Coralmania by Eric Borneman

It's a Small World, After All

It has been a few months since I have written a column. I have many ongoing projects that should make great reading in the near future, but none of them is completed yet, and I could not find it in me to write something about corals just for the sake of writing. This month, I choose to share briefly some of the more interesting findings I have come across during the work on some of these projects. As it turns out, the subjects all involve organisms that are very small.

Parasitic Copepods

I have recently taken a keener interest in the small red crustaceans that are associated with Acropora and which have been the subject of much discussion over the past few years. During my literary investigations into these creatures, I came across a mass of papers by Arthur Grover Humes, a copepod researcher who died in 1999 after having named some 700 new species, 140 new genera and 16 new families of copepods. His early work involved copepods that were parasitic in various marine organisms, but beginning in the 1960s, his fieldwork took him to Madagascar where he discovered parasitic copepods in corals. Over a period of some twenty years, he continued his work with corals in Mauritius, Australia, New Caledonia, the Moluccas, Enewatok Atoll, Panama, the Philippines, and other Indo-Pacific and Caribbean locations.

What is most remarkable about his work is that in reading his review publications that sometimes exceeded 50 pages each, it became apparent that virtually every coral he examined had copepods associated with it, many of them parasitic and many only associated with a single species or genus of coral. Unfortunately, as a taxonomist, he was interested more in the relationships between the copepod species than in the natural history or ecological information about the crustaceans, or how they might be parasitic. His remarks about their relationships with host corals were based on anatomical structures that are identified as being correlated with a parasitic lifestyle. For the majority of the species he described, no further work has been done to discover more of the nature of these copepods. Also interesting is how they were extracted. Humes mentions repeatedly that if one were to simply fix coral tissues with formalin, or try to dissect its polyps, the copepods would be missed, for they leave the polyp upon disturbance. It was only through careful and slow introduction of graded series of ethanol concentrations that he was able to find the hundreds of crustaceans living within the coelenteron of coral polyps or, occasionally, on their surfaces.

Scleractinian corals have more copepod associates than any other cnidarians, with species belonging to the families Anchimolgidae, Rhynchomolgidae and Xarifiidae. Some of these are bizarre looking creatures. The Anchimolgidae are exclusively associated with scleractinian corals and include at least 84 species in 28 genera. The Xarifiidae are internal parasites of both hermatypic and ahermatypic scleractinian corals (though absent in the Caribbean), consisting of another 84 species in four genera. Within the Octocorallia, the Alcyonaceans (soft corals) have the greatest number of copepod associates, and 98 copepod species are now known to occur on Indo-Pacific Alcyonaceans.

Reading this massive amount of literature on copepods made me realize two things. First, if parasitic copepods are so common in corals, what are their effects? I would suspect that no small amount of stress or mortality might occur as a result of these little crustaceans under less than ideal conditions. Second, I also learned that the red crustacean associated with Acroporids does not appear to be any of the copepods that Humes described as Tegastes and other copepods associated with Acroporids apparently inhabit the gastric cavity. I am busy at work trying to learn more about this troublesome red bug, and have enlisted the services of several specialists to help with the description of the animal, and I will write more about them in a future article as I learn more.

This crustacean has become the bane of many aquarists keeping certain species of Acropora.

Marine Actinomycetes

While working on the Elegance Coral Project, I found several papers describing the presence of a marine group of microbes within the Actinomycetes, previously well-known only from terrestrial environments. These are aerobic, gram-positive bacteria that form branching filaments or hyphae, produce asexual spores, and can even produce fruiting bodies. In many ways, they are very similar to fungi. Actinomycetes are widely distributed in terrestrial soil and are among the most important components of the decomposition pathways for organic matter. They are what give an "earthy smell" to soil. Many live in symbioses with plants, distributed near roots and rhizomes, and providing nutrients to the plants. Actinomycetes are also notable for another reason; they are one of the most important producers of medically useful antibiotics. The antibiotic, Actinomycin, for example, was one of the first antineoplastic (anti-cancer) drugs developed from Streptomyces. It is quite toxic, and besides being used in chemotherapy, is an important tool in cell biology research. I also use it in my studies on coral disease

