by Rob Toonen
There can be little doubt that the keeping of saltwater tanks has changed considerably over the past 30 years. The development of techniques and technology to aid in maintaining sufficiently high water quality, moving water in aquaria to provide acceptable circulation, and providing adequate light for photosynthetic corals has fundamentally changed the way that hobbyists today think about keeping marine organisms. The release of an issue of TFH dedicated to looking back on some of the multitude of changes that we’ve seen in the hobby for keeping certain groups of animals in captivity really helps to illustrate how far we’ve come, while at the same time hopefully reminding us of how far we have yet to go. I’m sure that I don’t have to remind anyone who has been reading my column for a any length of time that there are still many animals that do extremely poorly in captivity, and I have advised against the purchase of many of the unusual invertebrates that people have asked me about over the past couple of years.
So, despite the fact that we have a long way remaining in our journey to provide more realistic and healthier homes for our aquarium pets, we can also celebrate the fact that we have come a long way. In this article, I wanted to do something a little different for a change, and following on the discussion of the techniques for captive breeding we just finished, I wanted to talk about the ingenious people that pioneered the captive culture of marine invertebrates in captivity.
Until the last twenty or thirty years, keeping the vast majority of corals was considered difficult to impossible by the majority of marine aquarists. There was certainly some limited success with tropical reef fishes even then, but at that time the long-term survival of coral reef invertebrates in the aquarium was something that was an unusual accomplishment. Certainly the days of metal-framed aquariums filtered by a floss-filled corner filter, and lit with incandescent lights did little to improve the success rates with these delicate animals. I can still remember the pride expressed by the owner of the local shop that first got me into saltwater tanks when he showed me his aquarium that was filled with tiny Aiptasia anemones. It may seem ridiculous by today’s standards, but in the early 70s in northern Canada, even getting Aiptasia to survive in captivity long enough to reproduce was somewhat of an accomplishment.
Now, with the widespread availability of high quality artificial salt mixes, pumps that can turn over large aquaria several times each hour, highly efficient protein skimmers, and lighting that can approach the intensity and spectrum of natural sunlight, the basics for keeping corals in the aquarium seem pretty simple by comparison. In addition to the advances in equipment, there have been some very important advances in the techniques and attitudes towards livestock in coral reef tanks. One of the most encouraging to me is the emphasis on more natural systems common among modern reef enthusiasts. Live sand and/or live rock are widely available and widely used in the hobby, and are considered the basis of biological filtration for the majority of reef aquaria. Live rock is quite simply chunks of rock (quite often coral rubble) that have been farmed or harvested from the ocean with various species of encrusting and burrowing organisms attached to them. These rocks provide a wide variety of organisms and a more natural and realistic background for the placement of corals in reef aquaria, in addition to their important function of biological filtration. Likewise, the bacteria and organisms present in live sand can be an important component of a reef aquarium, by functioning in both a filtering capacity and by providing an important source of food to corals in the aquarium as the worms and other organisms in the sand reproduce and release their free-swimming larvae. Although fads and preferences change through time, and there are many equally successful ways to set up a reef aquarium, I would hazard to guess that the use of live sand and/or live rock in conjunction with the technological advances in artificial salts, protein skimming, water movement and lighting are largely responsible for the widespread success of so many marine aquarists today.
I know that many aquarists have debated who was the first person to come up with the idea of maintaining a “miniature balanced ecosystem” (in which the goal is to set up a balanced aquarium with natural sand and rock used to provide filtration for a group of animals maintained in the aquarium). Contrary to the popular aquarium lore, I will argue that the first person to develop an aquarium based on the use of live sand was Caswell Grave, who published his findings on the use of live sand in an aquarium in 1902. Grave was trying to figure out how to raise sand dollars in captivity, and although he was able to breed them, he was having a hard time providing food for the baby sand dollars. He solved that problem by dredging a liter of live sand from the ocean floor, and setting it up in a small outdoor aquarium. He allowed the growth of a dense diatom film on the sand that he had collected, before setting up several 1 liter aquaria with clean water and added a thin layer of diatom-coated sand to each of these tiny tanks to provide a sandbed in which the baby sand dollars could settle. Larvae were then added to these tiny tanks and covered (to minimize evaporation, I would presume) before being set in front of a window where they received plenty of indirect sunlight (direct lighting could cause the tanks to overheat). Using this method based on the use of live sand in his culture tanks, he succeeded in raising several baby sand dollars in captivity for the first time in the early 1900s (Grave 1902).
