image on hobby paraphernalia. The nestling behavior is something that I think every marine aquarist – and I dare say, every marine biologist J - has thought they would like to see in their aquaria at one time or another. Unfortunately, while the care and comfort of clownfishes is easily accomplished, see Wilkerson, 1998, long-term maintenance of the sea anemone hosts has seemed to be beyond the grasp of many aquarists. Although sea anemones are “simple” animals, successful and long-term care of most host anemone species is quite beyond the capabilities of most hobbyists. Only one host anemone, Entacmaea quadricolor , is “easy to keep,” and even that “ease” is deceptive. There is nothing inherently difficult about keeping these animals, yet their mortality rate in home aquaria is awesomely high.
I have worked with and done research on sea anemones since the mid-nineteen seventies. I have kept several individuals of a couple of large temperate sea anemones species ( Cribrinopsis fernaldi ; Urticina crassicornis ) and had them spawn and have successfully kept the larvae until they metamorphosed, and then raised the juveniles for periods of up to a couple of years. That work was more-or-less completed by 1990. Since then, most of the anemones I have kept have been tropical species including some individuals of several clownfish “host” sea anemones. I have been successful enough at keeping them to have a few of them grow and spawn while under my care. To be fully honest, in trying new and various techniques and methodologies, I have also, regrettably, inadvertently killed a relatively large number of them. By killing some of them, I have found some things that don't work, and by successfully maintaining most of them, I have found out how to keep them alive and well. Some of the things I have found out about them that are not intuitively obvious, including techniques of various aspects of their care. Hopefully, by explaining the techniques involved with their care, I can also explain some facets of care that, although they may seem logical, simply don't work. With some luck, perhaps you will not have...
Ronald L. Shimek, Ph. D.
While soft corals, corals and sea anemones are categorized together in the Class Anthozoa of the Phylum Cnidaria, and animals in all of these groups have a lot in common, the differences between them are also profound and have significant repercussions with regard to the biology of the animals. How different are these animals? Well, from the examination of differences in the basic genetic material of these two groups, it appears that they last shared a common ancestor about 400 million years ago, and that is plenty of time for major differences to develop. As a comparison, the common ancestors of both present-day reptiles and mammals lived about half as long ago, so as a comparison, the avian dinosaurs are a lot closer relatives to you, than soft corals are to sea anemones. So, yes they all are Cnidarians. But, no, kissing cousins, they are not.
The basic bottom-dwelling body form in all cnidarians is that of a polyp, described in detail in the sea anemone article in this issue. Naturally, all soft coral bodies are derived from the standard polyp, although in some of them the basic shape may be very obscure (Kozloff, 1990; Ruppert et al, 2003).
Anemones, sort of…
Soft corals are anthozoans, and share many characteristics with the sea anemones. Both types of animals lack a free-swimming or medusa stage, and they both possess a pharynx, and a siphonoglyph, the ciliated groove down the length of this pharynx at one end of the slit-like mouth. As with the other cnidarians, the soft coral body wall consists of three layers: an exterior layer of protective epithelial tissue called the epidermis, an interior layer of a digestive epithelial tissue called the gastrodermis, and a relatively thick fibrous layer that lies between these two tissues. This connective fiber layer, the mesoglea, is primarily composed of proteinaceous fibers, mostly made of collagen fibers (the same material that constitutes tendons and ligaments in mammals - gristle!), although there are significant amounts of other proteins as well. Collagen is non-elastic and not extensible and its presence in the soft coral body walls allows them to resist deformation and maintain their shape. Many of the soft corals are naturally found in shallow water environments that have significant wave action and turbulence. The presence of such a rugged fibrous mesoglea has been shown to be a significant factor in the ability of many sea anemones to live in wave swept areas, and it is probably just as critical with the soft corals...
Penning A Story
Ronald L. Shimek, Ph. D.
Aquarists often assume that research has been done on all types of marine animals; in reality, the actual body of information concerning these creatures is vanishingly small. This is particularly true of coral reef animals, where what is not known far out weighs what is. While coral reefs have been known as long as there has been somebody around to fish on them, scientific research on them has been a very recent endeavor, indeed. The first ecological research on coral reefs was done in the 1920s, but strange as it may seem, very little additional work was done over the next 30 or so years. Research on Caribbean coral reefs really didn't start until the late 1950s, and as recently as the 1970s, the number of people actually out in the field doing scientific investigations would not fill a small meeting room. The reasons for this odd situation are primarily logistical. In general, the ecological sciences developed in England , the United States , Canada , and the northern European countries. Coral reefs are distant from these countries, expensive to visit and relatively difficult to study. For reasonable ecological research to occur, the investigator needs to be on the site for extended periods. Shallow water marine environments of all sorts had to await the development of some sort of equipment to allow the researcher to be on location for extended periods. The necessary equipment in this case was SCUBA (an acronym for Self-Contained Underwater Breathing Apparatus). It wasn't until the late 1960s until a few scientists began using scuba as a research tool. Even then, because of the expense in getting there, coral reef areas were not extensively studied.
Simply doing underwater research is far more difficult than most non-divers can imagine. Unless one work regularly in such environments, it is hard to comprehend the problems inherent with moving in a viscous medium where even at the best of times one can only see a limited distance and where currents and surge can make even the taking of notes difficult. Additionally, the necessity of breathing pressurized air in a high pressure environment severely limits the time on site. For underwater research, the dollars per datum ratio is very high; or put another way, an underwater researcher doesn't get much bang for the buck. Most in-depth ecological research is done by graduate students as part of their, primarily, doctoral research programs. Such programs are often designed to last several years and provide a significant body of information. However, due to the nature of funding agencies, such studies are often run on quite limited budgets. All of these constraints have 1) made it very difficult for decent long-term underwater water ecological research of any sort to occur, and 2) when good projects are carried out, they are generally done in close proximity to a marine laboratory. Most marine labs are in temperate regions distant from coral reefs, and this is where most marine ecological research occurs. Until very recently, say the last 15 years or so, most ecological research carried out on coral reefs was in the nature of short...