Until recently, it was assumed that the Actinomycetes found in marine sediments were simply saline tolerant spores that had been washed into the ocean from land based sources. It is now known, however, that exclusively marine Actinomycetes are diverse and widespread. Because of the newness of this recent discovery, little is known of the biological and ecological roles of these fungi-like bacteria on coral reefs, but it is likely that they play a similar role in decomposition pathways. The antibiotic production, symbiotic nature, and decomposition aspects of Actinomycetes have interesting implications for tanks employing deep, fine sand beds. I am currently working with two marine microbiologists who specialize in Actinomycetes to determine if they have a role in the pathology of the Elegance coral, Catalaphyllia jardinei.

Actinomycetes are filamentous bacteria found in sediments that share many characteristics with fungi.

Brown Jelly Bugs

The coral malady, black band disease, consists of a consortium of somewhat variable cyanobacteria, sulfur-oxidizing and sulfur-reducing bacteria, and a mix of other microbes that form a coordinated self-sustaining band that consumes coral tissue as it moves across the corallum by the actions of sliding filaments of the cyanobacteria. The condition called "Brown Jelly" in aquarium corals appears to share many similar traits, albeit a very different appearance. I have run into a wall with regards to my investigation of brown jelly in corals. One of the difficulties of studying this condition is that it is uncommon, and consequently, it is not easy to get samples or conduct experiments. Like black band disease, brown jelly has a rather distinctive appearance and is composed of a diverse assemblage of microbes. What is still unclear is whether any of the microbial community causes tissue death, or if the tissue is already dying and the jelly is consuming dead tissue. The jelly can act as a contagious agent, and corals that contact the jelly may subsequently die with the presence of increasing amounts of brown jelly. This material could, however, simply be smothering the coral tissue, while consisting of a group of self-sustaining and rapidly multiplying constituents that do not actually constitute an "infection."

As I have mentioned before, the ciliates that have been presumed to "cause" brown jelly do not appear to cause it at all. They are consuming zooxanthellae and other material released from dying and decomposing coral tissue - performing a janitorial role of sorts. In analyzing the material, it is complex in its composition, including many microbes which I am wholly incapable of identifying. I asked a coral disease colleague of mine, Debbie Santavy, if she knew anyone who is a good protozoologist. As it turned out, her husband Richard Snyder, happened to be one. I left some brown jelly with him, and recently received his preliminary analysis.

He found the flocculent material to be dominated by algal cells, most of which were Symbiodinium (zooxanthellae). There was a fungal component that provided some structure to the material. He found several sizes and shapes of fecal pellets that contributed to the brown color also provided by the golden brown zooxanthellae and suspected they originated from copepods. I had noticed many Spirochaetes in the mix, which he identified as Spirulina. He also found flagellates, which were likely the very small fast-moving bugs I saw associated with the dying tissue. He suspected there would be a lot of amoebae present in the sample given the habitat, but they were not identified in the mix because they are easily lost in the fixation process. In contrast to my inexperienced eye noticing a couple types of ciliates, he was able to identify five or six different species, although none could be positively identified to a specific species. One of these ciliates was the species feeding on the zooxanthellae. There were also abundant bacteriovores feeding on the even more abundant heterotrophic bacteria, composed mostly of filaments and rods.

He suspected the microbial activity in the production and binding of polysaccharides was responsible for the material's gel-like flocculent consistency. In closing, he noted that he did not notice anything, except perhaps the fungi, that would cause harm to the corals. To quote, "I would consider this consortium to be your friend, flocculating the extraneous cast-off organisms and organic material so that you can keep it siphoned out of your tanks." That would be true were this material not able to cause further coral mortality as it grows and is blown around the tank by water currents. It is clear that there needs to be a lot of work done in isolating and culturing each of the consortium members to determine if any one of them actually causes tissue death in corals. In fact, it would require a considerable amount of time, effort, and money. I plan to injure some corals and keep them in rather stagnant tank water to see if I can induce a "brown jelly infection" and send Richard some live material. If I can find a way to reliably and consistently produce or culture brown jelly, it would make some sense to continue this work. With available material, I could try to infect corals by selectively treating the jelly with drugs that could eliminate some groups of the consortium and determine their individual effects. Otherwise, it appears that brown jelly will remain a mystery for the time being.

