AHABS... Issue One

The Need For “Periodicity” In Reef Aquaria


Ronald L. Shimek, Ph. D.

An Obsession Amongst Hobbyists

I am sure every aquarist who reads these words will remember having heard the advice, “Whatever you do, make sure that the temperature (or salinity, or pH or… any factor you want to mention) in your aquarium does not vary much.” In essence, one of the first things every marine aquarist is given is the advice that that the system in all its glorious complexity should be kept as invariate as possible. This is often referred to as keeping the system “stable.” It seems like logical advice, particularly when many of the aquarium references refer to scientific documentation that “reefs are stable.” Reefs are stable, and that means aquaria should be stable, if they are going to emulate reefs. End of statement, no discussion necessary!

Well, maybe, and maybe not.

There are a couple of problems with the dogmatic statement underlined above which are probably not apparent to the casual reader, and I would like to take the time to make them explicitly apparent.

The Problems

The first, and very real, problem is the perception held by most hobbyists that coral reefs have been scientifically studied for a long time and that there is a great body of knowledge about them. I find it necessary to put some real limits on such perceptions. The term “long time” and “great body of knowledge” are both terms that are truly wrapped in the cloak of ambiguity. In this particular context, they lack explicit definitions and, consequently, mean different things to different readers. While reefs have certainly attracted attention of naturalists and learned people since the time of Aristotle, the beginnings of modern coral reef ecology are a lot closer to us than is the tutor of Alexander the Great.

In spite of a few descriptive works about coral reefs (see, for example, Wells, 1957) and a correspondingly sparse set of intensive studies about specific animals or animals groups (see, for example, Kohn, 1956, 1958, 1959), detailed and rigorous ecological studies on coral reefs really did not start until the early 1950s with the publication of the Odums' 1955 landmark monograph on Eniwetok Atoll. Although much subsequent ecological work was done on coral reefs in the...

The Cnidaria, The Reason For The Hobby


Ronald L. Shimek, Ph. D.

Who Are Cnidarians?

There is good reason to spend a bit of time learning the basics about the group animal that biologists lump together as under the blanket term: Cnidaria (Pronounced: Nigh-dare- ee -ya). That reason goes hand-in-hand with the reason to consider this group of animals as THE reason for all of the coral reef or marine fish keeping hobby. Without the animals that constitute the Cnidaria, there would be no coral reefs, or coral reef fish. So, what is “The Cnidaria?” Well, simply put, this is the major taxonomic animal group, or “phylum,” which contains corals and all the animals that are closely related to them.

This group is a diverse one! It consists of more than 10,000 species of corals, sea anemones, soft corals, hydroids, and jellyfishes. All of these animals, though, share a lot of similar characteristics. I think it is useful for aquarists to know these shared or common characteristics; knowing the characteristics shared by all members of a group can provide someone with sufficient information that I can make some educated guesses as to the care of a particular specimen. In this case, knowing the phylum characteristics, or the characteristics of the particular subdivision of that phylum called a class, may make the difference between success and failure in the care of an unknown coral or sea anemone.


  • Class Hydrozoa - Hydroids, Portuguese Man O' War, Fire Corals.
  • Class Scyphozoa - Jellyfish
  • Class Cubozoa - Box Jellyfish; Sea Wasps.
  • Class Anthozoa - Sea Anemones, Corals, Soft Corals, Sea Pens, Sea Whips.

Taxonomy is the subdivision of biology concerned with the “grouping” of organisms. Often characterized by ignorant people as “pigeonholing,” taxonomy attempts to show the effects of evolution by grouping together all those animals descendent from a common ancestor. This principle of common descent holds at each level of the taxonomic hierarchy. In this case, then, all cnidarians share a common ancestor, then within that huge group of related organisms, all hydrozoans, scyphozoans, cubozoans, and anthozoans each have a common ancestor. However, those common ancestors all shared some characteristics as all of them were, first and foremost, cnidarians....

Copepods in the Reef Aquarium


By Ronald L. Shimek, Ph. D

Point Of View

The infinite arrogance of many humans is reflected in their tendency to think of themselves as “the masters of creation;” the most important beings on the planet. There is indeed evidence that Homo sapiens , a misnomer if ever there was, in aggregrate may well be capable of destroying much of the world's life. The final outcome of mankind's war on the biosphere will not be known for some time; even so, a reasonable argument may be made for considering man as a transitory blip on the radar screen of Earth's life forms, and that the real movers and shakers of the world are much smaller in individual stature. Bacteria have ruled the world for billions of years, and are still the dominant life forms, and even amongst those creatures that may be termed animals, the influence of man is likely over stated, due to our anthropomorphic viewpoint. There are a couple of animal groups, each of which containing individuals wearing their skeletons on the outside, that could certainly dispute the assumption of human importance. One of these groups, the nematodes, or roundworms, is largely ignored by aquarists. Most of the smaller animals in the other group, the arthropods, are lumped together by aquarists and dismissed with the demeaning sobriquet of “pods;” it isn't even worth the trouble to learn to distinguish a few of the more common types sufficiently to make the effort of learning their names.

Arthropods Rule

On land, the dominant forms of animal life, in terms of the number of species and in terms of mass of the animals, are certainly the insects. Literally millions of different kinds exist, and the sheer amount of insect flesh is almost incalculable. Arthropods dominate the oceanic realm as well; interestingly enough though, there the dominant crustaceans are not insects. For some obscure evolutionary reason, insects are almost totally absent from the seas. There about 30 species of wholly oceanic sea skaters, all in the genus Halobates , and numerous insects living in intertidal habitats, but no insect truly lives a submerged marine existence. This is really rather odd, as insects dominate underwater habitats in fresh water much as they do on the land.

Here is a link to images of Halobates , with information on the life history and reproduction, while here is a link to information about the evolution of that group.

For whatever reason, the majority of the arthropod component of oceanic life is largely crustacean, although representatives of the chelicerates (a different arthropod group, containing spiders, mites and their kin) represented by horseshoe crabs, pycnogonids , and mites, are not uncommon. Insects, crustaceans, and chelicerates all shared a common ancestor, probably a trilobite or similar animal, about 500,000,000 years ago; however, they have diverged significantly since that time. Each of these groups is distinct. Clearly...

Ron Shimek