What should we call those aquariums at home filled with corals, fish and piles of rocks? Coral gardens. Coral reefs. Natural systems?
‘The coral reef” an owner built, high density, fully serviced, self-sufficient housing estate in the desert- or is it?’ Kinsey 1991
The natural coral reef is composed of many zones, habitats, and types of reefs. A simple review of reef ecology will show us that coral reefs are found between 25 degrees North and 25 degrees South latitude. Established reefs are not usually established at temperatures much below 23 to 25 degrees C. A coral reef is an assemblage of skeletons of sedentary organisms that live in warm marine waters with strong illumination. Keeping these basic factors for coral reefs in mind, we will begin our investigation into captive requirements of corals.
Natural reefs are classified as to their type of structure and development. Of the types of reef structures, we have major and minor reef types. The major types are fringing, barrier, and atolls. The fringing reefs are reefs that form close to shore still upon the continental shelf. These are commonly associated with islands and large coastal shores. These reefs get a substantial force of wave action on the outer edge. The formation of the reef itself and the species of corals help dissipate this form to nearly a trickle at the near shore regions.
Barrier reefs are located farther from the coastline than fringing reefs. Between the barrier reef and the shoreline is a lagoonal area with reduced water flow that is buffered by the reef itself. A barrier is usually situated on a small ridge, or eroded island farther from shore.
The coral atoll is unique in that its not associated with a mainland, but with an island only. These structures are ring shaped formations that surround a lagoon that can be rather larger. Because these typically are formed in deeper waters or in the middle of the sea, these organisms tend to like higher water flow and food levels.
Other associated habitats to coral reefs include seagrass flats and mangrove forests. These provide a food source and safe nursery ground for the many associated fish species of the reef.
In a natural reef, there are always leading edge corals that are subjected to the full force of storms, waves, and the pounding surf. These are very close to the surface of the water as well. These corals are the reef crest corals, and are comprised mainly of fast growing branching or plate like species. These corals absorb and dissipate huge forces associated with the wave action of the ocean. These fast growing corals need to be prolific as they are frequently broken apart by storms and wave action and need to be able to replenish there formations in a short period of time. Because these corals are constantly bombarded by wave forces, they tend to build stronger skeletons and be denser than lower water flow corals.
We also have lagoonal corals, or those that are on the shoreward side of the reef. Since this can be such a huge region, there are many micro-zones with in this zone. Corals in these regions tend to require less water flow. In fact, many of them will do poorly if subjected to the crashing and violent forces of waves. The zone also may receive either less light or in some cases more light. Making it important to know what region your specimen came from.
What about coral reef ecology? Its important to focus on the ecology of the reef as well before we can fully understand how to care for these organisms in captivity. Ecology is the study of the interactions between organisms and their environment, while environment will be defined as all things extrinsic to the organisms that impinge upon it, including light, temperature, topography, parasites, predators, food, mates and competitors. As can be seen, as aquarists WE are solely responsible for the environment of the reef animals we keep. As aquarists, we should be concerned with meeting the optimal environmental conditions of our species. To simulate a proper environment we should look at biodiversity of the system. Biodiversity is the total number of organisms that inhabit a specific habitat. In our case, that habitat is a closed glass or acrylic box containing our corals and other animals. Obviously due to the nature of closed systems we will never come close to matching the biodiversity of the natural reef, but we can all do much better at matching it. Because we are creating ecosystems that comprise the environment of our organisms, we need to be concerned with population dynamics, energy (food, nutrient) dynamics, and community stability dynamics. All of these factors play a huge role in the captive eco-system. The rule of the reef is ‘specialize of die’. These animals have had millions of years to adapt to the often-harsh environmental conditions of the sea. Modern reefs have been around for about 220,000 years and have allowed for a lot of specialization. Each animal may have developed the ability to take advantage of a specialized niche environment. Possibly grazing a species of algae, or growing in a low water flow region, it all depends on the species.
Population dynamics on the reef aquarium is an often-overlooked subject of interest. Since we are essentially running closed systems, we have limited food availability. Although we may add some prepared foods to the system, we come no where close to the actual biomass of live and available foods found on a reef. We also have water quality issues. As good as, we can keep the water quality; any closed system with limited export will always fall behind the vastness of the ocean in water purity. With our limited biodiversity, we have limited symbiosis and commensal relationships. We as aquarists tend not to look at this when selecting species and often forget the roles these relationships play in nature.
We also forget about the role of energy dynamics. We all learned early on about food chains, and later about food webs. Even out closed reef systems need a population of producers, consumers, and decomposers. In a natural reef, one habitats is dependent on an adjacent habitat for certain cycling and export functions. An example of this would be the reef and the seagrass flats. So, in a reef aquarium we often focus solely on the nitrogen cycle. We constantly underfeed the animals, ignore the carbon cycle, and we combine communities and habitats haphazardly. Is it any wonder things don’t go smoothly? More importantly- this is a great testament to the durability of many of these species that can survive under these less than ideal conditions.
So, what can we do? Quit? Well, we are not really doing all that badly, although this may be more a testament to the survivability of the organisms than our ability as aquarists. Some starting points to solve this problem are to specialize like the reef. Lets face it, a closed box measuring 4 feet by 2 feet by two feet is NOT the Great Barrier Reef of Australia, so why then do we insist on packing it full of coral species? We should look at specializing for a particular zone or habitat to allow the best environmental conditions to exist for these organisms. This includes planning. Plan before buying; know where it comes from, and what the basic needs of these organisms are. Think about what is happening and why. Often people loose corals to competition among species in their tanks. These animals are only reacting the only way they know how- by defending against unknown predators or organisms that are encroaching on their survivability. Therefore, we should make every effort not to place incompatible species in close proximity. We should all ask ourselves why do we keep coral reefs. Is it to appreciate the beauty and splendor of the ocean? Is it to study the interactions of hundreds of species? Is it to have a colorful living room centerpiece? Alternatively, a chance to have what few others can keep. If we are just looking for beauty, then an interior decorator might make more sense for you than a reef aquarium. If you are the type of aquarist who is more impressed with owning rare and unusual species and having more, bigger, or better specimens then the hobby is also not for you. We need less ego/testosterone hobbyists and more hobbyists concerned with the general welfare and well being of the organisms they keep.
As aquarists, our essential job is good husbandry to maintain the proper environment. So we should keep animals that would exist in a single zone, this is easily done through research. If you have Internet access, there are many sites available to help you do this. A great site is the America Online Fish and Marinelife Forum or Compuserve’s FISHNET online forum. Even your very own club and other clubs like yours have very good informatio.  Then there are books. Many great books exist to help you better understand the role of ecology in the reef aquarium. There are some very good books by authors like Tullock, Michael, Fenner, and Borneman on these subjects.
I hope you have come away with a better appreciation of the approach needed to make your reef the best it can be. Some of the simplest things we can do NOW are to add biodiversity. By providing the proper habitat for the organisms, we can add many new species.