This Hydnophora sp. is affected with brown jelly, a condition well known to aquarists. The cause
of coral mortality by this material remains unknown.

An Unrelated Story That May Be Of Some Interest…

While not involving microscopic organisms, I have one final anecdotal report to provide to readers of this column. For nine years, I have had a soft coral in my tanks that has been spread extensively around the country. I originally acquired it from Scientific Corals, in Atlanta, as Litophyton arboreum. I am not convinced it was identified correctly, and it appears to me from examining its sclerites and gross colony and polyp morphology to be a species of Capnella. In any event, I have this colony spread throughout five tanks in my home and lab. It is a prolific producer of daughter colonies by branchlet dropping. It is also worth noting that both Capnella and Litophyton have very high densities of zooxanthellae, and are considered quite close to autotrophic corals, at least in terms of carbon produced by photosynthesis. Thus, one would expect their growth to be strongly correlated with irradiance levels.

Over the past three months, I have provided 46 daughter colonies to a local coral farm. What made me think about this was that almost all of the colonies were being produced from parent colonies in my large home system. I began thinking about the different tanks, and the relative contributions of light and food to growth and reproduction. While the tanks are, of course, very different they all have rock and sand that has been intermixed between them many times. These tanks all have seawater made from the same salts, and I use the same regimen of additions and maintenance on all of them, including food, calcium and alkalinity and nothing else. Water changes have not occurred at all during the period in question. The water quality parameters I measure are nearly identical and their values certainly fall within the variation found on natural reefs. Thus, I would consider them to be different, but not so different as to be somewhat like the differences between various reefs where a species is known to exist.

The tanks are described in the table below, and the time period is approximately three months to date.

Tank size
Colony sizes
Colony growth
# Daughters
Tank 1
2 x 65W power compact (one blue, one white)
Adult - 10cm max
Tank 2
18W fluorescent white actinic
Sub-adult, 3 cm
Tank 3
2 x 65W power compact (one blue, one white)
Tunze - estimated low efficiency
Sub-adult, 5 cm
Tank 4
2 x 400W 6500K
My Reef Creations, Beckett design, estimated high efficiency
Adult, 10cm max
Tank 5
2 x 175W 10,000K
Sub-adult, 5 cm
Slow to moderate

The variations in the number of daughter colonies produced, and the growth of colonies in the tank, is remarkably different under the different conditions. While many other variables might be involved, such as water motion, competition, and differences in food source amounts and types produced in situ from the various tanks, it is most likely that growth and reproduction are most directly attributable to energy availability. The difference in placement of the corals with respect to depth and subsequent light attenuation is assumed to be minimal since multiple colonies in each tank are found within similar ranges in all tanks.

So, one might assume that Tank 2 is simply too low in irradiance, and that the skimmer in Tank 3 is removing food sources that are present in tank 1, despite identical irradiance. Tank 1 produces daughters and adult colonies, while Tank 3 produces neither. In Tank 4, the very high light level might be responsible for the daughter colonies and rapid growth, but Tank 5 is an anomaly. It has higher irradiance than Tank 1; neither tank provides export of any kind, yet Tank 5 produces no daughter colonies or adult colonies.

Of course, none of this really means much. This is simply an anecdotal tidbit that I found interesting, and I offer it because it should at the very least spark some more debate in the Coral Forum with regard to light versus food in coral growth. It has become the aquarist's equivalent of heredity versus environment, and sometimes having so many tanks running with the same clonal lines gives me an opportunity to throw things like this out to the masses, if only for fun and lively discussion.

If you have any questions about this article, please visit my author forum on Reef Central.

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It's a Small World, After All by Eric Borneman -