Corals are a group of exclusively marine, polyped animals in the phylum Cnidaria. As one can see from their basic body form, they are distant relatives of jellyfish. They can take the form of either individual polyps or colonies of perhaps hundreds or thousands of individual polyps.
They are divided into two basic groups, namely the hard corals and soft corals. Some may be surprised to find that these two groups aren’t very closely related; in truth, stony corals are more related to “normal” anemones whereas soft corals are more related to tube anemones (i.e. cerianthids).
They occur in many ocean habitats from deep waters, temperate waters or shallow tropical waters. However, it is the latter type that most aquarists are familiar with. It is in tropical reefs that stony corals predominate. These produce a hard, stone-like skeleton made of crystalline calcium carbonate called aragonite. They are the so-called reef-building types and are primarily responsible for the formation of the reef itself (the crusts, shells or tubes of certain algae, mollusks, worms, etc., which are also made of calcium carbonate, make some smaller contribution). Chunks of these deposits are known (especially by aquarists) as live rock.
Soft corals, including the gorgonians and sea fans, produce no such calcium hard skeleton. They may, however, produce a leathery (e.g. leather corals) or horny (e.g. gorgonians/sea fans) “skeleton.”
Most reef-building corals and many tropical soft species have a mutually beneficial relationship with special unicellular algae (called zooxanthellae). These algae live within the host’s gastrodermis. Up to 90% of the carbon fixed by the algae via photosynthesis is taken up by the coral. Similarly, certain bacteria known as diazotrophs supply a source of fixed nitrogen to the animal and its algal symbiont, and in return feeds on their organic waste products. Increasingly, the coral animal and its many, diverse microscopic partners are viewed as a single super-organism referred to as the coral “holobiont.”
In addition to these symbiotic relationships, many prey on zooplankton or even tiny fish (depending upon species and size). The coral uses its tentacles, armed with stinging cells (i.e. nematocysts) to stun, hold and kill its prey as it moves the item into its mouth. Following digestion, the waste is excreted from the same opening.
Success with these fascinating and beautiful creatures in captivity requires regular feedings of each species’ preferred food source(s) as well as intense illumination to promote photosynthesis of the zooxanthellae.
In this section you will learn which corals prefer which types of light and foods, as well as how to create the environment (e.g. water conditions) that they need to survive and grow.
Reef aquarium keeping has gotten a lot more sophisticated over the years. Fortunately, that doesn’t necessarily mean that it has gotten more complicated or more time-consuming. To the contrary, we now have the knowledge to create convincingly realistic representations of coral reef habitats with surprisingly minimal effort. While it’s true that we’ve now got some …
What’s the Difference Between PNS ProBio and PNS YelloSno? Read More »
Whether you are a dedicated, full-time coral farmer or a moderately invested hobbyist, reef aquarium keeping is risky business. This is due partly because of the inherent delicateness of corals in general, but also because coraliculture is still a relatively young (sometimes downright experimental) undertaking. Coral disease–and disease control–remains as one of the most poorly …
It should go without saying that the hermatypic, stony, reef-building corals will dominate most reef aquaria. Thankfully, so long as (1) key water parameters are monitored, (2) the appropriate light conditions are provided and (3) nutritious planktonic foods are present, these beautiful plant-animal symbiotic combos easily flourish even in the care of novice hobbyists. Especially …
Most people who are familiar with corals–whether admiring them in the wild or displaying them in a glass box–understand quite well that they are incredibly complex animals. This certainly is so with the zooxanthellate corals. Virtually all corals (zooxanthellate corals included) are predators of plankton and other tiny organisms, used as coral food. But the …
Enhancing Coral Nutrition with Purple Non-Sulfur Bacteria Read More »
There comes a time in this hobby when many aquarists grow bored of their beginner corals and they become interested in small and large polyp stony corals (SPS and LPS, respectively). For those of you who have been maintaining a “softie” reef (which includes coral such as zoanthids, mushrooms, leathers, and star polyps), you may …
Reef aquarium keepers are always looking for that one oddball “piece” of coral that will really make their aquarium display shine. Sometimes this is just something a little different in terms of ecology or behavior. Other times it is something that is atypical in terms of shape or placement. Quite often it is something that …
Advancements in the reef aquarium hobby have been developing at a dizzying pace. As our understanding of coral reef biota (and how to care for them in captivity) grows, many more tools are becoming available to those who wish to keep increasingly specialized aquarium systems. As of late, there has been a particularly strong interest …
Carnation Corals in the Home Aquarium: A New Hope of Success? Read More »
Aquariums: The New Medicine You enter the waiting room of your doctor’s office and you know she’s not going to be happy about your blood pressure and weight gain. Your palms start to sweat as you try to think of excuses for your bad habits and lack of exercise. As your pulse quickens, you look …
When thinking about crustaceans many creatures come to mind like shrimp or lobster. And while your mind may be wandering toward an all you can eat buffet, there is another type of crustacean that isn’t so tasty to humans, but boy do the fish love them. I speak of the mighty (and tiny) copepod. Copepod …
What are Sustainable Aquariums? An aquarium is a cornerstone of many homes and apartments, but how often have you come home to find your fish floating belly up? Whether the kids forgot to feed them or neglected to change the water filter, the bottom line is it’s time to go out and get a few …
