In previous coral reef post, I stressed the need for superb water quality. Some of you may have wondered why many tropical areas are oligotrophic (nutrient-poor) by nature. Since temperate parts of the world seem to be heavily inundated with an abundance of nutrients. One of the main reasons is due to the fact that nutrient-rich water. After a long journey through the deep sea, is constantly imported by offshore currents along the coasts of many temperate areas. Most of the world’s temperate coastlines are directly affected by up welling currents. And this is one of the reasons that kelp/macroalgae habitats are common in these areas.
Tropical coral reefs export rather than import nutrients through strong wave action and currents. Furthermore, the biological interactions which exist on coral reefs are so tightly interwoven that most nutrients freed through biological processes are simply sucked right back up into the system and recycled. Just like the real estate on a calcareous reef, nutrients are hard to come by and are plucked up as if they were hotcakes. Besides having crystal-clear water, tropical reefs are also remarkably “sunny” places. Unlike Northern England or Seattle, Washington, the tropics receive near constant bombardment by the sun’s intense U.V. rays.
The tropics experience fewer cloudy or overcast days per year than do other latitudes. And they also receive a greater amount of sunlight. The angle of incidence effects light’s ability to penetrate the atmosphere and ocean surface. If you hold a flashlight at an angle and stare into the bulb, your eyes would probably be just fine. But if you look straight into a flashlight head on, you might be temporarily blinded. This is a good example of light’s angle of incidence and how it affects intensity.
Since corals depend so heavily on light in order to survive. And we know that light rays are amazingly strong at the equator. It makes sense that we must strive to create a very bright environment in case keeping coral for saltwater tank. The term brightness, however, means very little to the experienced reef aquarist. Light, just like sound, varies in wavelength, as well as intensity. Certainly, there is a huge difference between one of Beethoven’s symphonies and the sharp sting of an air horn. Imagine that corals, in the same way that people can tolerate certain frequencies of sound, enjoy certain wavelengths of light and dislike others. Since water serves as a very good filter for most of the visible light in the spectrum, corals have, over time, evolved and adapted to specific “colors” of light. These wavelengths happen to be those which penetrate water the most effectively.
When you are underwater, everything seems to look blue, green and grey. Notice how reds and yellows become drab the deeper you go. Since blues and greens, or wavelengths near 400-450 nanometers penetrate the ocean so well, corals absolutely depend on this band of energy to survive. This is of great importance to the reef aquarist, since many of the bulbs offered for sale at pet stores produce high intensity red and yellow light, and little blue light. The reason manufacturers produce these bulbs is simple. Corals, fish, and decorations look their best under red/yellow light since this wavelength seems to bring out their vibrant colors best.
When purchasing lights for a reef tank, however, it is wise to pick bulbs which most closely match the wavelengths which are found in the natural environment. Do not buy bulbs which only make your critters look vibrant. Sure, you may get a few oohs and ahhs, but they will be temporary gasps of amazement since your tank’s inhabitants will soon be dead. Luckily, the recent boom in the reef keeping hobby has brought about an awareness of this issue, and it’s quite easy to find the perfect lighting system.
I would like to mention one other matter before I end this article. Now that we have covered the basics of light and water quality, some people might wonder what other aspects of the aquatic environment remain to be discussed. One issue that frequently gets left out of many popular texts is the bioload factor. For those familiar with fish-only aquariums, there is an old rule of thumb which states “one inch of fish per gallon of water”. How does this rule apply to reef tanks?
First of all, there are very, very few “rules” in the reef keeping hobby at all, and anyone who tells you otherwise should be looked at with great skepticism.
Even in regards to fish-only tanks, this rule of thumb is silly. Why? Different species of fish produce varying amounts of biological waste.For example, a six inch triggerfish which feeds on raw meat and goldfish will certainly present a greater stress on a filtration system than would a six-inch pipefish. Some people recommend calculating actual body mass as a way to decide how many fish an aquarium can handle. This, in my opinion, is just as silly. A large angel fish with the same body mass as a triggerfish just doesn’t produce the same amount of waste. Triggers are messy fish, whereas angels tend to be delicate, nit-picky eaters. Furthermore, a tank with a wet/dry filter, protein skimmer, mechanical canister filter, U.V. sterilizer, and ozonizer will certainly be able to process a heavier bioload that one which only benefits from a single wet/dry filter.
Once again, the old trustee “rule of thumb” falls apart. Corals, like fish, come in all sorts of shapes and sizes, and also vary in their capacity to produce waste. If you’ve ever seen a picture of a coral reef, or had the privilege of diving one, you undoubtedly noticed that most sections of living reefs do not look like the pictures of beautiful aquariums you see in magazines and books. For the most part, corals simply cannot coexist in such tight orderly fashion with one another. Remember, it’s a dog eat dog competition for space and resources out there. This is not to say that a tank jam-packed with corals is an unhealthy tank. Tt is merely a word of caution. I once read an article which stated that the average two-inch damsel fish. Nn nature, has the equivalent of 2,000 gallons of water in which to live.
Perfect Setup is a Must
It would be mighty depressing if we were forced to purchase huge. Ten foot long tanks in order to keep a lone damsel. The point is that many ocean creatures are accustomed to a large amount of space to move about in and live. Corals, though sedentary, need space too. Many species of corals have evolved specialized defense mechanisms to ward off would-be intruders. These include stinging, nematocyst-lined sweeper tentacles and various methods of chemical warfare. Since we should attempt to duplicate nature in the home aquarium, it is appropriate to keep these factors in mind. Beware of placing coral reef too close together.
Some specimens, such as certain species of soft corals that produce harmful biotoxins, should also be watched closely. As long are your aquarium’s inhabitants live peacefully and appear healthy. Then there really is no limit to the number of animals you may stock your tank with. Do not, however, purchase a thoughtless assortment of animals, place them in your tank haphazardly, and hope for the best. This would be cruel and pointless, since your animals would undoubtedly harm themselves, and might even die.
Next Part will be part three of this series on Coral for Saltwater Tank.
By Jason Kim
Jason is the founder of AquaC. Inc.