Although this method obviously worked to raise a few baby sand dollars, there was a fair bit of uncertainty involved, because the conditions were never likely to be exactly the same in each tank that was used. For example, one never knew which species of diatom would grow, whether there were other organisms in the collected sand that may compete with, or prey upon the babies, etc. Researchers wanted a method of obtaining and feeding pure cultures. Because sterile techniques had already been well established for bacterial research by the turn of the century, it was simple for researcher to adapt these techniques to the culture of marine invertebrates in captivity, however they were not widely applied to larval culture until the 1930's. The original method was suggested by Miquel (1897) and modified by many thereafter (e.g., Allen & Nelson, 1910; Gran 1932, Waksman & Iyer, 1932). The basic technique researchers used involved adding certain nutrients (potassium nitrate, calcium chloride, sodium phosphate and ferric chloride) to seawater, sterilizing that enriched seawater and inoculating the nutrient medium with a single species of diatom. Other researchers (e.g., Schreiber, 1927) quickly discovered that modifications of the basic recipe led to increased success with culturing certain species of phytoplankton (e.g., the addition of potassium silicate to diatom cultures).
Obtaining sterile, enriched seawater turned out to be the easy part, however. Early researchers did not have any source from which to order stock cultures of a specific species of phytoplankton, nor did they know which species were good or poor food choices for various larvae; they were forced to use trial and error to collect phytoplankton to culture, and then determine how appropriate that alga was for culturing various animals. The methods used by these early researchers to isolate algae were simple, but turned out to be quite effective. The first was to simply look under a microscope and pick a single cell of a likely candidate alga from a natural collection of seawater. Assuming that the cell lived and started to divide, these cultures would be grown up and could then be tested for suitability as a food item. Another method involved placing a drop of natural seawater into a large dish full of enriched sterile seawater. This drop would be well mixed, and then the dish would be kept under subdued light in an area where it could be examined with a hand lens without moving or disturbing it. As soon as spots of different phytoplankton colonies could be seen growing in different parts of the dish, a small sample of each would be removed with an eyedropper and transferred to fresh culture medium. In this way researchers could obtain many cells of the same species to innoculate a culture and eliminate some of the variability involved with starting a culture from a single cell (which could easily be lost or killed in the transfer). Some fairly elaborate modifications of these methods were developed by subsequent researchers in order to eliminate as many bacteria, ciliates, flagellates and other microorganisms as possible from the phytoplankton cultures. These advances eventually culminated in the recommendations of Guillard (1975) which became the standard technique used in most modern phytoplankton culture research. Despite the fact that these methods are well-established and culture of phytoplankton is cheap, they are work-intensive and difficult without the proper facilities (see Toonen 1998 for details). Today, however, thanks to a number of vendors selling pure cultures of phytoplankton, we fortunately have the ability to easily purchase phytoplankton stocks, and the home aquarist doesn’t have to worry about such problems.
But Graves was not the only person to be having success with marine invertebrates way back then. In 1894, Wilson was the first to report successfully reproducing sponges in captivity. Because sponges brood their babies within the body of the parent for some period of time prior to the release of planula larvae, Wilson (1894) simply placed reproductive sponges into a jar and collected the larvae as they were released. Planula larvae of sponges are well-provisioned with yolky nutrients, and do not need to be fed, so it was relatively easy to keep the larvae until they settled and began to grow into tiny sponges. He kept the sponges in unfiltered jars on the shelf in his lab, and changed the water 2-3 times per day to keep the animals healthy. Not only did this simple strategy work, but the sponges grew to maturity, even started to reproduce on their own in the lab several years later. Wilson reports having a captive-bred population of sponges in 1907. Not too bad at all for a guy raising sponges in some empty pickle jars in 1907, especially considering how often I get requests for people asking me how to keep their sponges alive today!
I must admit that it is always somewhat surprising to me that early researchers had such success with breeding these animals when it seems that even with the amazing array of advanced aquarium technology and techniques available today, few people have this level of success with breeding their marine invertebrates at home.
Much to my surprise a number of cnidarians (sea anemones, corals and jellyfish) were also among the first animals to be raised successfully in captivity around the turn of the century. Despite the fact that success with corals in captivity was exceedingly rare until twenty or thirty years ago, Thomas Wayland Vaughan appears to have been able to breed and raise corals in the early 1900's (Vaughn 1919). Granted, he was in the Tortugas, and was close to a natural reef and source of natural sea water, but that doesn’t really take away from his accomplishment of having corals spawn in his holding tanks and raising the larvae. His paper (published in 1919) reports that he managed to breed and raise the planula larvae of five species of corals (Astrangia solitaria, Favia fragum, Agaricia purpurea, Porites clavaria, and Porites asteroides) in 1908. Not only did he breed and settle them, but he actually succeeded in keeping the newly settled colonies of Favia fragum and Porites asteroides alive from larvae through settlement and five years of subsequent growth (some reached nearly 10 cm in diameter during that time), which was a remarkable accomplishment for the time.
