Zonation Aquarium.Net Dec 96
By Dana Riddle
My first experience with an aquarium was the same as countless others. A Christmas gift for my brother, the 15 gallon Metaframe tank (with stainless steel frame and slate bottom) was quickly filled with water. Fishes soon followed - a couple of neon tetras, a black molly and freshwater angelfishes and "sharks". I inherited the tank when my brother lost interest. I read quite a few aquarium books and learned that, although we had achieved a degree of success with the tank, we had really bent one of nature's rules - the rule of zonation.
Zonation is defined as "distribution of organisms in a biogeographic zone". The Amazon River could be characterized as an acidic, soft water biogeographical zone while Africa's Lake Malawi is a alkaline, hard water zone. Does that mean that neon tetras and African cichlids can't be kept in the same aquarium? Of course not, but compromised community tanks such as this may never be truly successful.
There are marine environment biogeographic zones just as there are in freshwater environments. In coral reef zonation, the issues tend to be less of water chemistry than of light and water motion. Can we mix animals from different reef zones? Of course. The "average" reef tank seems to house a large soft coral or anemone in the center of the tank and is surrounded by stony corals that sometimes seem to be an afterthought. These tanks can be incredibly beautiful. But are they truly successful? Are all animals growing at rates equal or greater than in nature? Do some corals thrive while others do not? As an example, the aquarist may be emboldened by success with a, say, Plerogyra (Bubble coral) may purchase a Staghorn coral ( Acropora sp.) with tiny, purple-tipped branches. When the Acropora dies a month later, the hobbyist brands it as difficult to keep. In reality, the Acropora is probably as easy to keep as the Bubble coral. The hobbyist simply bent, and broke, the law of zonation. (In a case such as this, the Acropora specimen probably perished as a result of poor water movement and/or insufficient lighting. Or it may have been a victim of the Plerogyra 's aggressive interaction. Conversely, the Bubble coral would probably not do very well in an aquarium designed to meet the Acropora' s needs.)
There are many types of corals reefs - fore reefs, back reefs, lagoonal reefs. (There is a general description of these in my book "The Captive Reef".) Each reef zone has its own peculiarities. We would do well to research the areas from which a coral is found and then mimic the light and flow patterns of that zone. Some reefs share enough similarities so we can mix and match corals of different zones. For instance, we'll probably be OK in mixing animals from a lagoon with those from a sheltered back reef. Generally, these areas include corals such as Hammer, Anchor, Frogspawn, Octopus (all Euphyllia species), Bubble ( Plerogyra ), Elegance ( Catalaphyllia ) and Meat ( Cynarina ) specimens. Small polyped stony corals such as many Staghorn ( Acropora ), Bird's Nest ( Seriatopora ) and others typically will not do as well in these aquariums. We don't give a second thought to a freshwater hobbyist setting up an Amazon tank, a Lake Malawi tank, etc. In fact, it probably raises eye brows to see a mixture of these fishes in a single tank. Should we expect any less in a reef aquarium? Have we decided that mixing animals from different reef zones is OK? Should we accept the losses that are sure to come as a result of flow and light incompatibility or those that result from the chemical warfare between soft and stony corals?
Lest you think I'm preaching and won't get off the soap box, let me give an example. I have been very fortunate to travel from coast to coast and view many reef aquariums. I almost always carry my "light" meters - those that measure photosynthetically active radiation (PAR) and ultraviolet radiation. Happily, I have never been turned down when I request to make radiation readings within the aquarium. After more than a few measurements, I began to see trends emerging. Today, I love to see aquariums with a fat, happy Plerogyra (Bubble coral) specimens. I brazenly predict what sort of light reading I'll get before actually making the measurement. (I'm sometimes a little off - in a recent trip to Portland, OR, I predicted a reading of 175 µE. The measurement was actually 176, with the probe being held in a steady, vertical position.) In my experience, Bubble corals thrive when the PAR reading is 150 - 180 µEinsteins and current is strong enough to bathe all "bubbles" in flow without distortion. Staghorn corals tend to do only fairly well in these tanks (probably as a result of poor water movement). Similarly, those tanks with really colorful Acropora specimens have very good water movement and PAR readings of 350 µE and better, sometimes much better. These tanks tend to have relatively high amounts of UVA radiation as well.
We are only just beginning to understand the requirements of different corals. The best advice to the hobbyist is to continue to learn as much as possible about the animals we are keeping. Read as much as possible those books and articles published in the last 2 years or so - it is there that some mysteries of the captive reef are being explained.
Last modified 2006-11-23 01:37