For those of you that don’t think keeping a coral colony alive for five years is such a remarkable accomplishment, let me put it to you this way: even with the bewildering array of gadgets and techniques available to reef-keepers today, I would hazard to guess many people could not boast of five years of growth among most of their corals. Even more, how many of us can boast of having bred and raised any coral in captivity? Now imagine that I took away all the fancy equipment that most tanks today run on (such as the protein skimmer, lights, pumps, etc.). Because he had none of the modern technology that many of us take for granted today, Vaughn was forced to set up a siphon system in which “stale water” was drawn off the top of his tanks and “fresh seawater” was replaced via a gravity feed from a container suspended above the culture aquaria to maintain water quality. Vaughn also lacked any high output lights, and was therefore forced to rely on the indirect sunlight provided by a nearby window to light his tanks (direct sunlight led to overheating of the aquaria). Given the conditions under which he had to raise these animals, I think that the culture of corals from larvae through five years of growth into nicely sized colonies suddenly becomes an accomplishment that we must all acknowledge.
I hope that this little trip down memory lane will help put into perspective the relative accomplishments we have had in the marine aquarium hobby over time, and also emphasize what can be accomplished with a little ingenuity and a lot of attention and effort. In the case of corals raised in the early 1900's, Vaughn had none of the equipment we have come to consider “necessary” for successful culture of corals, and yet had more success with the animals than many of us have today. To me, that is a good lesson in what is really “necessary” to maintain a salt water tank - a lot of care, knowledge and dedication. All the equipment and technology available today cannot save a poorly conceived or cared for system, and yet someone without any of it was able to breed corals in 1908.
I wanted to conclude by saying that I am not in any way trying to encourage people to do away with all of their aquarium technology. As I said at the beginning of the article, I really do think that the use of live sand and/or live rock in conjunction with the technological advances in artificial salts, protein skimming, water movement and lighting are largely responsible for the widespread success of so many marine aquarists today. In my opinion, the reason for this level of success is not that such equipment is absolutely necessary for the maintenance of coral reef invertebrates, but rather that it increases the margin of error possible in a coral reef aquarium before there is a catastrophic failure that results in the loss of the animals. There are a few individuals that are really good at setting up and maintaining reef tanks that can, and do, succeed with very little equipment on their tanks. But there are many more who cannot accomplish that feat, and for the average aquarist, a well-planned aquarium based on live rock and sand, a protein skimmer, good pumps and lights will certainly make keeping corals alive in the aquarium considerably less risky. Considering how much time, effort and money are invested into a reef aquarium in the first place, these items seem like a reasonable foundation to any reef aquarium, and I think we owe it to the animals that are brought into our care to give them the best possible chance at survival...
Allen, E.J. & E.W. Nelson. (1910). On the artificial culture of marine plankton organisms. J. Mar. Biol. Assoc. 8:421
Grave, C. (1902). A method of rearing marine larvae. Science 15:579
Gran, H.H. (1932). Phytoplankton methods and problems. J. du Cons. Internat. pour l'Exploration de la Mer. 7:343
Guillard, R.R.L. (1975). Culture of phytoplankton for feeding marine invertebrates. In: W.L. Smith & M.H. Chanley (eds) Culture of Marine Invertebrate Animals. Plenum Press, New York, NY. p.29
Miquel, P. (1897). De la culture artificielle des diatomeès. Le Diatomiste 1:73; 93:121; 149:165
Schrieber, E. (1927). Die reinkultur von marinem phytoplankton und deren bedeutung fü die erforschung der prouktions fähigkeit des meereswassers. Wiss. Meeresuntersuchungen Abt. Helgoland, 16,10:1
Toonen, R. 1998. Green Water: The Culture of Marine Phytoplankton. Reef Aquarium Farming News 13:2, Jan. (http://www.garf.org/news13p2.html)
Waksman, S.S. & K.R.N. Iyer. (1932) Synthesis of a humus-nucleus, an important constituent in soils, peats and composts. J. Wash. Acad. Sci. 22:41
Wilson, H.V. (1894). Observations on the egg and gemmule development of marine sponges. J. Morph. 9:277
Wilson, H.V. (1907). On some phenomena of coalescence and regeneration in sponges. J. Exper. Zool. 5:245
Vaughan, T.W. (1919). Corals and the formation of coral reefs. Smithsonian Inst. Publ. 2506, Report of 1917. p.189